A method for optimizing wellbore trajectory design based on formation lithology

Abstract

The present invention discloses a method for optimizing wellbore trajectory design based on formation lithology, suitable for wellbore trajectory optimization in ultra-shallow horizontal well single-pass drilling. During the actual single-pass drilling of ultra-shallow horizontal wells, the actual drilling buildup rates using only one type of screw in well sections with different formations and lithologies vary significantly. By optimizing the wellbore trajectory based on formation lithology, the well sections in loose formations are optimized to have a low buildup rate, and the well sections in stable formations are optimized to have a high buildup rate. This allows the designed buildup rate to be close to the actual buildup rate during construction, facilitating trajectory control during actual drilling and effectively reducing the risk of trajectory loss of control.

Description

Technical Field

[0001] The present invention belongs to the technical field of directional drilling operations, and relates to a one-trip drilling technology for ultra-shallow horizontal wells, in particular to a method for optimizing the design of wellbore trajectories based on formation lithology. Background Art

[0002] For horizontal wells with ultra-shallow vertical depth (buried depth of 250-500m), the wellbore structure is a simple two-step drilling. Generally, the vertical wellbore of the first drilling is about 60-100m, and the wellhead is established after casing is lowered and cemented; the second drilling is completed in one trip to complete the drilling construction of the vertical well section + increased inclination section + horizontal section. Completing the second-stage drilling construction in one drilling trip can reduce the time of drilling and drilling, improve drilling efficiency, and save drilling cycles; the one-trip drilling tool combination can accurately grasp the reverse torsion angle and tool face of the screw, and can master the inclination ability of the drilling tool combination of this trip, and continuously and effectively control the trajectory through the combination of sliding drilling and compound drilling, avoiding the groping stage caused by replacing screws of different degrees or replacing the drilling tool combination, which is beneficial to trajectory control; due to the shallow burial depth of the formation, the formation has good drillability and fast drilling speed, and the mud treatment lags behind the drilling speed. The use of one-trip drilling technology can avoid drilling and drilling in the absence of a stable mud system and when the wellbore is unstable, and avoid the underground complexities such as well dredging, eyelet marking, and new eyelet caused by poor drilling, which is beneficial to underground safety.

[0003] Ultra-shallow horizontal wells, due to the shallow vertical depth of the target formation, require a high designed build rate (typically 7-10° / 30m). Currently, the wellbore trajectory design for ultra-shallow horizontal wells primarily utilizes a single-increment circular arc trajectory to maximize downward pressure on the build point and reduce the designed build rate. During the actual drilling of ultra-shallow horizontal wells in a second-run, single-pass process, only a single type and strength of screw drill tool is used to control the trajectory. Due to varying formation lithologies and drillability, the actual build rates vary significantly across different formations and well sections with different lithologies. In general, the actual build rate corresponds to the formation lithology as follows: In the early stages of directional drilling, the actual build rate is low due to shallow burial depth, loose formations, poor diagenesis, and loose formations. When drilling into loosely cemented sandstone and water-bearing intervals, the actual build rate is low. When drilling into stable mudstone intervals, the actual build rate is high. When drilling into the upper gray sandstone interval in the target formation, the actual build rate is high, and when drilling into the loose sandstone interval in the middle and lower parts of the target formation, the actual build rate is low. Implementing ultra-shallow horizontal wells according to a single-increment wellbore trajectory design without considering the geological factors of the designed well, when drilling into loose formations, the continuous directional build rate is still low or even does not increase, and the actual drilling build rate cannot meet the build rate requirements of the single-increment wellbore trajectory design, making trajectory control difficult and even leading to trajectory loss of control.

[0004] The wellbore trajectory design under the double-opening and single-trip drilling construction of ultra-shallow horizontal wells is optimized based on the formation lithology after fully understanding and analyzing the formation and lithology, so that the designed inclination rate is close to the actual inclination rate during construction, which is beneficial to trajectory control and can reduce the risk of trajectory loss of control. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for optimizing the design of wellbore trajectory based on formation lithology in order to address the deficiencies in the prior art.

[0006] The technical solution is as follows:

[0007] The following steps are involved:

[0008] (1) Collect the well history data of the wells drilled in the same block, calculate the actual drilling inclination rate of the same model and degree of screw in the well sections of various formations and lithologies in the wells drilled in the same block, and divide the actual inclination rate corresponding to the well section of loose formation and the actual inclination rate corresponding to the well section of stable formation into sections according to vertical depth;

[0009] (2) Based on the geological design of the construction well, the various stratum and lithology sections of the construction well are divided into loose formation sections and stable formation sections according to the vertical depth;

[0010] (3) Optimize the borehole trajectory of the construction well to be drilled. The well section in loose formation is optimized to have a low build rate, and the well section in stable formation is optimized to have a high build rate, so that the designed build rate is close to the actual build rate during construction. At the same time, the well section from the oil top to target A is optimized to have a low build rate.

[0011] Furthermore, in step (1), the actual drilling inclination rates of various formation lithology sections are counted, mainly to clarify the minimum inclination rate-maximum inclination rate range and the high-probability inclination rate range of the same model screw in the case of continuous orientation in loose formation sections, and to clarify the minimum inclination rate-maximum inclination rate range and the high-probability inclination rate range of the same model screw in the case of continuous orientation in stable formation sections.

[0012] Furthermore, in step (2), the formation lithology of the construction well is compared with the formation lithology of the drilled well according to the vertical depth from shallow to deep, and the construction well is divided into a loose formation well section and a stable formation well section according to the vertical depth.

[0013] Furthermore, in step (3), the wellbore trajectory of the construction well is optimized, and a multi-curvature and multi-constant tool face wellbore trajectory design model is adopted, and a "straight well section-the first inclination increase section (inclination rate 1, constant tool face angle 1)-the second inclination increase section (inclination rate 2, constant tool face angle 2)-the third inclination increase section (inclination rate 3, constant tool face angle 3)...+horizontal section" combination design is adopted.

[0014] Furthermore, in step (3), the wellbore trajectory of the construction well is optimized, and the corresponding build rate of each formation lithology well section is optimized to be set within the range of the lowest build rate to the highest build rate of the corresponding well section drilled in the same block, and as close as possible to the range of the most probable build rate of the wells drilled in the same block.

[0015] Furthermore, in step (3), the wellbore trajectory of the construction well is optimized, and the section from the oil top to the target well A is optimized to have a low inclination rate, which is conducive to exploring and searching for high-quality reservoirs. Once the high-quality reservoir is reached, the trajectory can be leveled in time and drilling can be switched to the horizontal section of the high-quality reservoir.

[0016] Furthermore, in step (3), the wellbore trajectory of the construction well is optimized. The thickness between the top oil vertical depth and the target vertical depth A is predicted based on relevant data to optimize the well inclination at the top oil vertical depth. If the thickness between the top oil vertical depth and the target vertical depth A is predicted to be thick, the top oil vertical depth is optimized to correspond to a small well inclination; if the thickness between the top oil vertical depth and the target vertical depth A is predicted to be thin, the top oil vertical depth is optimized to correspond to a large well inclination. The optimized top oil vertical depth orientation is the final orientation of the horizontal section. The purpose is to drill to the high-quality reservoir vertical depth as quickly as possible while coping with the uncertainty of the thickness from the top oil to the high-quality reservoir, and to avoid the risk of drilling through the high-quality reservoir due to the sudden encounter of a high-quality reservoir that is too loose and does not increase inclination.

[0017] The beneficial effects of the present invention are:

[0018] Wellbore trajectory optimization for single-trip drilling of ultra-shallow horizontal wells. During the actual single-trip drilling of ultra-shallow horizontal wells, the actual drilling build rates using only one type of screw vary significantly across well sections with different formations and lithologies. By optimizing the wellbore trajectory based on formation lithology, with low build rates for sections in loose formations and high build rates for sections in stable formations, the designed build rate is aligned with the actual build rate during operation, facilitating actual drilling trajectory control and effectively reducing the risk of trajectory loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of a method for optimizing wellbore trajectory design based on formation lithology. DETAILED DESCRIPTION

[0020] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0021] Refer to the attached Figure 1 , this example mainly includes the following wellbore trajectory optimization design steps:

[0022] Step (1): Collect the well history data of the P6 block, calculate the actual drilling inclination rate of the 197mm type 1.75° screw in the 241.3mm borehole of the P6 block in various formation lithology sections, and divide the actual inclination rate corresponding to the loose formation section and the actual inclination rate corresponding to the stable formation section according to the vertical depth, see Table 1.

[0023] Table 1 Actual build-up rates for well sections with different vertical depths and lithologies in the P6 block

[0024]

[0025] Step (2): The formation lithology of the construction well P6-1 was compared with the formation lithology of the drilled wells in the P6 block from shallow to deep according to the vertical depth. The construction wells were divided into loose formation well sections and stable formation well sections according to the vertical depth, as shown in Table 2.

[0026] Step (3): Optimize the well section in the loose formation of the construction well P6-1 to a low build rate and the well section in the stable formation to a high build rate, so that the designed build rate is close to the actual build rate during construction, see Table 2.

[0027] Table 2 Division of formation and well sections in well p6-1 and optimized inclination ratios to be drilled in the corresponding well sections

[0028]

[0029]

[0030] The steps for optimizing wellbore trajectory design and calculation are as follows:

[0031] 1) Calculate the well inclination and azimuth of the target point connection line

[0032] Assume that the vertical depth, north-south, and east-west coordinates of the given target points A and B are: D a 、N a 、E a and D b 、N b 、E b , then the well inclination angle a and azimuth angle φ of the two target points can be calculated.

[0033]

[0034]

[0035] 2) Given the vertical depth at the build point and the vertical depth at the end of the first ramping section, and given the build rate and tool face angle of the first ramping section, there are many known solutions to calculate the wellbore inclination, azimuth, north-south coordinate increment, and east-west coordinate increment at the end of the first ramping section;

[0036] 3) Given the top oil vertical depth, target A vertical depth, well inclination, and azimuth, and given the top oil vertical depth and well inclination, and the top oil vertical depth azimuth as target A azimuth, there are many known solutions to calculate the north-south coordinate increment, east-west coordinate increment, and the inclination rate of the well section from the top oil to target A;

[0037] 4) Given the vertical depths at the end of the second and third inclination sections, the north-south coordinate increments, east-west coordinate increments, and the second and third section buildup rates at the end of the second and third inclination sections can be calculated using the parameters in steps 2) and 3) using numerous known methods.

[0038] 5) The final data satisfies the following equation group (1).

[0039]

[0040] Where X, Y, Z, a, and φ represent east-west, north-south, vertical depth, well inclination, and azimuth, respectively; the subscripts A and kop represent target point A and inclination point, respectively; the subscripts 1, 2, and n represent the first, second, and nth sections of the profile design, respectively.

[0041] 6) After all parameters are calculated, the optimized design data of the wellbore trajectory of construction well P6-1 are shown in Table 3.

[0042] Table 3 P6-1 Wellbore Trajectory Optimization Design Data

[0043]

[0044] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for optimizing wellbore trajectory design based on formation lithology, characterized in that The implementation process is as follows: Step (1): Collect the well history data of the wells drilled in the same block, calculate the actual drilling inclination rate of the same model and degree of screw in the well sections of various formations and lithologies in the wells drilled in the same block, and divide the actual inclination rate corresponding to the loose formation section and the actual inclination rate corresponding to the stable formation section into sections according to the vertical depth; Step (2): Based on the geological design of the construction well, the various stratum and lithology sections of the construction well are divided into loose formation sections and stable formation sections according to vertical depth; Step (3): Optimize the trajectory of the wellbore to be drilled in the construction well. The well section in the loose formation is optimized to have a low build rate, and the well section in the stable formation is optimized to have a high build rate, so that the designed build rate is close to the actual build rate during construction; optimize the well section from the oil top to the A target to have a low build rate; In step (1), the actual drilling buildup rates of various formation lithology sections are counted, and the minimum buildup rate-maximum buildup rate range and the high probability buildup rate range of the same model screw in the case of continuous directional drilling in loose formation sections are clarified. The minimum buildup rate-maximum buildup rate range and the high probability buildup rate range of the same model screw in the case of continuous directional drilling in stable formation sections are clarified. Step (3) wellbore trajectory optimization of the construction well adopts a multi-curvature multi-constant tool face wellbore trajectory design model, and adopts a "straight well section-first inclination section-second inclination section-third inclination section...+horizontal section" combination design, wherein the first inclination section has an inclination rate of 1 and a constant tool face angle of 1, the second inclination section has an inclination rate of 2 and a constant tool face angle of 2, and the third inclination section has an inclination rate of 3 and a constant tool face angle of 3; Step (3) wellbore trajectory optimization of the construction well is carried out. The thickness between the top oil vertical depth and the target vertical depth A is predicted based on relevant data to optimize the well inclination at the top oil vertical depth. If the thickness between the top oil vertical depth and the target vertical depth A is predicted to be thick, the top oil vertical depth is optimized to correspond to a small well inclination; if the thickness between the top oil vertical depth and the target vertical depth A is predicted to be thin, the top oil vertical depth is optimized to correspond to a large well inclination; the optimized top oil vertical depth azimuth is the final azimuth of the horizontal section.

2. The method for optimizing wellbore trajectory design based on formation lithology according to claim 1, characterized in that: Step (2) compares the formation lithology of the construction well with the formation lithology of the drilled well according to the vertical depth from shallow to deep, and divides the construction well into loose formation well section and stable formation well section according to the vertical depth.

3. The method for optimizing wellbore trajectory design based on formation lithology according to claim 1, characterized in that: Step (3) Optimize the wellbore trajectory of the construction well, optimize the corresponding inclination rate of each formation lithology well section and set it within the range of the lowest inclination rate - the highest inclination rate of the corresponding well section drilled in the same block, and as close as possible to the inclination rate range of the drilled wells in the same block.

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