WO2025254968A1

WO2025254968A1 - Determining a drilling path in a subterranean formation

Info

Publication number: WO2025254968A1
Application number: PCT/US2025/031757
Authority: WO
Inventors: Ala Edeen Herzallah; Atallah N. ALHARBI; Faisal Khalid A. ALSWAILEM; Meshari M. Alshalan; Jr. James H. Taylor; Wael ALZIADAT; William Schultz; Albert Odell
Original assignee: Saudi Arabian Oil Co; Aramco Services Co; Weatherford Technology Holdings LLC
Current assignee: Saudi Arabian Oil Co; Aramco Services Co; Weatherford Technology Holdings LLC
Priority date: 2024-06-06
Filing date: 2025-05-30
Publication date: 2025-12-11
Anticipated expiration: 2026-12-06
Also published as: US20250376897A1

Abstract

A downhole tool includes a milling assembly configured to couple to a tubular string and run into a vertical wellbore formed from a terranean surface to one or more subterranean formations. The milling assembly includes a tubular mandrel; a first mill coupled to the tubular mandrel at a downhole end of the tubular mandrel; and a second mill coupled to the tubular mandrel uphole of the first mill. The downhole tool includes an inclination sensor mounted in or to the tubular mandrel between the first mill and the second mill. The inclination sensor is configured to determine an angle between a lateral wellbore formed by the milling assembly from a window in the vertical wellbore and the vertical wellbore.

Description

DETERMINING A DRILLING PATH IN A SUBTERRANEAN FORMATION

CLAIM OF PRIORITY

[0001] This application claims priority to U.S. Patent Application No. 18/736,072 filed on June 6, 2024, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

[0002] The present disclosure describes systems and methods for determining a drilling path in a subterranean formation and more particularly, determining a drilling path with a bottom hole assembly that includes a milling assembly that determines an angular drill path.

BACKGROUND

[0003] Whipstocks are wedges designed to anchor on an inside wall of a joint of casing and enable milling operations through the wall of the casing and into a subterranean formation. In the oil and gas drilling industry’, this operation is typically referred to as a casing exit operation or a cased-hole sidetrack. A successful casing exit operation requires creating a sideways hole, departing at an angle away from the inclination of the original casing string. This angular direction (or build up) is typically in the range of 2-3 degrees relative to the original casing string. If the buildup fails, the sidetrack hole ends up parallel to the original casing string (i.e.. right next to the casing string). Such a failure is called “casing tracking" and, when the drilling operations trips in hole again with the next drilling assembly to start drilling the rest of the well, the drill bit will start drilling against the metal casing string instead of drilling through the rock formation. This can result in damage to the casing string and to other components of the drilling assembly. The drilling operation is then forced to pull the drilling assembly out of hole, take remedial action, and use a new drilling assembly afterwards.

SUMMARY

[0004] In an example implementation, a downhole tool includes a milling assembly configured to couple to a tubular string and run into a vertical wellbore formed from a terranean surface to one or more subterranean formations. The milling assembly includes a tubular mandrel: a first mill coupled to the tubular mandrel at a downhole end of the tubular mandrel: and a second mill coupled to the tubular mandrel uphole of the first mill. The downhole tool includes an inclination sensor mounted in or to the tubular mandrel between the first mill and the second mill. The inclination sensor is configured to determine an angle between a lateral wellbore formed by the milling assembly from a window in the vertical wellbore and the vertical wellbore.

[0005] In an aspect combinable with the example implementation, the inclination sensor is mounted within a pocket formed in a wall of the tubular mandrel.

[0006] Another aspect combinable with one, some, or all of the previous aspects includes a cover plate coupled to the tubular mandrel over the pocket to enclose the inclination sensor.

[0007] Another aspect combinable with one, some, or all of the previous aspects includes one or more fasteners configured to couple at least one of the inclination sensor or the cover plate to the tubular mandrel.

[0008] In another aspect combinable with one, some, or all of the previous aspects, the inclination sensor is configured to determine a first angle between the lateral wellbore formed by the milling assembly from the window in the vertical wellbore and the vertical wellbore; and a second angle between the lateral wellbore formed by the milling assembly from the window in the vertical wellbore and the vertical wellbore.

[0009] In another aspect combinable with one, some, or all of the previous aspects, the inclination sensor includes a printed circuit board that includes at least one accelerometer; and at least one memory' module communicably coupled to the at least one accelerometer.

[0010] Another aspect combinable with one. some, or all of the previous aspects includes a third mill coupled to the tubular mandrel uphole of the second mill.

[0011] In another example implementation, a drilling system includes a whipstock configured couple to a casing positioned in a vertical wellbore formed from a terranean surface to one or more subterranean formations; and a bottom hole assembly including a milling assembly configured to couple to a tubular string and run into the vertical wellbore through the casing. The milling assembly includes a tubular mandrel; a plurality of mills, each mill coupled to the tubular mandrel; and an inclination sensor mounted in or to the tubular mandrel between two of the plurality of mills. The inclination sensor is configured to determine an angle between a lateral wellbore formed by the milling assembly from a window in the vertical wellbore and the vertical wellbore.

[0012] In an aspect combinable with the example implementation, the inclination sensor is mounted within a pocket formed in a wall of the tubular mandrel.

[0013] Another aspect combinable with one, some, or all of the previous aspects includes a cover plate coupled to the tubular mandrel over the pocket to enclose the inclination sensor.

[0014] Another aspect combinable with one, some, or all of the previous aspects includes one or more fasteners configured to couple at least one of the inclination sensor or the cover plate to the tubular mandrel.

[0015] In another aspect combinable with one, some, or all of the previous aspects, the inclination sensor is configured to determine a first angle between the lateral wellbore formed by the milling assembly from the window in the vertical wellbore and the vertical wellbore; and a second angle between the lateral wellbore formed by the milling assembly from the window in the vertical wellbore and the vertical wellbore.

[0016] In another aspect combinable with one, some, or all of the previous aspects, the inclination sensor includes a printed circuit board that includes at least one accelerometer; and at least one memory' module communicably coupled to the at least one accelerometer.

[0017] In another aspect combinable with one, some, or all of the previous aspects, the plurality of mills include a first mill positioned at a distal end of the tubular mandrel and a second mill positioned uphole of the first mill.

[0018] In another aspect combinable with one, some, or all of the previous aspects, the inclination sensor is mounted in or to the tubular mandrel between the first and second mills.

[0019] In another example implementation, a drilling method includes running a downhole tool into a vertical wellbore formed from a terranean surface to one or more subterranean formations. The downhole tool includes a milling assembly that includes a tubular mandrel; a first mill coupled to the tubular mandrel at a downhole end of the tubular mandrel; a second mill coupled to the tubular mandrel uphole of the first mill; and an inclination sensor mounted in or to the tubular mandrel between the first mill and the second mill. The method includes urging the milling assembly through a window in a casing of the vertical wellbore with a whipstock positioned in the vertical wellbore; milling at least a portion of a lateral wellbore from the w indow : and during the milling, determining an angle between the lateral wellbore and the vertical wellbore with the inclination sensor.

[0020] In an aspect combinable with the example implementation, milling the portion of the lateral wellbore from the window' includes milling the portion of the lateral wellbore with the first and second mills.

[0021] Another aspect combinable with one. some, or all of the previous aspects includes installing the inclination sensor w ithin a pocket formed in a wall of the tubular mandrel.

[0022] Another aspect combinable w ith one, some, or all of the previous aspects includes securing the inclination sensor on or to the tubular mandrel with one or more tension bolts.

[0023] In another aspect combinable with one, some, or all of the previous aspects, determining the angle between the lateral wellbore and the vertical wellbore with the inclination sensor includes determining a first angle between the lateral wellbore and the vertical wellbore; and determining a second angle between the lateral w ellbore and the vertical wellbore.

[0024] In another aspect combinable with one, some, or all of the previous aspects, determining the angle between the lateral wellbore and the vertical wellbore with the inclination sensor includes determining the angle with at least one accelerometer.

[0025] Another aspect combinable with one, some, or all of the previous aspects includes storing the determined angle in at least one memory module communicably coupled to the at least one accelerometer; and subsequent to running the milling assembly out of the vertical wellbore to the terranean surface, accessing the stored determined angle from the at least one memory module.

[0026] Implementations of systems and methods for determining a drilling path according to the present disclosure may also include one or more of the following features. For example, implementations according to the present disclosure can allow- for placement of a near-mill sensor in milling assemblies to give a w ell operator an early indications on the success of casing exit operations, and an early warning on the failure of casing exit operations. As another example, implementations according to the present disclosure can therefore provide a milling process in which early remedial action can be taken when needed (if failures are detected) and unnecessary pre-cautionary runs are not performed when not needed (when milling success is confirmed). As another example, implementations according to the present disclosure can enable near-mill sensor placement safely and reliably in higher stress components, but also maintain the sensor as close to a mill downhole end for optimal readings.

[0027] The details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 is a schematic diagram of a drilling operation that can include a bottom hole assembly (BHA) with a milling sub-assembly according to the present disclosure.

[0029] FIG. 2 is a schematic diagram of an example implementation of a BHA with a milling sub-assembly according to the present disclosure.

[0030] FIG. 3 is a schematic diagram of an example implementation of an inclination sensor used in a BHA with a milling sub-assembly according to the present disclosure.

[0031] FIGS. 4A and 4B are schematic diagrams of an example implementation of portions of a BHA with a milling sub-assembly that includes an inclination sensor according to the present disclosure.

[0032] FIGS. 5A-5C are schematic diagrams of an example drilling operation using a BHA with a milling sub-assembly according to the present disclosure.

[0033] FIG. 6 is a schematic diagram of an angle between a sidetrack and a primary wellbore according to the present disclosure.

[0034] FIGS. 7-9 are graphs that illustrate test results for an inclination sensor used in a BHA with a milling sub-assembly according to the present disclosure.

DETAILED DESCRIPTION

[0035] The present disclosure describes example implementations of a milling assembly for a bottom hole assembly that includes one or more inclination sensors mounted between mills on the milling assembly, such as between a primary (for example, downhole most) mill and a secondary mill. During operation of the milling assembly, such as to form a window in a casing in a vertical wellbore and initiate a lateral wellbore, the inclination sensor(s) can measure angular displacement from the vertical wellbore to ensure that the sidetrack for the lateral wellbore is angled properly. [0036] FIG. 1 is a schematic diagram of a drilling operation 10 that can include a bottom hole assembly that includes a milling assembly according to the present disclosure. For example, drilling system 10 includes a drilling rig 2 configured to form a vertical wel Ibore 8 and one or more lateral wel Ibores 12 (from the vertical wellbore 8) from a terranean surface 4 (which can also be a body of water). The wellbores 8 and 12 extend from the terranean surface 4 into one or more subterranean formations 6. During drilling operations, as shown in the circular view, a bottom hole assembly (BHA) 14 that includes a drill bit 20 is operated through a casing 16 (for example, installed on the vertical wellbore 8) to form the laterals 12. During formation of the laterals 12, the drill bit 20 drills through the casing 16 with the help of a whipstock 18 to form a window' 19. The BHA 14 forms the laterals 12 from the respective windows 19 at an angle offset from the vertical wellbore 8. Once a portion of a lateral 12 has been formed at an appropriate angle (for example, 2-3 degrees) aw ay from the vertical wellbore 8, further drilling operations can commence to form the rest of the lateral 12.

[0037] FIG. 2 is a schematic diagram of an example implementation of the BHA 14 with a milling sub-assembly 200 according to the present disclosure. As shown in this example, the BHA 14 is run into the wellbore 8 and through production casing 16 to the whipstock 18. As shown in this example, the whipstock 18 is positioned uphole of a seal / slip assembly 30 that is anchored to the casing 16. The BHA 14, in this example, is coupled to a downhole conveyance 25, such as a drill string comprised of tubular sections coupled together.

[0038] In this example implementation, the milling sub-assembly 200 includes multiple mills mounted on or connected to a tubular mandrel 202 (that can be a single tubular section or multiple tubular sections). For example, a first or primary mill 204 is positioned on the tubular mandrel 202 at a downhole end of the milling sub-assembly 200. Separated from the primary mill 204 by a portion 203 of the tubular mandrel 202 is a second or secondary' mill 206. Optionally, and separated from the secondary' mill 206 by a portion 205 of the tubular mandrel 202 is a third or tertiary mill 208. In operation, the mills 204, 206, and (optionally) 208, can be operated with the BHA 14 to mill window 19 in the casing 16 and, through angular contact with the whipstock 18, initiate a lateral wellbore 12 that is angled from the vertical wellbore 8.

[0039] As shown in this example implementation, an inclination sensor 210 is positioned in or on the portion 203 of the tubular mandrel 202. In operation, during milling of the lateral 12 from the wellbore 8 (with the milling sub-assembly 200 angled by the whipstock 18), the inclination sensor 210 measures at least one angle between the lateral wellbore 12 and the vertical wellbore 8. In some aspects, the inclination sensor 210 can be activated at the surface (for example, activated in a memory mode) before the start of the milling operation by the BHA 14. The inclination sensor 210 provides angle readings to the measured inclination above the opened window 19 and at the bottom of the drilled lateral 12. The measured angular inclination readings can be stored in the inclination sensor 210 and, after a particular amount of milling time or length of milling performed by the BHA 14, the inclination sensor 210 (along with the BHA 14) can be run out of the wellbore 8 so that the stored readings can be obtained. If the measured inclination readings are correct, for example, 2-3 degrees, the continued milling or drilling operations are continued. If the measured inclination readings are small, such as near zero degrees inclination, this can indicate casing tracking and remedial operations are taken before running in the wellbore 8 with the next drilling assembly.

[0040] FIG. 3 is a schematic diagram of an example implementation of the inclination sensor 210 used in the BHA 14 with the milling sub-assembly 200 according to the present disclosure. In this example implementation, the inclination sensor 210 includes a housing 212 in which a printed circuit board (PCB) 214 is enclosed. In this example implementation, the PCB 214 includes at least one accelerometer 216 and a memory module 218. The accelerometer 216, in example aspects, measures the inclination angle between the lateral wellbore 12 and vertical wellbore 8.

[0041] In some aspects, the measured angle includes two measured angles. For example, turning briefly to FIG. 6, this figure shows a schematic diagram of an angle between the sidetrack (lateral 12) and a primary wellbore (vertical wellbore 8). As shown in this example, as the BHA 14 (including milling sub-assembly 200) is milling the lateral 12, the inclination sensor 210 can measure (for example, per time or milled distance) an angle 601 (in the x direction), an angle 602 (in the z direction), or both. [0042] As the measurement readings (of one or two angular deviations of the lateral 12 from the vertical wellbore 8) accumulate, the accelerometer 216 provides the readings to the memory module 218. The inclination angle readings are then stored in the memory module 218 (for example, as analog or digital data) until the BHA 14 is run out of the wellbore 8 and to the surface 4. On the surface 4, the memory⁷ module 218 can be interrogated or otherwise provide the stored inclination readings for analysis.

[0043] FIGS. 4A and 4B are schematic diagrams of an example implementation of portions of the BHA 14 with the milling sub-assembly 200 that includes the inclination sensor 210 according to the present disclosure. As shown in this example (and as shown in FIG. 2), the inclination sensor 210 is positioned in the tubular mandrel 202 adjacent the primary mill 204 (and between the primary mill 204 and the secondary⁷ mill 206). In this example, the inclination sensor 210 is inserted or otherwise positioned in a pocket 213 (or slot) that is milled in the w all 215 of the tubular mandrel 202. Once positioned in the pocket 213, a cover 230 can (optionally) be secured over the inclination sensor 210 to enclose the sensor 210 in the pocket 213.

[0044] FIGS. 5A-5C are schematic diagrams of an example drilling operation using the BHA 14 with the milling sub-assembly according to the present disclosure. For example, as shown in FIG. 5A, the whipstock 18 can be installed in a seal / slip assembly 30, which is anchored in the wellbore 8 (for example, to the casing 16). An orienting sub 21 coupled to a downhole end of the whipstock 18 allows the whipstock 18 to be secured in the seal / slip assembly 30 and angled so that the face of the whipstock 18 (on which the milling assembly 200 is run) is opposite a desired window location (for window- 19). In FIG. 5B, the whipstock 18 is secured in the seal I slip assembly 30 and the milling assembly 200 is in contact with a setting stud 17 on the whipstock 18, which helps orient the milling assembly 200 to mill window 19 in the casing 16 and start lateral wellbore 12. The mills 204 and 206 mill through the casing 16 and angle from the vertical w ellbore 8 to start the lateral wellbore 12. During the milling, the inclination sensor 210 measures the angle (or multiple angles) between the vertical wellbore 8 and the lateral wellbore 12. The measurements can be stored in the inclination sensor 210 and then analyzed when the BHA 14 is run out of the vertical wellbore 8 (after initiating the lateral w ellbore 12.

[0045] If the measurements of the angle between the vertical wellbore 8 and lateral wellbore 12 show a proper angle (for example, about 2-3 degrees), then a drilling assembly 300 can be run into the vertical wellbore 8 to finish the lateral wellbore 12 as shown in FIG. 5C. However, if the measurements of the angle between the vertical wellbore 8 and lateral wellbore 12 show an improper angle (too close to the vertical wellbore 8 or too far from the vertical wellbore 8), then the milling assembly 200 can be run back into the vertical wellbore 8 for remedial action.

[0046] FIGS. 7-9 are graphs that illustrate test results for an inclination sensor used in a BHA with a milling sub-assembly according to the present disclosure. For example, a prototype inclination sensor 210 was built and tested to validate: sensor output at controlled inclinations, and sensor functionality at a required or desired temperature range. FIG. 7 shows a graph 700 of measured rotations taken by the inclination sensor 210 over time. Graph 700 includes x-axis 702 of time (in hours, minutes, and seconds) and a y-axis 704 of rotation (in degrees). FIG. 8 shows a graph 800 of operation of the inclination sensor 210 to measure angular displacement at a temperature range between about 20-130°C over time. Graph 800 includes x-axis 802 of time (in hours, minutes, and seconds) and ay-axis 804 of temperature (in degrees C). Curve 806 represents the temperature of the inclination sensor 210 over time, while curve 808 represents angular measurements taken by the inclination sensor 210 over time. Graphs 700 and 800 shows that the prototype inclination sensor 210 provided accurate measurements during the testing over time and at the desired temperature range. [0047] Other testing on the prototype of the inclination sensor 210 was performed, including wireless communication testing, vibration testing, and shock testing. The wireless testing confirmed that a PCB on the inclination sensor 210 could communicate with a remote PCB so that stored angular measurements could be analyzed. The vibration testing and shock testing confirmed that a housing for the inclination sensor 210 could withstand the environment of the wellbore during milling operations. The vibration testing environment includes 30 g random profile at 2Hz to 1 kHz, in all three directions, as well as 30 g with 2 kHz sine wave in all three directions. The shock testing environment included 500 g at 1 ms and 2 ms durations.

[0048] Field testing of the inclination sensor 210 included operation of the sensor 210 on a BHA to test angular measurements at depth as shown in graph 900 of FIG. 9. Graph 900 shows angular measurements taken by a measurement- while-drilling (MWD) tool and the inclination sensor 210. Graph 900 includes x-axis 802 of wellbore depth (in feet) and y-axis 804 of angular measurements between a vertical wellbore and a lateral (or angled wellbore) (in degrees). Curve 906 represents the measurements from an MWD survey, while curve 908 represents measurements from the inclination sensor prototype. As shown in graph 900, the window of the lateral wellbore is at about 5300 feet, and a comparison of sensor readings and the MWD survey confirms the accurate measurement of the angle difference before and after the window by the prototype inclination sensor.

[0049] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, example operations, methods, or processes described herein may include more steps or fewer steps than those described. Further, the steps in such example operations, methods, or processes may be performed in different successions than that described or illustrated in the figures. Accordingly, other implementations are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A downhole tool, comprising: a milling assembly configured to couple to a tubular string and run into a vertical wellbore formed from a terranean surface to one or more subterranean formations, the milling assembly comprising: a tubular mandrel; a first mill coupled to the tubular mandrel at a downhole end of the tubular mandrel; and a second mill coupled to the tubular mandrel uphole of the first mill; and an inclination sensor mounted in or to the tubular mandrel between the first mill and the second mill, the inclination sensor configured to determine an angle between a lateral wellbore formed by the milling assembly from a window in the vertical wellbore and the vertical wellbore.

2. The downhole tool of claim 1, wherein the inclination sensor is mounted within a pocket formed in a wall of the tubular mandrel.

3. The downhole tool of claim 2, comprising a cover plate coupled to the tubular mandrel over the pocket to enclose the inclination sensor.

4. The downhole tool of claim 3, comprising one or more fasteners configured to couple at least one of the inclination sensor or the cover plate to the tubular mandrel.

5. The downhole tool of claim 1, wherein the inclination sensor is configured to determine: a first angle between the lateral w ellbore formed by the milling assembly from the window in the vertical wellbore and the vertical wellbore; and a second angle between the lateral wellbore formed by the milling assembly from the window- in the vertical wellbore and the vertical wellbore.

6. The downhole tool of claim 1, wherein the inclination sensor comprises a printed circuit board that comprises: at least one accelerometer; and at least one memory module communicably coupled to the at least one accelerometer.

7. The downhole tool of claim 1, comprising a third mill coupled to the tubular mandrel uphole of the second mill.

8. A drilling system, comprising: a whipstock configured couple to a casing positioned in a vertical wellbore formed from a terranean surface to one or more subterranean formations; and a bottom hole assembly comprising a milling assembly configured to couple to a tubular string and run into the vertical wellbore through the casing, the milling assembly comprising: a tubular mandrel; a plurality of mills, each mill coupled to the tubular mandrel; and an inclination sensor mounted in or to the tubular mandrel between two of the plurality of mills, the inclination sensor configured to determine an angle between a lateral wellbore formed by the milling assembly from a window in the vertical wellbore and the vertical wellbore.

9. The drilling system of claim 8, wherein the inclination sensor is mounted within a pocket formed in a wall of the tubular mandrel.

10. The drilling system of claim 9, comprising a cover plate coupled to the tubular mandrel over the pocket to enclose the inclination sensor.

11. The drilling system of claim 10, comprising one or more fasteners configured to couple at least one of the inclination sensor or the cover plate to the tubular mandrel.

12. The drilling system of claim 8, wherein the inclination sensor is configured to determine: a first angle between the lateral wellbore formed by the milling assembly from the window in the vertical wellbore and the vertical wellbore; and a second angle between the lateral wellbore formed by the milling assembly from the window in the vertical wellbore and the vertical wellbore.

13. The drilling system of claim 8, wherein the inclination sensor comprises a printed circuit board that comprises: at least one accelerometer; and at least one memory module communicably coupled to the at least one accelerometer.

14. The drilling system of claim 8, wherein the plurality of mills comprise a first mill positioned at a distal end of the tubular mandrel and a second mill positioned uphole of the first mill, and the inclination sensor is mounted in or to the tubular mandrel between the first and second mills.

15. A drilling method, comprising: running a downhole tool into a vertical w ellbore formed from a terranean surface to one or more subterranean formations, the downhole tool comprising a milling assembly that comprises: a tubular mandrel; a first mill coupled to the tubular mandrel at a downhole end of the tubular mandrel; a second mill coupled to the tubular mandrel uphole of the first mill; and an inclination sensor mounted in or to the tubular mandrel between the first mill and the second mill; urging the milling assembly through a window in a casing of the vertical wellbore with a whipstock positioned in the vertical wellbore; milling at least a portion of a lateral wellbore from the window; and during the milling, determining an angle between the lateral wellbore and the vertical w ellbore with the inclination sensor.

16. The drilling method of claim 15, w herein milling the portion of the lateral wellbore from the window comprises milling the portion of the lateral w ellbore with the first and second mills.

17. The drilling method of claim 15, comprising installing the inclination sensor within a pocket formed in a w all of the tubular mandrel.

18. The drilling method of claim 17, comprising securing the inclination sensor on or to the tubular mandrel with one or more tension bolts.

19. The drilling method of claim 15, wherein determining the angle between the lateral wellbore and the vertical wellbore with the inclination sensor comprises: determining a first angle between the lateral wellbore and the vertical wellbore; and determining a second angle between the lateral wellbore and the vertical wellbore.

20. The drilling method of claim 15, wherein determining the angle between the lateral wellbore and the vertical wellbore with the inclination sensor comprises determining the angle with at least one accelerometer.

21. The drilling method of claim 20, comprising: storing the determined angle in at least one memory module communicably coupled to the at least one accelerometer; and subsequent to running the milling assembly out of the vertical wellbore to the terranean surface, accessing the stored determined angle from the at least one memory module.