Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Directional Well Planning and Trajectory Design Calculations - “Review”
Zahoro Athumani, Department of Petroleum Engineering
China University of Geosciences (Wuhan) January 15, 2018 Class Report
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
ABSRACT Directionally drilled wells represent an efficient way to reach special targets that are difficult to reach using vertically drilled wells. The objective of steering a well trajectory in the
right direction and hitting a geological target many kilometers downhole has forced the drilling industry to really focus on tools and methods to identify wellbore location and its path during drilling. In the early days of drilling exploration, it was common to set the drilling rig right above the target and drill a vertical well into it. Later, it became necessary to drill wells to reach targets that were deviated from the reference location at the surface. Throughout the years, many tools and methods have been developed for directional drilling. There are several companies offering tools to deflect and steer wellbores in the right direction and to measure wellbore inclination and azimuth. The directional survey measurements are given in terms of inclination, azimuth and 3D coordinates, TVD, northing and easting at the depth of the survey station. For many applications, the accurate position and direction of the borehole should be determined at depths which may not coincide with the depth of survey stations. The main purpose of this report is to show how a directional well path or trajectory such us the build-and-hold (Slant - Type), build-hold-and-drop (S - Type), and Continuous-build (J - Type) is planned and designed, and how parameters pertaining to these well trajectories are calculated after receiving some of the important data from the geologist and / or reservoir engineer. Also the application of trajectory design in a case study is presented. Key Words: Directional Drilling, Well Planning, Well Path / Trajectory, Kick-Off Point, Build Rate, End of Build, Total Vertical Depth.
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
CONTENTS ABSRACT ............................................................................................................................................. i 1.
2.
INTRODUCTION ......................................................................................................................... 1 1.1.
The Conception of Well Trajectory and Directional Drilling ........................................... 1
1.2.
Principles of Directional Drilling ..................................................................................... 2
1.3.
Directional Drilling Operations ........................................................................................ 5
1.4.
Background ...................................................................................................................... 6
PLANNING AND DESIGNING OF A DIRECTIONAL WELL ............................................................. 8 2.1.
Reasons for Drilling a Directional Well ......................................................................... 10
2.2.
Types of Directional Wellbore Profiles / Trajectories..................................................... 16
2.3.
How to Plan Directional Well Profile ............................................................................. 19
2.3.1.
Parameters defining the well path .......................................................................... 20
2.3.2.
Target and Geography of the Location ................................................................... 21
2.3.3.
Defining the well path ............................................................................................ 23
2.4.
3.
Illustrations Showing Calculations for the Well Paths (Trajectories) ............................. 23
2.4.1.
Build-and-hold (Slant) Well Trajectory.................................................................. 24
2.4.2.
Build-hold-and-drop (S-type) Well Trajectory ....................................................... 27
2.4.3.
Continuous-build (J) Well Trajectory ..................................................................... 30
PRACTICAL APPLICATION OF WELL TRAJECTORY DESIGNING THROUGH CASE STUDIES ........ 31 3.1.
Case Study 1 ................................................................................................................... 31
3.2. Case Study 2: “Well Asal 5: An example of a well profile in the Asal Rift Geothermal Field .................................................................................................................................................... 32 3.3. 4.
Advantages of the Build-and-hold (Slant) Well Trajectory ............................................ 37
CONCLUSION ........................................................................................................................... 38
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
LIST OF FIGURES Figure 1 Measurement parameters of a directional well (modified from Gabolde and Nguyen, 1991) ................................................................................................................................................. 1 Figure 2 Using the BHA to change angle (Kate, 2014)..................................................................... 4 Figure 3: 3-D Visualization of well paths / trajectory ....................................................................... 9 Figure 4 – 3D well profile (Gruenhagen, H et al., 2002) .................................................................. 9 Figure 5 Relief Well Directional Designing (Flores et al. 2014).................................................... 16 Figure 6 Most common types of directional wellbore profiles ...................................................... 17 Figure 7: Well planning reference systems ..................................................................................... 22 Figure 8 Illustration for Build-and-hold well trajectory calculation ............................................... 25 Figure 9 Illustration for Build-hold-and-drop well trajectory calculation....................................... 28 Figure 10 Illustration for Continuous-Build (J-Type) well trajectory calculation........................... 30 Figure 11 J Profile Directional well plan (Jones et al., 2008) ......................................................... 32 Figure 12 Temperature profile, geology, thermal alteration and TEM based resistivity model for well 5 (modified from Árnason and Flóvenz, 1995) ....................................................................... 33 Figure 13 Geometry of Asal 5 Well build-and-hold Trajectory (manual sketch) ............................ 35
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
1. INTRODUCTION 1.1.The Conception of Well Trajectory and Directional Drilling Xiang Wu and Kanjian Zhang, 2015, defined a well trajectory as a three-dimensional curve, where the trajectory is described as a combination of turn sections and straight sections. The main objective of designing a horizontal well trajectory is to construct a trajectory that reaches a given target at a specified inclination and azimuth from a given starting location subject to various constraints arising from engineering specifications. In the oil and gas industry, geometric boreholes (i.e. non-vertical, shaped boreholes) are produced by the process of directional drilling. This involves steering a drilling tool in a desired direction along a path defined by a team of reservoir engineers, drilling engineers, geosteerers and geologists (Martin et al., 2017). Directional drilling is described as the deflection of a wellbore in order to reach a pre-determined objective below the surface of the earth. Figure 1 below shows the main parameters of a directional well which will be defined in subsequent sections of this report.
Figure 1 Measurement parameters of a directional well (modified from Gabolde and Nguyen, 1991)
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Directionally drilled wells represent an efficient way to reach special targets that are difficult to reach using vertically drilled wells. While a drawback of directional drilling is higher cost as one of the most expensive operations involved in the exploration and development
of oil and gas reservoirs is typically the drilling of the wellbores, its advantage is that, surface construction may be minimized while still reaching the intended targets. The main factor in the cost of a directional well is the horizontal distance to the target. In the
prevailing market conditions of relatively high costs and low oil and gas prices, across much of the world most oil and gas companies are particularly keen to minimize their drilling costs (Khaled et al., 1999). Previous studies indicate that the cost of drilling a horizontal well is about 1.4 times the cost of drilling a vertical well (S. D. Joshi, 2003). The attraction of drilling horizontal and directional wells is that they can contact a greater volume of the reservoir and can transect the highest quality zones more effectively than vertical wells, resulting in higher production and recovery rates. In both cases one of the most important factors affecting the cost of drilling is length of the wellbore and the time taken to drill to the reservoir target. Thus any possibility to reduce the length of the wellbore, within the constraints of acceptable curvatures and geological obstacles, typically reduces the time it takes to reach the target and thereby reduces the total drilling costs. Optimizing wellbore lengths by designing a well trajectory, subject to a defined set of constraints, typically is desirable as a means of improving the economics of drilling operations. 1.2.Principles of Directional Drilling Most directional wells begin as vertical wellbores. At a designated depth, known as the kickoff point (KOP), the directional driller deflects the well path by increasing well inclination to begin the build section. Surveys taken during the drilling process indicate the direction of the bit and the tool face, or orientation of the measurement sensors in the well. The directional driller constantly monitors these measurements 2
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
and adjusts the trajectory of the wellbore as needed to intercept the next target along the well path. Initially, directional drilling involved a simple rotary bottomhole assembly (BHA) and the manipulation of parameters such as weight on bit (WOB), rotary speed and BHA geometry to achieve a desired trajectory. Changes in BHA stiffness, stabilizer placement and gauge, rotary speed, WOB, hole diameter, hole angle and formation characteristics all affect the directional capability and drilling efficiency of a BHA. By varying stabilizer placement in the drillstring, directional drillers can alter side forces acting on the bit and the BHA, causing it to increase, maintain or decrease inclination, commonly referred to as building, holding or dropping angle, respectively. Building the Angle: The directional driller uses a BHA with a full gauge near-bit stabilizer, another stabilizer between 15 to 27 m [50 to 90 ft] above the first and a third stabilizer about 9 m [30 ft] above the second. This BHA acts as a fulcrum, exerting a positive side force at the bit. Holding or Maintaining the Angle: The directional driller uses a BHA with 3 to 5 stabilizers, placed about 9 m apart. This packed BHA is designed to exert no net side force. Dropping the Angle: The directional driller uses BHA with the first stabilizer 9 to 27 m behind the bit. This BHA acts as a pendulum, exerting a negative side force at the bit. See figure 2 below.
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Figure 2 Using the BHA to change angle (Kate, 2014).
Bending of the pipe above a bit influences borehole deviation. Through strategic placement of drill collars and stabilizers, the directional driller can increase or decrease flexibility and bowing of the BHA to build or drop angle. During well planning, the directional driller must consider several factors to determine the required trajectory, particularly dogleg severity (DLS) as well as the capabilities of the BHA, drillstring, logging tools and casing to pass through the doglegs. The DLS refers to the rate of change in wellbore trajectory, measured in degrees per 30 m [100 ft]. It is also called build up rate. Drilling limitations include rig specifications such as maximum torque and pressure available from surface systems.
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Geologic features such as faults or formation changes need to be carefully considered; for example, very soft formations may limit build rates, and formation dip may cause a bit to walk, or drift laterally. Local knowledge of drilling behavior enables the directional driller to derive the correct lead angle needed to intercept the target. The skill of the directional driller lies in projecting ahead, estimating the spatial position of the bit and, based on the specific circ*mstances, deciding what course to take to intercept the target or targets. In the early days of directional drilling, a manual slide rule device was used to calculate the toolface angle required to drill from the last survey station to a target. Nowadays, computer programs perform the same function. 1.3.Directional Drilling Operations To steer a well to its target, directional drillers employ the following techniques: Jetting: A jetting assembly provides directional capability while drilling through loose or unconsolidated formations. Jetting bits are roller cone bits with either a large extended nozzle in place of one of the cones, or with one large nozzle and two small nozzles. The large nozzle provides the “high side” reference, and the well path is deflected by alternately sliding or rotating the drillstring. Nudging: This technique is often used in top hole sections, where several wellbores in close proximity to one another can pose magnetic interference issues and increase the risk of collision with other wellbores. The well path is nudged, or deflected, from vertical to pass the hazard then steered back to vertical when the hazard has been passed. Kicking-off: Diverting a well path from one trajectory to another is called “kickingoff”. The number of KOPs in a single well path depends on the complexity of the planned trajectory.
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Sidetracking: Deflecting a well path from an existing wellbore, or side-tracking, is performed for a variety of reasons such as avoiding a well collapse, a zone of instability or a section of previously drilled wellbore containing unretrieved fish (Junk or tools left in the well). This technique is also used to initiate multilateral drilling operations. Operators also drill vertical pilot holes to confirm reservoir true vertical depth (TVD), then side-track horizontally to maximize reservoir exposure. They sometimes sidetrack wells when expected targets are not encountered. Whipstock operations: A whipstock is a wedge-shaped steel tool deployed downhole to mechanically alter the well path. The whipstock is oriented to deflect the bit from the original borehole at a slight angle and in the direction of the desired azimuth for the sidetrack. It can be used in cased or open holes. Geosteering: Geosteering uses formation evaluation data obtained while drilling primarily through measurements-while-drilling (MWD) or logging-while-drilling (LWD) sensors to provide real-time input for steering decisions in horizontal and high-angle wells. Recent improvements in telemetry allow MWD and LWD data to be transmitted faster and with greater data density than in the past, greatly increasing the accuracy with which the well trajectory can be controlled. 1.4.Background The objective of steering a well trajectory in the right direction and hitting a geological target many kilometers downhole has forced the drilling industry to really focus on tools and methods to identify wellbore location and its path during drilling. In the early days of drilling exploration, it was common to set the drilling rig right above the target and drill a vertical well into it. Later, it became necessary to drill wells to reach targets that were deviated from the reference location at the surface. Throughout the years, many tools and methods have been developed for directional
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
drilling. There are several companies offering tools to deflect and steer wellbores in the right direction and to measure wellbore inclination and azimuth. The directional survey measurements are given in terms of inclination, azimuth and 3D coordinates, TVD, northing and easting at the depth of the survey station. For many applications, the accurate position and direction of the borehole should be determined at depths which may not coincide with the depth of survey stations. A mathematical tool for interpolating between survey stations is then required. Most wells drilled nowadays are horizontal wells, which consist of a vertical part, a curved part known as a build section, and a horizontal section which is steered with respect to geological features in order to maximize oil recovery from a reservoir (Williams, 2010; Shengzong et al., 1999; Li et al., 2009). Directional drilling can be achieved by either, Rotary Steerable Systems (RSS) (Baker, 2001; Tetsuo et al., 2002) and / or conventional slide directional drilling approaches (Baker, 2001; Kuwana et al., 1994) The main purpose of this report is to show how a directional well path or trajectory is planned and designed, and how parameters pertaining to the well trajectory are calculated after receiving some of the important data from the geologist and / or reservoir engineer. Also the application of trajectory design in a case study is presented.
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
2. PLANNING AND DESIGNING OF A DIRECTIONAL WELL The well planning process starts from geologists and reservoir engineers who decide the best place for the wellbore. They may only need to determine a single target, which will often be a tolerance of about 330 ft (100 m) around a certain target point. In this case, the angle at which the well enters the target can have various degree of deviation from the plan since a plan requires hitting only one target. On the other hand, it might be necessary for the well to penetrate multiple targets, with the final target being increasingly complex. This requires what is known as “Geosteering”, (The intentional directional control of a well based on the results of downhole geological logging measurements rather than three-dimensional targets in space, usually
to
keep
a
directional
wellbore
within
a
pay
zone
(http//:
glossary.oilfield.slb.com)). The drilling engineer therefore needs to examine potential surface locations (if more than one is available) and design a well path which meets all necessary target requirements at the lowest possible cost. Cost can be minimized most effectively when there is a certain degree of flexibility when it comes to the surface location. In the modern world, most directional-well planning is done on the computer. Modern computer technologies, such as 3D visualization and 3D earth models, have provided geoscientists and engineers with integrated and interactive tools to create, visualize, and optimize well paths through reservoir targets as illustrated by Figure 3 below. Furthermore, recently developed Geosteering systems and RSSs allow more-complex directional-well trajectories that are designed to drain more of the reservoir. The future is the real-time integration of the drilling and logging-while-drilling (LWD) data with Geosteering and the earth model. The 3D visualization of real-time data, together with the earth model, would allow integrated knowledge management and real-time decision making. 8
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Figure 3: 3-D Visualization of well paths / trajectory (http://petrowiki.org/File:Devol2_1102final_Page_271_Image_0002.png) The 3-D well design has changes in both inclination and azimuth. Another example of 3-D well profiles is illustrated in figure 4 below.
Figure 4 – 3D well profile (Gruenhagen, H et al., 2002) 9
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
When designing a directional well and hence a well trajectory / path, it is important first, to understand the reasons for drilling such a directional well, and second, to be familiar with the types of directional wells in the industry. 2.1.Reasons for Drilling a Directional Well Directional and horizontal drilling have been used along a predetermined trajectory to reach a subsurface targets beneath adjacent lands, reduce the footprint of gas field development, increase the length of the "pay zone" in a well, deliberately intersect fractures and construct relief wells. The target may be geometric and even adjusted in real time based on Logging While Drilling (LWD) and Measurement While Drilling (MWD) measurements. The following are some of the many reasons for drilling a non-vertical (deviated) well. Drilling Multiple Wells from a Single Location It is widely employed in the North Sea. The development of these fields is only economically feasible if it is possible to drill a large number of wells (up to 40 or 60) from one location (platform) without moving it. The deviated wells are designed to intercept a reservoir over a wide area. Many oil fields (both onshore and offshore) would not be economically feasible without directional drilling.
(Bourgoyne at al., 1991)
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Fault drilling. It is often difficult to drill a vertical well through a steeply inclined fault plane to reach an underlying hydrocarbon-bearing formation. Instead, the wellbore may be deflected perpendicular or parallel to the fault for better production. In unstable areas, a wellbore drilled through a fault zone could be at risk because of the possibility of slippage or movement along the fault. When a well is drilled across a fault, the casing may be damaged by fault slippage. Formation pressures along
(Bourgoyne at al., 1991)
fault planes may also affect hole conditions. Inaccessible locations A well is directionally drilled to reach a producing zone that is otherwise inaccessible with normal vertical-drilling practices due to some obstacles such as river estuary, mountain range, and city. The location of a producing formation dictates the remote rig location and directional-well profile. Applications like this are where “extendedreach” wells are most commonly drilled.
(Bourgoyne at al., 1991)
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Side-Tracking and Straightening It is, in fact, quite difficult to control the angle of inclination of any well (vertical or deviated) and it may be necessary to ‘correct’ the course of the well for many reasons. For example, it may be necessary in the event of the drillpipe becoming stuck in the hole to simply drill around the stuck pipe (or fish), or plug back the well to drill to an alternate target. Drilling around these obstructions, such as a lost string of pipe, is usually accomplished with a blind sidetrack. Oriented sidetrack is required if a certain direction is critical in locating an anticipated producing formation. Therefore, this technique may be employed either to drill around obstructions or to reposition the bottom of the wellbore for geological and engineering reasons.
Multiple sidetracking
Straightening
(Bourgoyne at al., 1991)
(Bourgoyne at al., 1991)
Sometimes multiple sidetracks are used to better understand geology or to place the wellbore in a more favorable portion of the reservoir. Straightening in sidetracking drilling is a special application of directional drilling implemented in order: to keep from crossing lease lines, to stay within the specifications of a drilling contract, and, to stay within the well spacing requirements of a developed field
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Salt-dome Drilling Producing formations can be found under the hard, overhanging cap of salt domes. Drilling a vertical well through a salt dome increases the possibility of drilling problems, such as severe washouts, moving salt, high pressure blocks of
dolomite, lost
circulation, and corrosion. Salt domes (also called diapirs) often form hydrocarbon traps in what were overlying reservoir rocks. In this form of trap, the reservoir is located directly beneath the flank of the salt dome. To avoid these potential drilling problems
(Bourgoyne at al., 1991)
in the salt, a directional well can be used to drill alongside the diapir (not vertically down through it) and then at an angle below the salt to reach the reservoir.
Increase the length of the "pay zone" within the target rock unit. If a rock unit is 50 ft thick, a vertical well drilled through it would have a pay zone that is 50 ft in length. However, if the well is turned and drilled horizontally through the rock unit for 5000 ft, then that single well will have a pay zone that is 5000 ft long. This will usually result in a significant productivity increase for the well. When combined with hydraulic fracturing, horizontal drilling can convert unproductive shales into fantastic reservoir rocks. 13
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Improve the productivity of wells in a fractured reservoir. This is done by drilling in a direction that intersects a maximum number of fractures. The drilling direction will normally be at right angles to the dominant fracture direction. Geothermal fields in granite bedrock usually get nearly all of their water exchange from fractures. Drilling at right angles to the dominant fracture direction will drive the well through a maximum number of fractures. This is done by drilling in a direction that intersects a maximum number of fractures. The drilling direction will normally be at right angles to the dominant fracture direction. Geothermal fields in granite bedrock usually get nearly all of their water exchange from fractures. Drilling at right angles to the dominant fracture direction will drive the well through a maximum number of fractures. Some reservoirs have most of their pore spaces in the form of fractures. Successful wells must penetrate fractures to have a flow of natural gas or oil into the well. In many geographic areas there is a dominant fracture direction along which most of the fractures are aligned. If the well is drilled perpendicular to the plane of these fractures, then a maximum number of fractures will be penetrated. Relief wells Drilling.
Involves directionally drilling a well into the blowout (wild) well when the surface location is no longer accessible, a very small target and takes specialized equipment. If a blow-out occurs and the rig is damaged, or destroyed, it may be possible to kill the “wild” well by drilling another directionally drilled well (relief well) to intercept or pass within a few
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
feet of the bottom of the “wild” well. The “wild” well is killed by circulating high density fluid down the relief well, into and up the wild well.
(Bourgoyne at al., 1991)
Relief well planning, design and drilling have been studied, researched, published and presented in many papers because the technique (relief well drilling) can be a critical safety measure, ensuring readiness and rapid response in the event of a catastrophic blowout that threatens human life, loss of drilling structures and facilities and harm to the environment (Vanessa Flores, 2014). Some few publications include (Kristoffer Evensen et al., 2014; Kallhovd, A. 2013; Roger B. Goobie et al., 2015; Rodrigo Varela et al., 215; Barnett, D. 2002; Flores, V., Dailey, P., Todd, D. et al., 2014; Goobie, R. 2013; Ng, Fred. 2010; ) According to Barnett, 2002, the objective of the directional well design is constrained by parameters required to deliver the necessary hydraulic force and capacity to satisfy the kill plan at the proper location. Near-parallel, low-incident-angle intercepts and reentry designs are possible. The design architecture of the relief well plan can become challenging because of the ellipse of uncertainty (EoU) associated with the survey program of both the blowout well and the relief well.
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
A relief well provides a means to intercept and kill a blowout well when surface intervention or capping requires an extended period of time or when such a procedure might not succeed (Ng 2010) A relief well is usually planned as a last resort option in the event the blowing wellbore is inaccessible and the rates required to kill the well are too large for surface intervention methods. See the example below where a drilling rig drills the relief well to intercept the blowout well as deep as necessary or to intercept at the last casing shoe before the hydrocarbon-bearing zone is encountered.
Figure 5 Relief Well Directional Designing (Flores et al. 2014)
2.2.Types of Directional Wellbore Profiles / Trajectories Depending on the penetration requirements there are three different overall profiles / trajectories of the well, namely Build-and-hold, Build-hold-and-drop also known as S-shaped, and, Continuous build (Mitchell, R. F., & Miska, S., 2011). These are shown in Figure 6 a, and b below.
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
a. (Mitchell, R. F., & Miska, S., 2011)
b. (Farah Omar 2013) Figure 6 Most common types of directional wellbore profiles
In practice, these generic shapes will be modified by local conditions. Getting the right well path is a multidisciplinary task in which geologists advise the designer about: The presence of faults, The precise shape of salt formations, Mud diapirs, and, Other subsurface hazards. Understanding the interaction between the 3D well trajectory and the formation stresses, particularly in overthrust areas, is vital to ensuring that the well can be drilled safely and efficiently. 17
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Many mathematical models for these types of trajectories are presented across some drilling technology texts (Bourgoyne Adam T, 1986; Rogers and W. M. Hole, 2000; Stromhaug Andreas Holm, 2014; Eustes III Alfred W, 2001, and Evers Jack F., 1984). a. Build-and-hold (slant) Well Trajectory A build-and-hold profile is the most common and simplest. It is planned so that the initial deflection angle is obtained at a shallow depth, and from that point on the angle is maintained as a straight line to the target zone. Once the angle and deflection are obtained, casing may be set through the deviated section and cemented. Generally, the build-and-hold profile is the basic building block of extended-reach drilling (ERD) wells. They can usually be employed in two distinct depth programs. These profiles can be used for moderate-depth drilling in areas where intermediate casing is not required and where oil-bearing strata are a single horizon. They can also be used for deeper wells requiring a large lateral displacement. In this case, an intermediate-casing string can be set to the required depth, and then the angle and direction can be maintained after drilling out below the string. b. Build-hold-and-drop (S-shaped) well trajectory The main reasons for drilling an S-shaped well are completion requirements for the reservoir; for example, when a massive stimulation operation is required during the completion. An S-shaped well also sets the initial deflection angle near the surface. After the angle is set, drilling continues on this line until the appropriate lateral displacement is attained. The hole is then returned to vertical or near vertical and drilled until the objective depth is reached. Surface casing is set through the upper deviated section and cemented. The wellbore is then continued at the desired angle until the lateral displacement has been reached and then returns to vertical. Intermediate casing is set through the lower vertical-return section. Drilling then continues below the intermediate casing in a vertical hole.
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
The S-shaped well is often employed with deep wells in areas where gas troubles, saltwater flows, etc. dictate the setting of intermediate casing. It permits moreaccurate bottomhole spacing in a multiple-pay area. The deflection angle may be set in surface zones in which drilling is fast and round-trip costs can be held to a minimum. c. Continuous-build (J) Well Trajectory A continuous-build well starts its deviation well below the surface. The angle is usually achieved with a constant build to the target point. The deflection angles may be relatively high, and the lateral distances from vertical to the desired penetration point are relatively shorter than other well types. Typical applications would be in exploring a stratigraphic trap or obtaining additional geological data on a noncommercial well. Because deflection operations take place deep in the hole, trip time for such operations is high, and the deflected part of the hole is not normally protected by casing. The continuous-build profile may also commonly be found in old fields in which development of bypassed oil is carried out by means of sidetracks from existing wells that have ceased to produce economically from the original completion. 2.3.How to Plan Directional Well Profile The first step in planning a directional well is to design the wellbore path or trajectory, to intersect a given target. The initial design should consider the various types of paths that can be drilled economically. To successfully plan a directional wellbore trajectory, it is important to determine the parameters defining the well path, understand the target and geography of the location, and finally define the well path.
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
2.3.1. Parameters defining the well path There are three specific parameters which must be considered when planning a well trajectory. These parameters which combine to define the trajectory of the well include: Kick-off point, Build-up and drop off rate (in degrees of inclination), Tangent angle of the well (or drift angle). Kick-off Point (KOP) - Is the long hole measured depth at which a change in inclination of the well is initiated and the well is oriented in a particular direction (in terms of north, south, east and west). In general, the most distant targets have the shallowest KOPs in order to reduce the inclination of the tangent section of the well (Figure 3). It is generally easier to kick off a well in shallow formations than in deep formations. The kick-off should also be initiated in formations which are stable and not likely to cause drilling problems, such as unconsolidated clays. Build-up and drop off rate (in degrees of inclination) - Are the rates at which the well deviates from the vertical (usually measured in degrees per 30 m or 100 ft). The build-up rate is chosen on the basis of previous drilling experience in the location and the tools available, but rates between 1° and 3° per 30 m or 100 ft of hole drilled are most common in conventional wells. Since the build- up and drop off rates are constant, these sections of the well, by definition, form the arc of a circle. Build up rates in excess of 3°/30 m are likely to cause doglegs when drilling conventional deviated wells with conventional drilling equipment. The build-up rate is often termed the dogleg severity (DLS). Tangent angle of the well (or drift angle) - Is the inclination (in degrees from the vertical) of the long straight section of the well after the build-up section of the well. This section of the well is termed the tangent section (the section of a well where the 20
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
well path is maintained at a certain inclination, with the intent of advancing in both TVD and vertical section. Short tangential sections are built for housing submersible pumps for example) because it forms a tangent to the arc formed by the build-up section of the
well. The tangent angle will generally be between 10° and 60° since it is difficult to control the trajectory of the well at angles below 10° and it is difficult to run wire line tools into wells at angles greater than 60°. Apart from these three specific parameters, there are other parameters which are also important to understand and here are some of them and their definitions: Azimuth - The angle (°) between the North direction and the plane containing the vertical line through the wellhead and the vertical line through the target. Displacement - The horizontal distance between the vertical lines passing through the target and the wellhead. Inclination - Angle (°) made by the tangential section of the hole with the vertical. Measured depth (MD) – The depth (length) of the well along the well path True-vertical depth (TVD) – The vertical distance between Kelly bushing (KB) and survey point. Vertical Section (VS) - Pre-defined azimuth angle along which the VS is calculated, usually the angle between north and a line uniting the wellhead and the total depth, measured on a plan view. Well path - The trajectory of a directionally drilled well in three dimensions.
2.3.2. Target and Geography of the Location The trajectory of a deviated well must be carefully planned so that the most efficient trajectory is used to drill between the rig and the target location and ensure that the well is drilled for the lowest cost. When planning, and subsequently drilling the well, the position of all points along the well-path trajectory is considered in three dimensions as shown in Figure 7 below. 21
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Figure 7: Well planning reference systems This means that the position of all points on the trajectory must be expressed with respect to a three dimensional reference system. The three dimensional system that is generally used to define the position of a particular point along the well path is (i) The vertical depth of the point below a particular reference point, (ii) The horizontal distance traversed from the wellhead in a northerly direction, and (iii) The distance traversed from the wellhead in an easterly direction. The depth of a particular point on the well path, referred to as true vertical depth (TVD) is expressed in meters (feet) vertically below a reference (datum) point. The northerly and easterly displacement of the point horizontally from the wellhead is reported as Northing/easting or longitude/latitude. Target design is an important element in planning wells. It is a multidisciplinary and interactive process between geoscientists, reservoir/production engineers and drilling engineers to define the combined uncertainty constraining the size of the target. A methodology and tool for target analysis and quantification of target intersection probability based on drilling and geological input has been developed to promote interdisciplinary communication and help designing realistic drilling targets (Ivar Haarstad, Oddvar Lotsberg, Torgeir Torkildsen, and Per Kristian Munkerud, 2002). 22
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
2.3.3. Defining the well path Having fixed the target and the rig position, the next stage is to plan the geometrical profile of the well to reach the target. The most common well trajectory is the build and hold profile, which consists of 3sections - vertical, build-up and tangent. The trajectory of the wellbore can be plotted when the following points have been defined: KOP kick-off point (selected by drilling engineer); TVD and horizontal displacement of the end of the build-up section; and TVD and horizontal displacement of the target (defined by the position of rig and target). Since the driller will only be able to determine the long hole depth of the well, the following information will also be required: A long hole depth (AHD) of the KOP (same as TVD of KOP); Build up rate for the build-up section (selected drilling by engineer); Direction in which the well is to be drilled after the KOP in degrees from north (defined by position of rig and target); AHD at end of build (EOB) and the tangent section commences; and AHD of the target. These depths and distances can be defined by a simple geometrical analysis of the well trajectory. 2.4.Illustrations Showing Calculations for the Well Paths (Trajectories) This section consists of calculations involving the different parameters of the types of directional wellbore profiles / trajectories discussed in section 2.2.i.e. Build-and-hold (slant - type), Build-hold-and-drop (S-type), and Continuous build (J-type).
23
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
2.4.1. Build-and-hold (Slant) Well Trajectory It is important to have in hand, the planning information required to design the well. Having received the wellhead (Surface “slots” coordinates), Target coordinates and Total Vertical Depth (TVD) of the target from the geologist or reservoir engineer, the following further information is needed in order to calculate the well trajectory. i.
True vertical depth to KOP;
ii.
Build-up-rate.
The choice of slot depends on a number of factors including target location and the proximity of other wells. The target coordinates and depth are selected by the geologist. The choice of KOP and build-up rate has to be made by the directional engineer (Bourgoyne, at al., 1991): After having decided upon a kick-off point (KOP) and build up rate, we can then determine the following parameters for the trajectory: 1. Angle at the end of build, 2. Measured depth at the end of build (MDEOB), 3. Vertical depth at the end of build, 4. Displacement at the end of build, 5. Measured depth to target One of the important steps in the process is to determine the radius of curvature (R) of a circle produced by the buildup rate. Radius of curvature (R) The circumference of a circle (C) produced by a constant change in direction for distance travelled is given by: C=
360 𝑞𝑞
……………….………………………………………………….. 1
Where q = rate of change = buildup rate But circumference of a circle, 24
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
C = 2𝜋𝜋R …………………….………………...…………………………… 2 Thus, R=
𝐶𝐶
2𝜋𝜋
………………………………………………………………………3
Putting eqn.1 into eqn.3 we have: R=
380 𝑞𝑞
x
1
2𝜋𝜋
=
180 𝑞𝑞𝑞𝑞
…………………………………………………………4
R = Radius of curvature.
Consider figure 8 below:
Angle of build
Figure 8 Illustration for Build-and-hold well trajectory calculation
25
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
From figure 8 above, DC = H2 – R …………………………………………………………………5 DO = V3 – V1………………………………..……………………………….6 Angle DOC = Tan-1 ( OC =
DO
Cos DOC
DC
DO
)…………………………………………………...…7
………………………………………….………………………8 R
Angle BOC = Cos-1 ( ) …………………………..…………………………9 OC
Angle BOD = Angle BOC – Angle DOC ………………...…………………10 And, ∝= 900 – angle BOD ………………………………………………….……..11
Then, from Pythagoras theorem we get BC,
BC = √𝑂𝑂𝑂𝑂 2 − 𝑅𝑅2 ……………………………………………………………12
BE = BC x Cos ∝ ……………………………………………………………13 EC = BC Sin ∝ .........................................................................................…...14
After having obtained different components in the profile figure, the parameters for the build-and-hold (slant - type) trajectory can be determined as follows: 1. Angle at the end of build = ∝
2. Measured depth at the end of build (MDEOB) = V1 + 3. Vertical depth at the end of build = V3 - BE 4. Displacement at the end of build = H1 = H2 - EC ∝
5. Measured depth to target = V1 + + BC 𝑞𝑞
26
∝ 𝑞𝑞
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
2.4.2. Build-hold-and-drop (S-type) Well Trajectory If we have in hand, the wellhead (Surface “slots” coordinates), target coordinates and Total Vertical Depth (TVD) of the target from the geologist or reservoir engineer, the following further details is needed in order to calculate the Build-hold-and-drop (Stype) well trajectory. i.
True vertical depth to KOP;
ii.
Build-up-rate.
iii.
Drop off rate (which was not needed for the slant – type well trajectory),
iv.
Vertical depth to the end of drop off (which also was not applicable for the slant – type well trajectory).
These points are decided upon based on the previous design considerations. Then, after having decided upon these criteria, we can calculate for the build-hold-and-drop well trajectory, the following parameters: I. II.
Angle at the end of build section, Measured depth at the end of build (MDEOB),
III.
Vertical depth at the end of build,
IV.
Displacement at the end of build,
V.
Measured depth at the start of drop off
VI.
Vertical depth at the start of drop off
VII.
Displacement at the start of drop off
VIII.
Measured depth at the end of drop off
It should be noted that, it is not necessary to return the well to vertical, however, if this is the case, the final inclination must be given. Consider figure 9 below for illustration.
27
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Figure 9 Illustration for Build-hold-and-drop well trajectory calculation From figure 9 above, X = H3 – (R1 + R1)………………………………… ……………………15 Angle𝜃𝜃: θ = Tan-1(
X
V4−V1
) …………………………………………………………16 28
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
OF =
V4−V1 Cos θ
………………………………………………………………..17
OG = �𝑂𝑂𝑂𝑂 2 − (𝑅𝑅2 + 𝑅𝑅1 )2 ………………………………………………..18
Angle FOG:
FOG = Sin-1(
R2 + R1 OF
) ………………………………………………………. 19
∝ = FOG + 𝜃𝜃 ……………………………………………………………….20
Again, after having obtained different components in the profile figure, the parameters for the build-hold-and-drop (S - type) well trajectory can be determined as follows: I. II.
Angle at the end of build section = ∝
Measured depth at the end of build (MDEOB) = V1 +
∝ 𝑞𝑞
III.
Vertical depth at the end of build = V2 = V1 + R1Sin∝
IV.
Displacement at the end of build = H1 = R1(1 - Cos∝)
V.
Measured depth at the end of tangent section and start of drop off = ∝
V1 + + OG VI.
𝑞𝑞
Vertical depth at the end of tangent section and start of drop off = V3= V2 + OG*Cos∝
VII.
Displacement at the end of tangent section and start of drop off = H2 = H1 + OG*Sin∝
VIII.
Measured depth at the end of drop off = V1 +
𝑞𝑞𝐵𝐵𝐵𝐵𝐵𝐵 = Build up rate 𝑞𝑞𝐷𝐷𝐷𝐷𝐷𝐷 = Drop off rate
29
∝
𝑞𝑞 𝐵𝐵𝐵𝐵𝐵𝐵
+ OG +
∝
𝑞𝑞 𝐷𝐷𝐷𝐷𝐷𝐷
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
2.4.3. Continuous-build (J) Well Trajectory Suppose we have in hand, the wellhead (Surface “slots” coordinates), target coordinates and Total Vertical Depth (TVD) of the target from the geologist or reservoir engineer, either or any of the following further information is required in order to calculate the Continuous - build (J-type) well trajectory parameters: i.
True vertical depth to KOP;
ii.
Build-up-rate, Or
iii.
Maximum angle desired.
After having decided upon which is the most critical factor involved, the other variables are then made to fit the conditions and the J – Type well trajectory may be calculated to determine: a) Final angle if not the controlling factor, b) Rate of build up required, c) Kick off point (KOP)
Figure 10 Illustration for Continuous-Build (J-Type) well trajectory calculation 30
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Case 1: If the buildup rate (q) is established, then: R 1 −H 1
Maximum angle, ∝ = Cos-1(
R1
)
Kick off point (KOP) = V2 – R1Sin∝ Case2: If the kick off point is chosen as the criteria, then: ∝ = 2Tan-1(V
H1
2 −V 1
)
Build up rate required, q = drilled).
180 Sin ∝
π(V 2 −V 1 )
expressed in (per unit meters of feet
3. PRACTICAL APPLICATION OF WELL TRAJECTORY DESIGNING THROUGH CASE STUDIES 3.1.Case Study 1 In figure 11 (Jones et al, 2008) provides an example of a planned well profile, from a plane view and a vertical view. This is a relatively simple directional well, which was designed to hit two targets, as shown by the boxes on the plan view. The easiest type of directional well profile is a so-called “J-shaped profile”, which is a continuousbuild to the target. The target in this case was an area, rather than a single point, and the well need not therefore to hit the center of the target. Although it was possible to hit small targets, this increase in accuracy comes with a higher financial cost. In Figure 6, the lower target will be hit on the edge nearest to the surface location.
31
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Figure 11 J Profile Directional well plan (Jones et al., 2008)
3.2. Case Study 2: “Well Asal 5: An example of a well profile in the Asal Rift Geothermal Field (Reykjavik Energy Invest (REI), 2009)” Well Asal-5 (Figure 12) is the deepest well (2105 m) drilled in the Asal Rift and is unproductive as it penetrates both cold and hot formations. Data from this well (Árnason and Flóvenz, 1995) indicate a possible shallow hot reservoir (160°C) at 500550 m depth, then a cold zone (about 60°C) down to 1200 m depth. Below 1200 m, temperature increases and the bottom temperature is about 333°C at 2105 m. The well has never been discharged. This temperature profile suggests firstly that there are active flow channels of fresh seawater recharging a deep reservoir. Secondly, the downhole high temperature confirms a large heat reserve. After the well became unsuccessful, Icelandic scientists familiar with the strategic research of 32
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
similar geothermal fields joined the exploration of Asal Geothermal Field. The geological investigations of the Asal Field (Saemundsson, 1988) indicated that Well Asal-5 was not correctly sited as it would be about 700-1000 m from the geothermal up flow zone. Shortly thereafter, resistivity studies were undertaken using the TEM method (Transient Electromagnetics) in the Inner Rift (Árnason et al., 1988). The survey indicated the existence of an up flow zone of geothermal fluid under the Lava Lake, as had been mentioned by Saemundsson (1988). These results showed this area to be the most promising for future exploratory wells.
Figure 12 Temperature profile, geology, thermal alteration and TEM based resistivity model for well 5 (modified from Árnason and Flóvenz, 1995) The build-and-hold Asal 5 Well Trajectory Calculation In Asal 5 well, the idea was to drill under the Lava Lake to the locations designated as the four targets. For these wells, a build-and-hold trajectory was used. Horizontal departure to the target zone is 1015 m at a TVD of 2247.2 m. The recommended rate of build is 3°/30 m. The kick-off depth is 350 m. The following parameters can be determined for the well trajectory. 33
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
1. The radius of curvature, R; 2. The maximum inclination angle, ∝
3. The measured depth to the end of the build; 4. The total depth measured; 5. The horizontal departure to the end of the build. Data given: Target zone coordinates N120° or N325° (two propositions) N100° N165°
Well AA Well AB Well AC -
Horizontal departure to the target zone (H2) = 1015 m
-
Total Vertical Depth to target (TVDTgt) = 2247.2 m.
-
The recommended rate of build (q) = 3°/30 m.
-
The kick-off depth (TVDKOP) = 350 m
-
R=
380 𝑞𝑞
x
1
2𝜋𝜋
=
180 𝑞𝑞𝑞𝑞
=
180 𝜋𝜋
x
1
3⁄30
=
180 𝑥𝑥30 3𝜋𝜋
34
= 572.96 m
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
Figure 13 Geometry of Asal 5 Well build-and-hold Trajectory (manual sketch) Data analysis: From figure 13 above;
H1 = Horizontal departure to the end of buildup =? H2 = Horizontal displacement to the target = 1015 m (given) R= Radius of curvature = 572.96 m (calculated) V1=TVDAB = TVDKOP = Total Vertical Depth to Kick-Off Point = 350 m (given) V2=TVDAC = TVDEOB = Total Vertical Depth to the end of build up =? V3=TVDAG = TVDtgt = Total Vertical Depth to the target = = 2247.2 m (given) ���� 𝐸𝐸𝐸𝐸 = H2 – R = 1015 - 572.96 = 442.04 m ���� 𝐸𝐸𝐸𝐸 = V3 – V1 = 2247.2 – 350 = 1897.6 m 35
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
𝐸𝐸𝐸𝐸 442 .04 � D = Tan-1(���� EO ) = Tan-1( ) = 13.11o ���� 𝐸𝐸𝐸𝐸
���� ���� = 𝐸𝐸𝐸𝐸 𝑂𝑂𝑂𝑂 = 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 𝑂𝑂� 𝐷𝐷
1897 .6
𝐶𝐶𝐶𝐶𝐶𝐶13.11
1897 .6
= 1948.38 m
� D = Cos-1( 𝑅𝑅 ) = Cos-1( 572 .96 ) = 72.89o CO ���� 𝑂𝑂𝑂𝑂
1948 .38
� E = CO � D - EO � D = 72.89o - 13.11o = 59.78o CO � E = 90o - 59.78o = 30.22o ∝ = 90o - CO
���� 𝐶𝐶𝐶𝐶 = ����� 𝑂𝑂𝑂𝑂 2 − ���� 𝐶𝐶𝐶𝐶2 = ����� 𝑂𝑂𝑂𝑂 2 − 𝑅𝑅2 = √1948.382 − 572.962 = 1862.23 m ���� 𝐹𝐹𝐹𝐹 = ���� 𝐶𝐶𝐶𝐶 . Sin∝ = 1862.23 x Sin 30.22o = 937.30 m
Finally, the Parameters of the Asal 5 Well build-and-hold Trajectory are: 1. The radius of curvature, R = 572.96 m 2. The maximum inclination angle, ∝ = 30.22o
3. The measured depth to the end of the build (MDEOB) = ∝
30.22
V1 + = 350+ 3 𝑞𝑞
�30
= 652.2 m
4. The total depth measured (MDTgt) = ∝
30.22
���� = 350+ 3 V1 + + 𝐶𝐶𝐶𝐶 𝑞𝑞
�30
+ 1862.23 = 2514.43 m
���� = 5. The horizontal departure to the end of the build (H1) = 𝐺𝐺𝐺𝐺 ���� = 1015 - 937.30 = 77.7 m H2 - 𝐹𝐹𝐹𝐹
36
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
3.3. Advantages of the Build-and-hold (Slant) Well Trajectory Following a thorough review of different research literatures, amongst the three types of trajectories discussed in this report, the Build-and-hold (Slant) method has several advantages: Opting for the nearest edge allows the well to be built to a lower inclination, and therefore not as much hole needs to be drilled. Should the well fail to build angle at a fast enough rate, then it could end up missing its target. However, a higher build rate does not have a negative effect on the drilling rate of penetration (ROP). On the other hand, reducing the angle to reach the target will mean compromising the drilling rate. This is caused by the fact that decreasing the angle usually requires removing weight from the bit. However, this does not apply to all tools, for example, some tools such as rotary steerable tools, are exempt from this problem, although come at a higher financial cost. Unless the drilling operation already has a high daily cost, rotary steerable tools would not normally be used to correct a directional issue. If the low edge is aimed at, then directional correction work will not have a negative impact on drilling speed. Other factors need to be taken into consideration when planning a well path. Whenever the well changes direction, the drillpipe needs to bend around that curve, and if the well is curved when still near the surface, this curve will cause additional drillpipe tension the deeper the well gets and the more weight is put on the drillpipe. This additional side force can cause numerous problems, including metal fatigue or wear on the pipe, and may even cause the pipe to become completely stuck.
37
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
4. CONCLUSION Even though planning and designing a directional well trajectory / or path involves both survey calculations “for determining the grid points for the targets to be traversed by the well such as North – East, South – West coordinate angles” and well trajectory calculations “for determining KOP, inclinations, TVDs to KOP, End of Build (EOB), Horizontal departure to EOB and to target and many other parameters, this report focused solely on Directional well planning and design of the well trajectory where three types of trajectories namely: Build-and-hold (slant type), buildhold-and-drop (S-type), and continuous-build (J-type) were discussed and formulae for calculations were also derived together with some practical examples of case studies. The survey calculations methods commonly used in survey calculations such as Average angle; Tangential; Balanced tangential (rarely used); Radius of curvature; and Minimum curvature, were not part of this report. The foregoing approaches are only a few of the possibilities that could be deduced from the principles of directional drilling presented in this report. Even though the build-and-hold approach has some advantages as stipulated in section 3.3 of this report, there is no absolute way of drilling a directional well. However, there are better, optimal ways to drill any well (good planning and careful selection of the bit, mud system, etc.) that should minimize the risks. Considering the previous results (trajectory and survey calculations), with REI’s proposal to make the KOP at 350 m, it is proposed here that the kick off point should be at least 30 meters below the casing shoe. Thus, all directional wells in the future in Asal should have a kickoff point at 430 m depth at least with a 400 m intermediate casing. Vertical drilling can be used as another option since all subsurface information can be gathered by either vertical or directional drilling. The choice of drilling method depends mostly on the cost, for which a thorough cost estimate of: (a) survey tools and equipment for directional drilling, (b) multiple well pads, and (c) drilling, will determine whether vertical or directional drilling is the better option.
38
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
REFERENCES 1. Baker, R. (2001). A Primer of Oil well Drilling :A Basic Text of Oil and Gas Drilling. Univ. of Texas at Austin, Petroleum Extension Service, Texas, USA, 6thedition. 2. Barnett, D. 2002. Relief well drilling operations allows re-entry and control of blowout well. World Oil 223 (1). 3. Bourgoyne Adam T. Jr., Millheim Keith K., Chenevert Martin E., Young F. S. Jr. Applied Drilling Engineering. Society of Petroleum Engineers, Richardson,. Texas, pp. 351-66. 1986. 4. Eustes III Alfred W. Directional Drilling Seminar. Colorado school of mines Golden, , Colorado. 2001. 5. Evers Jack F. Directional drilling and deviation control. Applied Drilling Engineering, , 19th printing. (1984). 6. Flores, V., Dailey, P., Todd, D. et alet al. 2014. Relief Well planning. Presented at the IADC/SPE Drilling Conference and Exhibition, Fort Worth, Texas, USA, 4-6 March. SPE-168029-MS. 7. Gabolde, G., and Nguyen, J.P., 1991: Drilling data handbook. Gulf Publising Co., Houston, TX, United States, 542 pp. 8. Goobie, R. 2013. BP Quick Guidelines for Relief Well Designs. Presented at the SPE Collision Avoidance and Wells Interceptions Hit and Misses Workshop, 6 November. 9. Gruenhagen, H., Hahne, U., & Alvord, G. (2002, January 1). Application of New Generation Rotary Steerable System for Reservoir Drilling in Remote Areas. Society of Petroleum Engineers. 10. http://www.glossary.oilfield.slb.com/Terms/g/geosteering.aspx 11. Jones, S., & Sugiura, J. (2008, January 1). Concurrent Rotary-Steerable Directional Drilling and Hole Enlargement Applied Successfully: Case Studies in North Sea, Mediterranean Sea, and Nile Delta. Society of Petroleum Engineers 12. Joshi, S.D., 2003. “Cost / benefits of horizontal wells”, 2003 (SPE paper 83621). 13. Kallhovd, A. 2013. Evaluation of a dual relief well operation. MS thesis. NTNU - Trondheim, Norwegian University of Science and Technology, June 2013. 39
Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
14. Khaled, A/El, Fattah, S., El-Tayeb, A., Dahab, A., Khalaf, F., 1999. “3-D well design using computer optimization model”. In: 4th Computer Conference, SPE Egypt Section. 15. Khodayar, M., 2008: Results of the 2007 surface geothermal exploration in the Asal Rift and transform zones, Djibouti: Tectonics and geothermal manifestations (revised version, May 2008). Iceland GeoSurvey, report ÍSOR2008/008, prepared for REI (confidential), 81 pp + 5 maps. 16. Kuwana, S., Kiyosawa, Y., and Ikeda, A. (1994). Attitude control device and drilling-direction control device. 17. Li, A., Feng, E., and Gong, Z. (2009). An optimal control model and algorithm for the deviated well’s trajectory planning. Applied Mathematical Modeling, 33(7), 3068–3075. 18. Martin et al., 2017 “ Directional Drilling Attitude Control with Input Disturbances and Feedback Delay”, IFAC PapersOnLine 50-1 (2017) 1409– 1414 19. Mitchell, R. F., & Miska, S. (Eds.) (2011). “Fundamentals of Drilling Engineering”. Richardson, TX: Society of Petroleum Engineers. SPEBookstore and WorldCat 20. Ng, Fred. 2010. An Introduction to Relief Well Planning, Dynamic Kill Design: Recognizing the Common Limitations. Drilling Contractor, November 2010. 21. P. O. Okpozo, A. Peters, and W. C. Okologume, 2016 “Directional Well Trajectory Design: The Theoretical Development of Azimuth Bends and Turns in Complex Well Trajectory Designs”, Nigerian Journal of Technology (NIJOTECH), Vol. 35, pp. 831 – 840 22. REI, 2009: Geothermal pre-feasibility study in the Asal Rift, Djibouti: Project status after completions of surface exploration studies and environmental impact assessment. Reykjavik Energy Invest, confidential report, REI-2008, 20 pp. 23. REI, 2008: Drilling and testing of geothermal exploration wells in the Assal Area, Djibouti: Environmental management plan. Reykjavik Energy Invest, report REI-2008/Asal 1, 58 pp. 24. Rodrigo Varela et al., 2015 Multiple Relief Well Planning for an HPHT Blowout in Southern Mexico. SPE/IADC – 173160 – MS
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Directional Well Planning and Trajectory Design Calculations Modern Drilling Technology – Class Report Zahoro Athumani, CUG
25. Roger B. Goobie et al., 2015 “A Guide to Relief Well Trajectory Design using Multidisciplinary Collaborative Well Planning Technology”, SPE/IADC173097-MS 26. Rogers, W. M., 2000 “Hole Deviation and Horizontal Drilling. IADC drilling manual, eleventh version”, 2000. 27. Saemundsson, K., 1988: Djibouti geothermal project. Analysis of geological data pertaining to geothermal exploration of Asal rift. UNDP, 18 pp 28. Shengzong, J., Xilu, W., Limin, C., and Kunfang, L. (1999). “A new method for designing 3-D trajectory in sidetracking horizontal wells under multiconstraints” In SPE Asia Pacific Improved Oil Recovery Conference. Kuala Lumpur, Malaysia 29. Sperry-Sun, 2001: Directional surveying fundamentals. Sperry-Sun Training Department, a Halliburton Company, Houston, TX, United States, 108 pp. 30. Stromhaug Andreas Holm, 2014. “Directional Drilling – Advance Trajectory Modeling”. Published Masters’ Thesis, NTNU – Trondheim Norwegian University of Science and Technology, 2014. 31. Tetsuo et al., (2002). Robotic controlled drilling: A new rotary steerable drilling system for the oil and gas industry. In IADC / SPE Drilling Conference. Texas, USA. 32. Upchurch, E.R., 2015; Geo-Stopping Using Deep Directional Resistivity LWD: A New Method for Well Bore Placement Using Below-the-Bit Resistivity Mapping; paper SPE/IADC 173169 33. Varela, R. et al., 2015: Multiple Relief Well Planning for an HPHT Blowout in Southern Mexico; paper SPE/IADC 173160 34. Warriner, et al., 1988; Relief-Well Requirements to Kill a High-Rate Gas Blowout from a Deepwater Reservoir; SPE 16131 35. Williams, S. (2010). Geosteering: Where are we? Where are we going? In EAGE Geosteering and Well Placement Workshop: Balancing Value and Risk. Dubai, UAE. 36. Willson, et al., 2012; A Wellbore Stability Approach For Self-Killing Blowout Assessment; paper SPE 156330 37. Wright, J., 2014 Relief Well Plan for a Cratered Well, http://www.jwco.com/relief_well_plan_cratered-_well.htm (accessed September 2014). 38. Xiang Wu and, Kanjian Zhang, 2015 “Three-dimensional trajectory design for horizontal well based on optimal switching algorithms”, ISA Transactions58 (2015)348–356 41
