Drilling systems for geosteering with historical data and associated methods and devices

Abstract

A method of drilling a wellbore includes collecting historical data from a formation. The method further includes defining a stratigraphic signature of a region of interest in the historical data. The method also includes identifying boundary conditions of the region of interest. The method further includes capturing a real-time measurement from a downhole tool. The method also includes comparing the real-time measurement to the historical data. The method further includes determining a probability of the real-time measurement from the downhole tool being vertically positioned in the region of interest.

Description

[0001] DRILLING SYSTEMS FOR GEOSTEERING WITH HISTORICAL DATA AND ASSOCIATED METHODS AND DEVICES

[0002] PRIORITY CLAIM

[0003] This application claims the benefit of the filing date of United States Provisional Patent Application Serial No. 63 / 736,351. filed December 19, 2024, for “PROBABILISTIC BAYESIAN METHODS OF POST LANDING USING DISTRIBUTION TESTS AND TRUE STRATIGRAPHIC SIGNATURE FOR REAL-TIME WELL PLACEMENT,” the disclosure of which is hereby incorporated herein in its entirety by this reference.

[0004] TECHNICAL FIELD

[0005] Embodiments of the present disclosure generally relate to earth-boring operations. In particular, embodiments of the present disclosure relate to drilling systems for geosteering with historical data associated methods and devices.

[0006] BACKGROUND

[0007] Wellbore drilling operations may involve the use of an earth-boring tool at the end of a long string of pipe commonly referred to as a drill string. An earth-boring tool may be used for drilling through formations, such as rock, dirt. sand, tar, etc. In some cases, the earth-boring tool may be configured to drill through additional elements that may be present in a wellbore, such as cement, casings (e.g., a wellbore casing), discarded or lost equipment (e.g., fish, junk, etc.), packers, etc. In some cases, earth-boring tools may be configured to drill through plugs (e.g.. fracturing plugs, bridge plugs, cement plugs, etc.). In some cases, the plugs may include slips or other types of anchors, and the earth-boring tool may be configured to drill through the plug and any slip, anchor, and other component thereof.

[0008] A drill string operator may interpret information transmitted from downhole to make operational decisions, such as making adjustments to operating parameters, tripping the drill string out to inspect and / or replace components of the drill string, etc. Logging while drilling (LWD) tools send back data about the formation being drilled in real time. The operator may use the real-time data to guide the direction of a well, so it stays in the best part of the oil or gas reservoir. BRIEF SUMMARY

[0009] Embodiments of the disclosure include a method of drilling a wellbore. The method includes collecting historical data from a formation. The method further includes defining a stratigraphic signature of a region of interest in the historical data. The method also includes identifying boundary7conditions of the region of interest. The method further includes capturing a real-time measurement from a downhole tool. The method also includes comparing the real-time measurement to the historical data. The method further includes determining a probability of the real-time measurement from the downhole tool being vertically positioned in the region of interest.

[0010] Other embodiments of the disclosure include a drilling system. The drilling system includes a downhole measuring device. The drilling system further includes a memory device storing historical drilling data from a similar formation. The drilling system also includes a display device. The drilling system further includes non-transitory computer readable medium storing instructions thereon that, when executed by at least one processor, cause the at least one processor to perform steps that include defining a stratigraphic signature of a region of interest in the historical drilling data. The steps further include receiving a realtime measurement from the downhole measuring device. The steps also include comparing the real-time measurement to the historical data. The steps further include determining a relative vertical location of the downhole measuring device on the stratigraphic signature of the region of interest. The steps also include displaying a steering recommendation on the display device based on the relative vertical location of the downhole measuring device.

[0011] Another embodiment of the disclosure includes a method of drilling a wellbore. The method includes defining a stratigraphic signature of a formation based on historical data. The method further includes receiving real-time data from a downhole tool. The method also includes synchronizing the real-time data to the stratigraphic signature. The method further includes receiving a real-time measurement from the downhole tool. The method also includes determining a probability of the real-time measurement from the downhole tool being vertically positioned in a region of interest of the stratigraphic signature. The method further includes steering the downhole tool vertically if the probability of the real-time measurement being vertically positioned in the region of interest is determined to be low-. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] While the specification concludes with claims particularly pointing out and distinctly claiming embodiments of the present disclosure, the advantages of embodiments of the disclosure may be more readily ascertained from the following description of embodiments of the disclosure when read in conjunction with the accompanying drawings in which:

[0013] FIG. 1 illustrates an earth-boring system in accordance with an embodiment of the present disclosure;

[0014] FIG. 2 illustrates schematic view of a wellbore in a formation in accordance with embodiments of the disclosure;

[0015] FIG. 3 illustrates a data log plot of a w ellbore in accordance with embodiments of the disclosure;

[0016] FIG. 4 illustrates a comparison between data logs of two offset wellbores in accordance with embodiments of the disclosure;

[0017] FIG. 5 illustrates a schematic view7of a w ellbore vertically aligned with a data log from an offset wellbore in accordance with embodiments of the disclosure;

[0018] FIG. 6 illustrates a plot of statistical trendlines associated with a data log of a wellbore in accordance with embodiments of the disclosure; and

[0019] FIG. 7 illustrates a method of geosteering a drilling system in accordance with embodiments of the disclosure.

[0020] DETAILED DESCRIPTION

[0021] The illustrations presented herein are not meant to be actual views of any particular earth-boring system or component thereof, but are merely idealized representations employed to describe illustrative embodiments. The drawings are not necessarily to scale.

[0022] As used herein, the terms ‘'earth-boring tool” means and includes any type of bit or tool used for drilling during the formation or enlargement of a wellbore in a subterranean formation. For example, earth-boring tools include fixed-cutter bits, roller cone bits, percussion bits, core bits, eccentric bits, bicenter bits, reamers, mills, drag bits, hybrid bits (e.g.. rolling components in combination with fixed cutting elements), and other drilling bits and tools known in the art.

[0023] As used herein, the term “substantially” in reference to a given parameter, property7, or condition means and includes to a degree that one of ordinary skill in the art would understand that the given parameter, property, or condition is met with a degree of variance, such as within acceptable tolerances. By way of example, depending on the particular parameter, property, or condition that is substantially met, the parameter, property, or condition may be at least 90.0 percent met, at least 95.0 percent met, at least 99.0 percent met, at least 99.9 percent met, or even 100.0 percent met.

[0024] As used herein, “about” or “approximately” in reference to a numerical value for a particular parameter is inclusive of the numerical value and a degree of variance from the numerical value that one of ordinary skill in the art would understand is within acceptable tolerances for the particular parameter. For example, “about” or “approximately” in reference to a numerical value may include additional numerical values within a range of from 90.0 percent to 110.0 percent of the numerical value, such as within a range of from 95.0 percent to 105.0 percent of the numerical value, within a range of from 97.5 percent to 102.5 percent of the numerical value, within a range of from 99.0 percent to 101.0 percent of the numerical value, within a range of from 99.5 percent to 100.5 percent of the numerical value, or within a range of from 99.9 percent to 100. 1 percent of the numerical value.

[0025] As used herein, relational terms, such as “first,” “second,” “top,” “bottom,” etc., are generally used for clarity and convenience in understanding the disclosure and accompanying drawings and do not connote or depend on any specific preference, orientation, or order, except where the context clearly indicates otherwise.

[0026] As used herein, the term “and / or” means and includes any and all combinations of one or more of the associated listed items.

[0027] As used herein relative directional terms, such as “ahead” or “behind” refer to a direction of travel of a component of the drill string. For example, undrilled formation may be positioned ahead of an earth-boring tool and a drilling platform (e.g., the surface) may be positioned behind the earth-boring tool.

[0028] As used herein, the terms “longitudinal,” “vertical,” “lateral,” and “horizontal” are in reference to a major plane of a substrate (e.g., base material, base structure, base construction, etc.) in or on which one or more structures and / or features are formed and are not necessarily defined by Earth’s gravitational field. A “lateral” or “horizontal” direction is a direction that is substantially parallel to the major plane of the substrate, while a “longitudinal” or “vertical” direction is a direction that is substantially perpendicular to the major plane of the substrate. The major plane of the substrate is defined by a surface of the substrate having a relatively large area compared to other surfaces of the substrate. With reference to the figures, a “horizontal” or “lateral” direction may be perpendicular to an indicated “Z” axis, and may be parallel to an indicated “X” axis and / or parallel to an indicated “Y” axis; and a “vertical” or “longitudinal” direction may be parallel to an indicated “Z” axis, may be perpendicular to an indicated “X” axis, and may be perpendicular to an indicated “Y” axis.

[0029] When drilling a wellbore, operating decisions, such as steering decisions, drilling speed decisions, weight on bit decisions, etc., are made at the surface based on data transmitted from the drilling equipment disposed in the wellbore. Maintaining the end of the drilling equipment in a desired region of the formation may result in an increase in productivity of the well. However, the regions in a formation are not uniform. Therefore, after entering the desired region and while proceeding forward in a lateral well, further adjustment to the drilling direction may be needed to maintain the end of the drilling equipment within the desired region. Embodiments of the disclosure may facilitate using historical data to detect region boundaries to improve the ability of an operator to detect the approach of a regional boundary and take corrective action.

[0030] FIG. 1 illustrates an earth-boring system 100. An earth-boring system 100 may include a drill string 102. The drill string 102 may include multiple sections of drill pipe coupled together to form a long string of drill pipe. A forward end of the drill string 1 2 may include a bottom hole assembly 104 (BHA). The BHA 104 may include components, such as a motor 106 (e.g., mud motor), one or more reamers 108 and / or stabilizers 110, and an earth-boring tool 112, such as a drill bit. The BHA 104 may also include electronics, such as sensors 114, modules 116. and / or tool control components 118. The drill string 102 may be inserted into a borehole 120. The borehole 120 may be formed by the earth-boring tool 112 as the drill string 102 proceeds through a formation 122. The tool control components 118 may be configured to control an operational aspect of the earth-boring tool 112. For example, the tool control components 118 may include a steering component configured to change an angle of the earth-boring tool 112 with respect to the drill string 102 changing a direction of advancement of the drill string 102. The tool control components 118 may be configured to receive instructions from an operator at the surface and perform actions based on the instructions. In some embodiments, control instructions may be derived downhole within the tool control components 118, such as in a closed loop system, etc.

[0031] The sensors 1 14 may be configured to collect information regarding the downhole conditions such as temperature, pressure, vibration, fluid density, fluid viscosity, cutting density, cutting size, cutting concentration, etc. In some embodiments, the sensors 114 may be configured to collect information regarding the formation, such as formation composition, formation density, etc. In some embodiments, the sensors 114 may be configured to collect information regarding the earth-boring tool 112, such as tool temperature, cutter temperature, cutter wear, weight on bit (WOB), torque on bit (TOB), string rotational speed (RPM), drilling fluid pressure at the earth-boring tool 112, fluid flow rate at the earth-boring tool 112, etc.

[0032] The information collected by the sensors 114 may be processed, stored, and / or transmitted by the modules 116. For example, the modules 116 may receive the information from the sensors 1 14 in the form of raw data, such as a voltage (e.g., 0-10 VDC, 0-5 VDC, etc.), an amperage (e.g., 0-20 mA, 4-20 mA, etc.), or a resistance (e.g., resistance temperature detector (RTD), thermistor, etc.). The module 116 may process raw sensor data and transmit the data to the surface on a communication network, using a communication network protocol to transmit the raw sensor data. The communication network may include, for example, a communication line, mud pulse telemetry, electromagnetic telemetry, wired pipe, etc. In some embodiments, the modules 116 may be configured to run calculations with the raw sensor data, for example, calculating a viscosity of the drilling fluid using the sensor measurements such as temperatures, pressures, or calculating a rate of penetration of the earth-boring tool 112 using sensor measurements such as cutting concentration, cutting density, WOB, formation density, etc.

[0033] In some embodiments, the downhole information may be transmitted to a control center 126 on a platform 124 at the surface or to a remote computing device at the surface. For example, the downhole information may be provided to the operator through a display, a printout, etc., in the control center 126, or at the remote computing device. In some embodiments, the downhole information may be transmitted to a computing device that may process the information and provide the information to the operator in different formats useful to the operator. For example, measurements that are out of range may be provided in the form of alerts, warning lights, alarms, etc., some information may be provided live in the form of a display, spreadsheet, etc., whereas other information that may not be useful until further calculations are performed may be processed and the result of the calculation may be provided in the display, print out, spreadsheet, etc.

[0034] FIG. 2 illustrates a schematic view of a formation 200 and a wellbore path 202 through the formation 200. The formation 200 includes multiple stratigraphic sections 204. The stratigraphic sections 204 may be formed from different types of material, such as mud, sand, gravel, silt, clay, sedimentary rock (e.g., sandstone, shale, limestone, conglomerate, etc ), igneous rock (e.g., granite, basalt, diorite, etc.), metamorphic rock (e.g., schist, gneiss, slate, etc.). The stratigraphic sections 204 may be arranged in a vertical stack throughout the formation 200, such that two neighboring stratigraphic sections 204 of different materials define a boundary 206 between the two neighboring stratigraphic sections 204.

[0035] The stratigraphic sections 204 may have different thicknesses (e.g., vertical thicknesses in the Z-direction or stratigraphic thicknesses in the Z-direction). Furthermore, any one stratigraphic section 204 may have a different vertical thickness at different lateral locations (e g., in the X direction or Y direction). Thus, the boundary 206 between two neighboring stratigraphic sections 204 in a first lateral position may be in a different vertical position from the boundary 206 between the same two neighboring stratigraphic sections 204 in a second different lateral position.

[0036] One or more of the stratigraphic sections 204 may be a desired region 208 (e.g., a region of interest). For example, the desired region 208 may include a reservoir of a desirable material, such as oil, natural gas, water, etc. For example, the desired region 208 may be formed from a porous material, such as a sedimentary’ rock, sand, gravel, etc. As illustrated in FIG. 2. the desired region 208 lies vertically beneath multiple other stratigraphic sections 204. Therefore, the wellbore path 202 passes through the multiple other stratigraphic sections 204 before reaching the desired region 208. The region of the wellbore path 202 before reaching the desired region 208 is referred to herein as the pre-landing region 210. The wellbore path 202 within the pre-landing region 210 is substantially vertical. Upon reaching the desired region 208, the wellbore path 202 may turn to run in a substantially horizonal direction (e.g., substantially parallel with the X-axis or Y-axis), such that the wellbore path 202 extends a greater distance into the desired region 208. The region of the wellbore path 202 after the wellbore path 202 turns into the desired region 208 is referred to herein as the post-landing region 212. In the post-landing region 212, geosteering may be used to steer the wellbore toward the stratigraphic section 204 associated with the desired region 208. Geosteering is a drilling technique that uses real-time data to steer or adjust the wellbore trajectory toward the desired region 208, such as to maximize production of the wellbore. In other words, it involves attempting to steer the drill bit to the most productive region of a formation using real-time geological information. Embodiments of the disclosure use a comparison between real-time data and historical data taken from offset wellbores in the same formation to make geosteering decisions. FIG. 3 illustrates a data log 300 of a wellbore path (e.g., the wellbore path 202 (FIG. 2)) through a formation (e.g.. the formation 200 (FIG. 2)). The data log 300 shows formation values 302 at different depths 304. The formation values 302 may be direct readings from a logging while drilling (LWD) tool, such as a gamma ray tool, spectral gamma ray tool, sonar tool, neutron porosity' tool, resistivity' tools, etc. Therefore, the formation values 302 may be gamma ray measurements, resistivity measurements, acoustic measurements, neutron porosity measurements, etc.

[0037] The depth 304 of each formation value 302 is a measurement of a length of the wellbore path where the formation value 302 was measured (e.g., a distance from the surface along the wellbore path). Therefore, the depth 304 may be different from a vertical depth (e.g.. in the Z-direction) from the surface. For example, in a pre-landing region of the wellbore path, the depth 304 may be similar to the stratigraphic depth, as the wellbore path is a substantially^ vertical path. In the post-landing region of the wellbore path, the depth 304 may continue to increase while a vertical depth may remain substantially the same as the wellbore path extends in a substantially horizontal direction.

[0038] As illustrated in FIG. 3, the formation values 302 form an undulating log of values that varies at different depths 304. There are multiple distinct changes in the undulating log of the formation values 302 that indicate a boundary' 308 between two different types of material in the associated formation, such as boundaries 308 (e.g., boundaries 206 (FIG. 2)) between stratigraphic sections 312a. 312b, 312c, 312d, 312e (e.g., stratigraphic sections 204 (FIG. 2)) of the associated formation. For example, the undulating formation values 302 may change, such that a trendline 310 (e.g., regression line, median line, etc.) of the undulating formation values 302 abruptly increases or decreases relative to the trendline 310 of the undulating formation values 302 at a neighboring depth. In another example, a boundary 308 may be identified where a pattern or path defined by the trendline 310 of the undulating formation values 302 abruptly changes, forming a sharp comer or point. In some embodiments, the trendline 310 is a line that is statistically fit to the formation values 302 (e.g., the raw data), such as through a regression analysis (e.g., linear regression, nonlinear regression, least squares regression, etc.).

[0039] The formation values 302 between the identified boundaries 308 may exhibit a stratigraphic signature 306. The stratigraphic signature 306 may include a pattern in the undulating formation values 302 or a pattern or path of the trendline 310 of the undulating formation values 302, such as a curve or substantially straight line. In some embodiments, the stratigraphic signature 306 may be different in a central region of the associated stratigraphic section 312a. 312b, 312c, 312d, 312e than the stratigraphic signature 306 in a region nearing the associated boundaries 308. In some embodiments, the stratigraphic signature 306 is used to determine the type of material present in the associated stratigraphic section 312a, 312b, 312c, 312d, 312e. In other embodiments, the stratigraphic signature 306 is used to determine which stratigraphic section 312a, 312b, 312c, 312d. 312e the measurement is taken from, such as through a comparison with historical data.

[0040] In the data log 300 illustrated in FIG. 3, the trendline 310 of the formation values 302 in a first stratigraphic section 312a exhibits an increasing slope as the depth 304 increases. At the boundary 308 between the first stratigraphic section 312a and the second stratigraphic section 312b, the trendline 310 abruptly decreases before following an S-shaped curved path, further decreasing to a steady value extending in a substantially straight line (e.g., substantially constant formation value 302) through the remaining depths 304 associated with the second stratigraphic section 312b. At the boundary' 308 between the second stratigraphic section 312b and the third stratigraphic section 312c, the trendline 310 abruptly changes from the substantially straight line of the second stratigraphic section 312b to a curve having a Bezier curve or parabolic curve shape in the third stratigraphic section 312c. At the boundary 308 between the third stratigraphic section 312c and the fourth stratigraphic section 312d, the trendline 310 abruptly increases from the relatively lower formation values 302 at the end of the curve of the third stratigraphic section 312c to relatively larger formation values 302 in the fourth stratigraphic section 312d. The trendline 310 follows an S-shaped curved path through the fourth stratigraphic section 312d gradually decreasing in formation values 302 as the depth 304 increases until reaching the boundary 308 between the fourth stratigraphic section 312d and the fifth stratigraphic section 312e. At the boundary 308 between the fourth stratigraphic section 312d and the fifth stratigraphic section 312e, the trendline 310 abruptly increases from the relatively low formation value 302 of the fourth stratigraphic section 312d to a relatively large formation value 302 of the fifth stratigraphic section 312e. The trendline 310 then follows a substantially linear path with a decreasing slope as the depth 304 continues to increase through the fifth stratigraphic section 312e.

[0041] The shapes of the trendline 310 in each stratigraphic section 312a, 312b, 312c, 312d, 312e may define the stratigraphic signature 306 of each respective stratigraphic section 312a, 312b, 312c, 312d, 312e. The abrupt changes in the trendline 310 at the boundaries 308 may similarly define signature changes between the respective stratigraphic sections 312a, 312b, 312c, 312d, 312e. These signatures may be used to compare the data log 300 to other data logs from other wellbores (e.g., offset wellbores) in a same formation or a similar formation.

[0042] FIG. 4 illustrates a comparison between the data log 300 and a data log 400 from an offset wellbore in the same formation. The formation values 402 logged in the data log 400 are the same types of measurements as the formation values 302 of the data log 300, and the data log 300 and the data log 400 are aligned such that the depths 304 of the data log 300 are the same as the laterally aligned depths 404 of the data log 400 (e g., a horizontal line rawn across both the data log 300 and the data log 400 passes through the same value for the depths 304, 404 of the respective data logs 300, 400).

[0043] The formation values 402 of the data log 400 define trendlines 410 that define stratigraphic signatures 406 of the stratigraphic sections 412a, 412b, 412c, 412d, 412e of the formation. Abrupt changes to the trendlines 410 are used to identify boundaries 408 betw een the stratigraphic sections 412a, 412b, 412c, 412d, 412e. As illustrated in FIG. 4, the boundaries 408 of the data log 400 occur at different depths 404 than the boundaries 308 of the data log 300. As discussed above, stratigraphic sections within a formation may have varying thicknesses at different lateral positions in the formation. Therefore, the depths of the boundaries between the stratigraphic sections within the formation will also vary at different lateral positions within the formation.

[0044] As illustrated in FIG. 4, the stratigraphic signatures 406 of the formation values 402 in the data log 400 have similar shapes to the stratigraphic signatures 306 of the formation values 302 in the data log 300. The signature changes between stratigraphic sections 412a, 412b, 412c, 412d, 412e at the respective boundaries 408 are also similar in shape and type when compared to the signature changes between the stratigraphic sections 312a, 312b, 312c, 312d, 312e of the data log 300. These similarities are used to correlate the stratigraphic sections 412a, 412b, 412c, 412d, 412e of the data log 400 to the respective stratigraphic sections 312a, 312b, 312c, 312d, 312e of the data log 300. This correlation may facilitate the use of historical data from the w ellbore associated with the data log 300 for analyzing realtime data from the wellbore associated with the data log 400. For example, a desired region of the stratigraphic sections 412a, 412b, 412c, 412d, 412e may be identified based on which of the stratigraphic sections 312a, 312b, 312c, 312d, 312e w as the desired region in the prior w ellbore. Furthermore, as discussed in further detail below, these correlations may facilitate determining if the BHA has left the desired region when drilling laterally (e.g., in the post- landing region of the wellbore) and whether the desired region is above or below the BHA to aid the operator in making steering decisions.

[0045] FIG. 5 illustrates a schematic view of a formation 500 including a wellbore path 502 passing therethrough. FIG. 5 also includes an offset wellbore log 504 (e.g., the data log 300 or data log 400). The offset wellbore log 504 includes a trendline 506. As discussed above, the trendline 506 defines stratigraphic signatures and boundary signatures that can be used to identify the stratigraphic sections and boundaries between the stratigraphic sections in the associated wellbore. As discussed above, a trendline of the formation values measured by an LWD tool in the wellbore path 502 will define similar stratigraphic signatures and boundary signatures that can be used to identify stratigraphic sections 508 in the formation 500 and boundaries 510 between the stratigraphic sections 508 in the formation 500.

[0046] A comparison between the trendline 506 of the offset wellbore log 504 and the trendline in the real-time data being gathered by the LWD tool in the wellbore path 502 may facilitate determining where the LWD tool is located within the formation at any given time. When comparing the trendline 506 of the offset wellbore log 504 to the trendline in the realtime data being gathered by the LWD tool in the wellbore path 502. the trendline in the realtime data is first synchronized with the trendline 506 of the offset wellbore log 504. As discussed above, the stratigraphic signature shapes and stratigraphic signature changes defined by the trendline in the real-time data may occur at different depths from the similar stratigraphic signature shapes and stratigraphic signature changes in the trendline 506. Therefore, to synchronize the real-time data to the offset wellbore log 504, the similar stratigraphic signature shapes and stratigraphic signature changes may be identified to determine which of the stratigraphic sections 508 the LWD tool is in. Determining which of the stratigraphic sections 508 the LWD tool is in may facilitate determining when to begin turning the BHA into a horizontal path to enter a desired region 512 of the stratigraphic sections 508, such as a stratigraphic section 508 including a reservoir of desired materials.

[0047] In some embodiments, the initial synchronization is accomplished during a prelanding region 514 of the wellbore path 502 as the wellbore path 502 extends substantially vertically through multiple stratigraphic sections 508 and boundaries 510. In other embodiments, the synchronization is accomplished when the wellbore path 502 passes from a first stratigraphic section 508 to a second stratigraphic section 508 through a boundary 510, where the stratigraphic signatures of the first and second stratigraphic sections 508 and the stratigraphic signature change across the boundary 510 are sufficiently unique to identify which portion of the offset wellbore log 504 corresponds to the first and second stratigraphic sections 508.

[0048] After the trendline in the real-time data is synchronized with the trendline 506 of the offset wellbore log 504, the location of the LWD within a specific stratigraphic section 508 may be estimated by comparing the stratigraphic signatures defined by the trendline 506 of the offset wellbore log 504 to changes in the real-time data. The estimations of the location of the LWD within a specific stratigraphic section 508 may facilitate greater accuracy when drilling horizontally in a post-landing region 516 of the wellbore path 502. For example, in the embodiment illustrated in FIG. 5, a first point 518 in the wellbore path 502 is shown with a correlated first point 518 on the trendline 506 of the offset wellbore log 504. Similarly, a second point 520 in the wellbore path 502 is shown with a correlated second point 520 on the trendline 506 of the offset wellbore log 504. A third point 522 in the wellbore path 502 is also show n with a correlated third point 522 on the trendline 506 of the offset wellbore log 504.

[0049] As illustrated in FIG. 5, the second point 520 is vertically higher in the stratigraphic section 508 than the first point 518. As discussed above, the depth in the offset wellbore log 504 is measured as a distance along the associated wellbore rather than a vertical depth. However, while the second point 520 is a greater distance along the wellbore path 502 than the first point 518, the second point 520 may be correlated to a point in the offset wellbore log 504 that occurred earlier in the associated wellbore than the point correlated with the first point 518, because once the real-time data of the wellbore path 502 is synchronized with the offset wellbore log 504, the stratigraphic signature defined by the trendline 506 of the offset w ellbore log 504 may be used to estimate a true vertical depth or a true stratigraphic depth (e.g., in the Z-direction) within the associated stratigraphic section 508 rather than a depth along the associated wellbore path 502.

[0050] Estimating a true vertical depth of the LWD tool within the associated stratigraphic section 508 may facilitate determining if the LWD tool is vertically or stratigraphically close to a boundary 510 of the stratigraphic section 508. If the stratigraphic section 508 is the desired region 512, an operator may make a steering decision to facilitate maintaining the LWD tool within the desired region 512 when the real-time data comparison with the stratigraphic signature indicates that the LWD tool is vertically or stratigraphically close to a boundary' 510. Stratigraphic signature changes may also provide an indication that the LWD tool has crossed a boundary. For example, in the embodiment illustrated in FIG. 5, the third point 522 is positioned in a stratigraphic section 508 that is below the desired region 512. A comparison of the trendline associated with the real-time data of the wellbore path 502 and the trendline 506 of the offset wellbore log 504 may identify a stratigraphic signature change that defines the boundary 510 between the stratigraphic section 508 of the desired region 512 and the neighboring stratigraphic section 508. Furthermore, the comparison may identify that the stratigraphic signature change is vertically below the stratigraphic section 508 of the desired region 512. Therefore, the comparison may indicate that the LWD tool in the wellbore path 502 has a true vertical depth that passed below the stratigraphic section 508 of the desired region 512. With this information, an operator may then steer the BHA vertically upward to reenter the stratigraphic section 508 of the desired region 512.

[0051] FIG. 6 illustrates a plot 600 of trendlines associated with a data log (e.g., data log 300, data log 400, offset wellbore log 504, etc.). The plot 600 includes formation values 604 on a first axis and depths 606 on a second axis. The depths 606 on the plot 600 may be converted to true vertical depths or true stratigraphic depths. For example, the data used for the plot may only be taken from pre-landing region of the offset wellbore, such that the data substantially coincides with a vertical depth or stratigraphic depth within a formation instead of a length of the associated wellbore.

[0052] In some embodiments, the data log used in the plot 600 may be collectively gathered data from multiple offset wellbores in the same formation. In other embodiments, the 600 is formed using data from a single data log from a single offset wellbore. After the data has been compiled, multiple different trendlines 608a, 608b, 608c, 608d, 608e may be fit to the data. In FIG. 6, the plot 600 includes a minimum trendline 608a, a maximum trendline 608e, a pl 0 trendline 608b, a median trendline 608c. and ap90 trendline 608d. As discussed above, the data logs may have undulating values. Thus, the values from each data log define a range of formation values 604 at each depth 606. The minimum trendline 608a is fit to the smallest formation values 604 at each depth 606 and the maximum trendline 608e is fit to the largest formation values 604 at each depth 606. The plO trendline 608b is fit to the 10th percentile formation values 604 at each depth 606; the median trendline 608c is fit to the median formation values 604 at each depth; and the p90 trendline 608d is fit to the 90th percentile formation values 604 at each depth 606.

[0053] As discussed above, the median trendline 608c may be used for a comparison with the measured or real-time values of a target wellbore. FIG. 6 illustrates an example of how a target wellbore value would be compared to the historical data 602 plotted on the plot 600. In the example illustrated on the plot 600, a target measurement 610 of 40 is measured at a depth 606 of 5100. Using the real-time target measurement 610 and target depth 612, a probability of the target wellbore being within the same stratigraphic section as the historical data 602 is calculated. First, the median value of the historical data 602 at the target depth 612 is found using the median trendline 608c. Then, a first range 614 of depths 606 where the formation values 604 of the historical data 602 exceed the median value around the target depth 612 is found. Second, a second range 616 of depths 606 where the formation values 604 of the historical data 602 are less than the target measurement 610 around the target depth 612 is found. After the first range 614 and the second range 616 are found, a statistical evaluation, such as the Kolmogorov-Smirnoff test, is used to find a probability (e.g., P value) of the target measurement 610 falling within the historical data 602 at the target depth 612.

[0054] A high value for the probability may indicate that the target wellbore is likely to be in a same stratigraphic section as the historical data 602 that is associated with the target depth 612, whereas a low value for the probability may indicate that the target wellbore is likely to be outside the stratigraphic section of the historical data 602 that is associated with the target depth 612. If the target measurement 610 is found to be outside the desired stratigraphic section of the historical data 602, the probability calculations may be used on prior data from the target wellbore to determine which direction the target wellbore is likely to have left the desired stratigraphic section, which may assist the operator in making a subsequent steering decision.

[0055] FIG. 7 illustrates a flow chart representative of a method 700 of geosteering a drilling system to form a wellbore. As discussed above, these methods may be used to make steering decisions to maintain the BHA within a desired region of the associated formation.

[0056] Data from the formation is collected as historical data in act 702. As discussed above, the historical data may be data logs from other wellbores (e.g., offset wellbores) drilled in the same formation. The historical data may be the data long from a single offset wellbore or the combined data logs from multiple offset wellbores. The historical data may be the raw formation data collected from an LWD tool, such as a gamma ray tool, spectral gamma ray tool, sonar tool, neutron porosity tool, resistivity tools, etc. Therefore, the formation data may be gamma ray measurements, resistivity measurements, acoustic measurements, neutron porosity measurements, etc. Statistical trendlines may be fit to the historical data, such as minimum trendlines, maximum trendlines, and median trendlines. The statistical trendlines may be used to define stratigraphic signatures of the different stratigraphic sections of the formation in act 704. A desired region, such as a region including a desirable material or mineral, is then identified within the stratigraphic signatures. For example, the stratigraphic section including the desired region may be identified. Then the stratigraphic signature of the stratigraphic section including the desired region is identified as the stratigraphic signature of the desired region.

[0057] As discussed above, the stratigraphic signatures are also used to identify boundaries between the stratigraphic sections. Therefore, the boundary conditions of the stratigraphic section including the desired region can be identified in act 706. The boundary conditions may include gradual changes in the historical formation values as they approach the boundary and / or more dramatic or abrupt changes in the historical formation values after the boundary7is crossed. In some stratigraphic signatures, the changes in the formation values may be larger as a boundary approaches. In other stratigraphic signatures, the formation values my remain substantially constant until the boundary is crossed.

[0058] While drilling a target wellbore, an LWD tool may be used to capture real-time measurements in act 708. The LWD tool is the same type of tool as the LWD tool(s) used to capture the historical data, such that the measurement captured in real-time are the same ty pes of measurements as the historical data. For example, if the historical data is a log of gamma ray measurements, the real-time measurements are also gamma ray measurements.

[0059] The captured real-time measurements are then compared with the historical data in act 710. As discussed above, the real-time measurements are first synchronized with the historical data. Synchronizing the real-time measurements with the historical data aligns the real-time measurements with historical data from similar stratigraphic sections. The realtime measurements may be synchronized with the historical data by identifying boundary conditions between stratigraphic signatures in the real-time data and aligning the boundary conditions with the boundary7conditions that have been identified in the historical data. As discussed above, different stratigraphic sections have different stratigraphic signatures and different stratigraphic signature changes across the boundaries. When aligning the boundary conditions of the real-time data and the historical data, the stratigraphic signatures and stratigraphic changes in each of the real-time data and the historical data are considered, such that the aligned boundaries and stratigraphic signatures are similar and can be considered to be measurements of the same stratigraphic section. Once the real-time measurements are synchronized with the historical data, a realtime measurement can be compared to the historical data to determine if the real-time measurement was captured from a point within the stratigraphic section including the desired region in act 712. The probability of the real-time measurement being within the desired stratigraphic section may be calculated in the manner discussed above, with respect to FIG. 6. The target depth may be determined based on the synchronization of the real-time measurements with the historical data, such that the target depth is determined to be in the stratigraphic section where the real-time measurement is estimated to be based on the synchronization. The target depth may then be used to determine the first range as discussed in greater detail above. The real-time measurement may then be used to determine the second range as discussed in greater detail above. The two ranges may then be used to determine the probability that the measured value lies within the stratigraphic section where the real-time measurement was estimated to be taken based on the synchronization.

[0060] If the probability value is high, such as in a range from about 30% to about 100%, from about 40% to about 100%, or from about 50% to about 100%, the BHA may be identified as being in the stratigraphic section where the real-time measurement was estimated to have been taken. If the probability value is low, such as in a range from about 0% to about 50%, from about 0% to about 40%, or from about 0% to about 30%, the BHA may be identified as being outside the stratigraphic section where the real-time measurement was estimated to have been taken. In some embodiments, where the probability value is in a midrange, such as from about 30% to about 70% or from about 40% to about 60%, further probability calculations based on earlier real-time measurements may be considered to determine if the probability of the BHA being at the estimated true vertical depth is increasing or decreasing.

[0061] If the probability values are low or in the mid-range, further considerations and / or calculations may be used to determine if the BHA is approaching or has crossed one of the boundaries of the stratigraphic section. For example, a similar probability calculation may be performed with the target depth set within the neighboring stratigraphic sections to determine if there is a greater probability that the measurement was taken from one of the neighboring stratigraphic sections. In some embodiments, a trend of the real-time measurements approaching the targe real-time measurement may be compared to the historical trendlines. The comparison of the trend of the real-time measurements and the historical trendlines may demonstrate where the target real-time measurements match up on the stratigraphic signatures and signature changes. Between the probabilities and the mating of the stratigraphic signatures and signature changes, it can be determined if the BHA is approaching or has crossed a boundary between stratigraphic sections and which boundary is being approached or has been crossed.

[0062] Once it has been determined that the BHA is approaching or has crossed a boundary and which boundary is being approached or has been crossed, a steering recommendation may be provided in act 714. In some embodiments, the steering recommendation is displayed on a graphical user interface for the operator. For example, a formation schematic may be displayed and an estimated real-time true vertical depth location of the BHA within the formation may be displayed, such that the operator may see if the BHA is approaching or has crossed a boundary of the desired stratigraphic section. In another example, a readout may be provided with a recommendation to steer the BHA in a specified direction (e.g., up or down) based on the probability calculations. In some embodiments, the historical trendline may be displayed and the real-time data may be overlaid with an alert when the probability of the real-time data being within the desired stratigraphic section is below a threshold value.

[0063] In some embodiments, the probability calculations and steering recommendations are performed by a processor on the drilling equipment, such as a processor on the drilling platform at the surface or a processor in a module in the drill string, such as in the BHA. In some embodiments, the processor prepares and displays the steering recommendation to the operator. In other embodiments, the processor may be configured to prepare and send commands to the BHA to control a steering device in the BHA and automatically steer the BHA based on the probability calculations and matching the stratigraphic signatures.

[0064] Non-limiting exemplary embodiments of the disclosure include:

[0065] Embodiment 1 : A method of drilling a wellbore, the method comprising: collecting historical data from a formation; defining a stratigraphic signature of a region of interest in the historical data; identifying boundary conditions of the region of interest; capturing a realtime measurement from a downhole tool; comparing the real-time measurement to the historical data; and determining a probability of the real-time measurement from the downhole tool being stratigraphically positioned in the region of interest.

[0066] Embodiment 2: The method of embodiment 1 , further comprising synchronizing the real-time measurement to the historical data before determining the probability of the realtime measurement from the downhole tool being stratigraphically positioned in the region of interest. Embodiment 3: The method of embodiment 2, wherein synchronizing the real-time measurement to the historical data comprises synchronizing a real-time stratigraphic signature to the stratigraphic signature.

[0067] Embodiment 4: The method of any one of embodiments 2 or 3, wherein synchronizing the real-time measurement to the historical data comprises converting a depth of the real-time measurement to a true vertical depth.

[0068] Embodiment 5: The method of any one of embodiments 1 through 4. wherein identifying the boundary conditions comprises identifying stratigraphic signature changes defining boundaries between stratigraphic sections of the formation.

[0069] Embodiment 6: The method of any one of embodiments 1 through 5, wherein defining the stratigraphic signature of the region of interest in the historical data comprises defining the stratigraphic signature with a trendline fit to the historical data.

[0070] Embodiment 7: The method of any one of embodiments 1 through 6, wherein collecting the historical data from the formation comprises converting depth measurements associated with the historical data to true vertical depths.

[0071] Embodiment 8: The method of any one of embodiments 1 through 7, further comprising: collecting real-time data including multiple real-time measurements; and fitting a trendline to the real-time data.

[0072] Embodiment 9: The method of embodiment 8. further comprising: comparing the trendline to the stratigraphic signature of the region of interest; and determining a relationship of the real-time measurement to the boundary conditions of the region of interest.

[0073] Embodiment 10: The method of embodiment 9, steering the downhole tool vertically toward the region of interest if the real-time measurement is determined to be proximate or across the boundary conditions of the region of interest.

[0074] Embodiment 11 : A drilling system comprising: a downhole measuring device; a memory device storing historical drilling data from a similar formation; a display device; and non-transitory computer readable medium storing instructions thereon that, when executed by at least one processor, cause the at least one processor to perform steps comprising: define a stratigraphic signature of a region of interest in the historical drilling data; receive a real-time measurement from the downhole measuring device; compare the real-time measurement to the historical data; determine a relative vertical location of the downhole measuring device on the stratigraphic signature of the region of interest; and display a steering recommendation on the display device based on the relative vertical location of the downhole measuring device.

[0075] Embodiment 12: The drilling system of embodiment 11, wherein the instructions cause the at least one processor to: receive real-time data including multiple real-time measurements from the downhole measuring device; and synchronize the real-time data stratigraphically with the historical drilling data.

[0076] Embodiment 13: The drilling system of any one of embodiments 11 or 12, wherein the instructions cause the at least one processor to determine a probability of the real-time measurement being positioned stratigraphically within the region of interest.

[0077] Embodiment 14: The drilling system of any one of embodiments 11 through 13, wherein the instructions cause the at least one processor to: identify stratigraphic boundaries between stratigraphic sections of the stratigraphic signature; and determine a relationship betw een the real-time measurement and the stratigraphic boundaries.

[0078] Embodiment 15: The drilling system of embodiment 14, wherein the instructions cause the at least one processor to: display a vertically upward steering recommendation on the display device if the real-time measurement is proximate or under a lower stratigraphic boundary of the stratigraphic boundaries of the region of interest; and display a vertically downward steering recommendation on the display device if the real-time measurement is proximate or over an upper stratigraphic boundary' of the stratigraphic boundaries of the region of interest.

[0079] Embodiment 16: The drilling system of any one of embodiments 14 or 15, wherein the instructions cause the at least one processor to: receive real-time data including multiple real-time measurements from the downhole measuring device; identify real-time stratigraphic boundaries in the real-time data; and synchronize the real-time stratigraphic boundaries vertically with the stratigraphic boundaries between stratigraphic sections of the stratigraphic signature.

[0080] Embodiment 17: The drilling system of any one of embodiments 11 through 16, further comprising a steering device positioned proximate the downhole measuring device, wherein the instructions cause the at least one processor to control the steering device according to the steering recommendation.

[0081] Embodiment 18: A method of drilling a w ellbore, the method comprising: defining a stratigraphic signature of a formation based on historical data; receiving real-time data from a downhole tool; synchronizing the real-time data to the stratigraphic signature; receiving a real-time measurement from the downhole tool; determining a probability of the real-time measurement from the downhole tool being vertically positioned in a region of interest of the stratigraphic signature; and steering the downhole tool vertically if the probability of the real-time measurement being vertically positioned in the region of interest is determined to be low.

[0082] Embodiment 19: The method of embodiment 18, further comprising: identifying boundaries of the region of interest in the stratigraphic signature; and determining a stratigraphic relationship between the real-time measurement and the boundaries of the region of interest.

[0083] Embodiment 20: The method of embodiment 19, wherein identifying the boundaries of the region of interest comprises: identifying abrupt stratigraphic signature changes; identifying the abrupt stratigraphic signature changes associated with an upper boundary; and identifying the abrupt stratigraphic signature changes associated with a lower boundary.

[0084] Embodiments of the disclosure may be used to determine a true vertical depth of the BHA of a drilling assembly within a formation. When drilling horizontally, the true vertical depth of the BHA may change and the vertical depth of the desired stratigraphic section may change at different lateral positions. The embodiments of the disclosure may facilitate determining if a BHA has left or is approaching a boundary7of a stratigraphic section in realtime. These real-time determinations may facilitate early steering corrections, which may decrease the amount of drilling that occurs outside a desired stratigraphic section. This may result in increased efficiency and production of a wellbore.

[0085] The embodiments of the disclosure described above and illustrated in the accompanying drawing figures do not limit the scope of the invention, since these embodiments are merely examples of embodiments of the invention, which is defined by the appended claims and their legal equivalents. Any equivalent embodiments are intended to be within the scope of this disclosure. Indeed, various modifications of the present disclosure, in addition to those shown and described herein, such as alternative useful combinations of the elements described, may become apparent to those skilled in the art from the description. Such modifications and embodiments are also intended to fall within the scope of the appended claims and their legal equivalents.

Claims

CLAIMSWhat is claimed is:1 . A method of drilling a wellbore, the method comprising: collecting historical data from a formation; defining a stratigraphic signature of a region of interest in the historical data; identifying boundary conditions of the region of interest; capturing a real-time measurement from a downhole tool; comparing the real-time measurement to the historical data; and determining a probability of the real-time measurement from the downhole tool being stratigraphically positioned in the region of interest.

2. The method of claim 1, further comprising synchronizing the real-time measurement to the historical data before determining the probability of the real-time measurement from the downhole tool being stratigraphically positioned in the region of interest.

3. The method of claim 2, wherein synchronizing the real-time measurement to the historical data comprises synchronizing a real-time stratigraphic signature to the stratigraphic signature.

4. The method of claim 2, wherein synchronizing the real-time measurement to the historical data comprises converting a depth of the real-time measurement to a true vertical depth.

5. The method of claim 1, wherein identifying the boundary conditions comprises identifying stratigraphic signature changes defining boundaries between stratigraphic sections of the formation.

6. The method of claim 1 , wherein defining the stratigraphic signature of the region of interest in the historical data comprises defining the stratigraphic signature with a trendline fit to the historical data.

7. The method of claim 1, wherein collecting the historical data from the formation comprises converting depth measurements associated with the historical data to true vertical depths.

8. The method of any one of claims 1 through 7, further comprising: collecting real-time data including multiple real-time measurements; and fitting a trendline to the real-time data.

9. The method of claim 8, further comprising: comparing the trendline to the stratigraphic signature of the region of interest; and determining a relationship of the real-time measurement to the boundary conditions of the region of interest.

10. The method of claim 9, steering the downhole tool vertically toward the region of interest if the real-time measurement is determined to be proximate or across the boundary conditions of the region of interest.

11. A drilling system comprising: a downhole measuring device; a memory device storing historical drilling data from a similar formation; a display device; and non-transitory computer readable medium storing instructions thereon that, when executed by at least one processor, cause the at least one processor to perform steps comprising: define a stratigraphic signature of a region of interest in the historical drilling data; receive a real-time measurement from the downhole measuring device; compare the real-time measurement to the historical data; determine a relative vertical location of the downhole measuring device on the stratigraphic signature of the region of interest; and display a steering recommendation on the display device based on the relative vertical location of the downhole measuring device.

12. The drilling system of claim 11, wherein the instructions cause the at least one processor to: receive real-time data including multiple real-time measurements from the downhole measuring device; and synchronize the real-time data stratigraphically with the historical drilling data.

13. The drilling system of claim 11, wherein the instructions cause the at least one processor to determine a probability of the real-time measurement being positioned stratigraphically within the region of interest.

14. The drilling system of any one of claims 11 through 13, wherein the instructions cause the at least one processor to: identify stratigraphic boundaries between stratigraphic sections of the stratigraphic signature; and determine a relationship between the real-time measurement and the stratigraphic boundanes.

15. The drilling system of claim 14, wherein the instructions cause the at least one processor to: receive real-time data including multiple real-time measurements from the downhole measuring device; identify real-time stratigraphic boundaries in the real-time data; and synchronize the real-time stratigraphic boundaries vertically with the stratigraphic boundaries between stratigraphic sections of the stratigraphic signature.

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