Drilling and completion method for broken and soft low-permeability low-pressure coal seam coal bed gas horizontal well

Abstract

The invention relates to the technical field of coal mine safety mining, and discloses a well drilling and completion method for a broken and soft low-permeability low-pressure coal seam coalbed methane horizontal well, which comprises the following steps that a near-bit guide drilling tool combination is adopted for drilling, the combination comprises a bit, a near-bit short section and a gamma probe, and the distance between the gamma probe and the bit is 0.3-0.5 m; in the drilling process, a micro-step length monitoring device is adopted to collect and transmit drilling time data in real time, the measurement step length of a drilling time sensor of the monitoring device is 0.1 m, and drilling parameters are optimized in real time in combination with the drilling time data and a preset well wall stability model. By establishing a well wall stability prediction model of the horizontal well of the fractured and soft low-permeability coal seam, key parameters of drilling engineering are optimized, a well drilling and completion process technology of micro drilling, near-bit geosteering, low-pollution well wall strengthening and floating casing running of the fractured and soft low-permeability coal seam is formed, and the safe and efficient well drilling and completion target of the fractured and soft low-permeability coal seam is achieved.

Description

Technical Field

[0001] This invention relates to the field of safe coal mining technology, specifically to a drilling and completion method for horizontal wells in soft, low-permeability, and low-pressure coal seams with coalbed methane. Background Technology

[0002] Horizontal well drilling and completion methods for coalbed methane (CBM) are one of the core technologies for developing CBM resources. This technology increases the reservoir's drainage area by drilling long horizontal sections within the target coal seam, thereby achieving efficient extraction of CBM resources. Its application is mainly concentrated in coal mining areas, particularly for CBM reservoirs with complex geological structures, thin single-layer thickness, or where conventional vertical well development is not economically viable.

[0003] The following technical drawbacks exist in traditional drilling of extremely soft coal seams: Wellbore instability: Conventional drill string assemblies disturb the coal seam structure, leading to high collapse rates (e.g., collapse rate > 40% in Yangquan mining area) and narrow drilling fluid density window (only 0.05 g / cm³). 3 This makes it difficult to maintain wellbore stability. Trajectory control failure: Geological steering tools lag (gamma probe distance > 3m from drill bit), drilling logging step length is 1m, formation identification error is large, and coal seam encounter rate is less than 70%. Casing run-in jamming: Friction during casing run-in in horizontal sections exceeds limits (measured > 200kN), and the failure rate is high in long horizontal sections (e.g., > 800m). Existing technologies, such as patent CN102383788A, involve drilling parameter optimization, but do not solve the structural stability problem of extremely soft coal seams and lack integrated tool systems. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a drilling and completion method for horizontal wells in soft, low-permeability, and low-pressure coal seams, solving the problems of wellbore instability, low trajectory control accuracy, and casing jamming in the drilling of extremely soft coal seams in existing technologies.

[0005] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides a drilling and completion method for horizontal wells in soft, low-permeability, and low-pressure coal seams, comprising the following steps: The first step is drilling, which is carried out using a near-bit steered drilling assembly. The assembly includes a drill bit, a near-bit sub, and a gamma ray probe. The distance between the gamma ray probe and the drill bit is 0.3-0.5m, and they are rigidly connected via flange bolts. The near-bit sub has a built-in shock absorber.

[0006] Second step, real-time monitoring and control, in the drilling process, the micro-step monitoring device is used to collect and transmit the drilling time data in real time. The drilling time sensor of the monitoring device is integrated at the drill pipe coupling, the measurement step is 0.1m±0.02m, and the data transmission module adopts electromagnetic wave short transmission and mud pulse double channel. The micro-drilling time data collected in this step is combined with the preset wellbore stability model, when the drilling time data suddenly increases by more than 50%, the guiding system is triggered to correct the deviation, and the drilling fluid density parameter is optimized in real time.

[0007] Wellbore stability prediction model The establishment process is as follows: S1, obtain detailed historical data set of one or more drilled wells in the research area. The data set includes two categories of core data: Historical micro-drilling time data (t): retrieve and organize the drilling time logging data of the historical well in the drilling process. The original data is processed by data smoothing to eliminate random noise and abnormal fluctuations caused by equipment, and the trend data which can truly reflect the change of formation drillability is extracted.

[0008] Formation porosity data : This is the true value data. Through comprehensive interpretation of the cable logging data (density logging, neutron logging, acoustic logging) of the historical well, and combined with the analysis and test results of the core samples obtained from the formation in the laboratory, the formation porosity corresponding to different depth points is accurately calibrated.

[0009] S2, match and analyze the correlation of the two prepared data sets. The smoothed historical micro-drilling time data is taken as the independent variable, and the corresponding formation porosity data is taken as the dependent variable. The regression analysis or machine learning algorithm in mathematical statistics is used to find and establish the functional relationship or mapping relationship between the two, and finally solidify it into a mathematical model that can be quickly calculated, i.e. the prediction model . The model quantitatively describes the inherent correlation between drillability (represented by ) and rock looseness (represented by ) in the specific area of broken soft coal seam.

[0010] S3, use part of the historical data not involved in modeling as an independent verification set to test the established model , and verify its prediction accuracy and generalization ability. After verification, the model algorithm is deployed to the ground real-time drilling monitoring system.

[0011] When the micro-drilling time data suddenly increases by more than 50%, the system triggers the guiding system to correct the deviation, and adjusts the drilling fluid density in real time according to the model analysis results, to ensure the wellbore stability during drilling.

[0012] Third step, cementing operation, when running casing, low disturbance cementing structure is used for operation. The cementing structure includes injecting clean polymeric membrane anti-sloughing drilling fluid, adding a floating collar every 300 m in the casing horizontal section, and installing a rotating guide shoe at the front end of the casing, and rotating the rotating guide shoe at a speed of 30 rpm during running.

[0013] The second aspect of the application provides a structure system for drilling and completing horizontal wells in soft, low-permeability and low-pressure coal seams, which is used to realize the drilling and completion method described above. The system comprises: A near-bit steering assembly: including a drill bit, a near-bit sub, and a gamma probe. The distance between the gamma probe and the drill bit is 0.3-0.5 m, and they are rigidly connected by flange bolts. The near-bit sub is internally provided with a shock absorber for reducing the amplitude of drill tool vibration.

[0014] A micro-step length monitoring device: including a drilling time sensor and a data transmission module. The drilling time sensor is integrated at the drill pipe collar, with a sampling frequency of ≥10 Hz, and a measurement step of 0.1 m±0.02 m. The data transmission module uses electromagnetic wave short transmission and mud pulse dual channels, with a data transmission delay of less than 5 s.

[0015] A low disturbance cementing structure: including a clean polymeric membrane anti-sloughing drilling fluid injection unit, a floating collar, and a rotating guide shoe.

[0016] The drilling fluid injection unit is used to inject clean polymeric membrane anti-sloughing drilling fluid containing a nano-scale polymer membrane forming agent with a concentration of 3-5%.

[0017] The nano-scale polymer membrane forming agent is prepared from the following raw materials by weight: modified nanocellulose 20-30 parts, sulfonated phenolic resin 10-15 parts, acrylamide 5-10 parts, crosslinking agent N,N'-methylene bisacrylamide 0.1-0.3 parts, and deionized water 50-60 parts.

[0018] The method for preparing the nano-scale polymer membrane forming agent comprises the following steps: S1: dispersing modified nanocellulose and sulfonated phenolic resin in deionized water, stirring for 1 hour in a 60℃ water bath; S2: adding acrylamide monomer and crosslinking agent, purging with nitrogen for 30 minutes to remove oxygen; S3: adding initiator ammonium persulfate, heating to 70℃ for 4 hours to obtain the nano-scale polymer membrane forming agent emulsion.

[0019] The floating collar is filled with nitrogen with a density of 0.3 g / cm 3 .

[0020] The front end of the rotating guide shoe is provided with 3 groups of tungsten carbide rollers distributed at 120°, and the roller diameter is 30 mm.

[0021] The application provides a drilling and completion method for a horizontal well of a soft and broken low-permeability and low-pressure coal seam. 1. The application establishes a horizontal well wall stability prediction model for a soft and broken low-permeability and low-pressure coal seam, optimizes key drilling engineering parameters, forms a drilling and completion technology of "micro drilling time + near-bit geosteering + low-pollution strong well wall + floating casing running" for the soft and broken low-permeability coal seam, and realizes the safe and efficient drilling and completion goal of the soft and broken low-permeability coal seam.

[0022] 2. The application establishes a horizontal well wall stability prediction model for a soft and broken low-permeability and low-pressure coal seam, calculates the safe density window of a drilling fluid of a test well, and explains the mechanical mechanism of the instability of the horizontal well wall of the soft and broken coal seam; a horizontal well bore trajectory prediction model is constructed, a drilling tool assembly sensitivity analysis is performed, and a near-bit steering drilling tool assembly for the soft and broken coal seam is optimized.

[0023] 3. The micro drilling time measurement step of the application is accurate to 0.1 m, which is 10 times higher than the 1 m step of a conventional drilling time logging, and the gamma probe is only 0.5 m away from the drill bit, so that the integrated technology of "micro drilling time + near-bit geosteering" greatly improves the timeliness and accuracy of the formation identification.

[0024] 4. The application optimizes the horizontal well floating collar + rotating guide shoe running casing process, and the integrated technology of "low-pollution well wall cementing drilling fluid + floating casing running" ensures the stability of the well wall and reduces the casing running friction. DETAILED DESCRIPTION

[0025] Figure 1 It is a complete flowchart of the method of the embodiment of the application. Figure 2 It is a micro drilling time monitoring flowchart of the embodiment of the application. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the specification of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0027] Embodiment 1: Drilling and completion method for a horizontal well of a soft and broken low-permeability and low-pressure coal seam In this embodiment, the XJ-2L well in the Yangquan mining area with a hardness coefficient of 0.3 is taken as an example. The well is completed with a drilling depth of 1770 m and a horizontal section length of 971 m.

[0028] I. Pre-drilling preparation and scheme optimization Borehole stability prediction: Based on the pre-established borehole stability prediction model, combined with the formation parameters, the safe density window of the drilling fluid in this well is calculated to be 1.02-1.14 g / cm 3 .

[0029] Drilling assembly configuration: Φ152.4mm PDC bit is used as the drill bit. The drilling assembly is: Φ152.4mm PDC bit → near-bit short sub (length 1.2m, built-in shock absorber) → gamma probe (outer diameter 89mm). The gamma probe is rigidly connected to the near-bit short sub through flange bolts, ensuring that the distance between the gamma probe and the drill bit is 0.5m.

[0030] Drilling fluid configuration: Clean polymeric membrane anti-sloughing drilling fluid is configured, in which the concentration of nanoscale polymeric membrane forming agent is 4%.

[0031] II. Drilling and real-time regulation Micro-drilling time monitoring: During drilling, the micro-drilling time sensor integrated at the drill collar automatically collects micro-drilling time data at a step size of 0.1m±0.02m.

[0032] Data transmission and processing: The collected micro-drilling time data is transmitted to the ground system in real time through the electromagnetic wave short transmission and mud pulse dual-channel data transmission module with a delay of less than 5s.

[0033] Trajectory and parameter regulation: The ground system will receive the micro-drilling time data and input it into the pre-set borehole stability model for analysis. When the micro-drilling time data suddenly increases by more than 50%, the system triggers the steering system to correct the deviation, and adjusts the drilling fluid density in real time according to the model analysis results to ensure the borehole stability during drilling.

[0034] III. Cementing and casing running Drilling fluid circulation: Before running the casing, clean polymeric membrane anti-sloughing drilling fluid is circulated and injected to form a nanoscale protective film on the borehole wall.

[0035] Casing running: A floating collar is installed every 300m in the horizontal section of the casing, which is filled with nitrogen with a density of 0.3g / cm 3 . A rotating guide shoe is installed at the front end of the casing, which is provided with 3 groups of tungsten carbide rollers distributed at 120°, with a roller diameter of 30mm. During the running of the casing, the rotating guide shoe rotates at a speed of 30rpm to replace sliding friction with rolling friction.

[0036] Comparative Example 1 Compared with Example 1, the differences of the present comparative example are: Drilling assembly: A conventional drilling assembly is used, in which the distance between the gamma probe and the drill bit is greater than 3m, and the near-bit short sub does not have a built-in shock absorber.

[0037] Micro-drilling time monitoring: The conventional drilling time logging technology is adopted, and the measurement step is 1 m, and the micro-step monitoring device is not adopted.

[0038] Cementing and casing running: The conventional drilling fluid system is adopted, and the nanoscale polymer membrane forming agent is not contained, and the conventional guide shoe is used in casing running, and the floating function and the rotating function are not provided.

[0039] Test Example 1: Wellbore stability verification I. Experimental description The present test example aims to verify the technical effect of the method of the present application in improving the wellbore stability of the horizontal well in the broken soft coal seam.

[0040] Experimental object: Select two horizontal well sections with similar geological conditions in XJ-2L well (adopting the method of the present application) in Example 1 and the comparative well (adopting the conventional method) in Comparative Example 1 as the test objects.

[0041] Experimental steps: Safety density window determination: During drilling, the density value calculated by the formation stability prediction model is taken as the benchmark, the drilling fluid density is adjusted, and the shape, size and quantity of the returned cuttings are continuously monitored, and the upper and lower limits of the drilling fluid density when no large-scale wellbore sloughing or caving occurs are recorded, and the window width is calculated.

[0042] Caving rate calculation: After the drilling of the two test well sections is completed, the borehole is measured by using the multi-arm caliper, and the actual profile and volume (V 实际 ) of the borehole are obtained. According to the drill bit diameter (D) and the length (L) of the well section, the theoretical volume (V 理论 =π*(D / 2) 2 *L) of the borehole is calculated. The caving rate (η) is calculated by the following formula: η=(V 实际 -V 理论 ) / V 理论 ×100%.

[0043] Data recording: Record and compare the safety density window width and the average caving rate of the well section of the two test objects.

[0044] II. Experimental data The test results show that the technical scheme adopted in Example 1 has a significant improvement effect on the wellbore stability. The mechanism lies in that, first, the nanoscale polymer membrane forming agent in the clean polymer membrane anti-sloughing drilling fluid can form a dense and tough protective film on the wellbore surface. The protective film can effectively plug the micro-cracks of the broken soft coal seam, realize the physical isolation of the wellbore, and thus inhibit the hydration expansion and structure strength deterioration caused by the invasion of the drilling fluid filtrate into the formation, which is the direct reason for reducing the caving rate.

[0045] Secondly, the 0.1m precision drilling time data obtained by the micro-step monitoring device, combined with the low-delay stratum information of the near-bit gamma probe, makes the borehole wall stability prediction model The system can perform real-time calculation with high timeliness. When the model identifies that the stratum drillability changes, indicating that the borehole wall stability may decrease, the system can immediately adjust the drilling parameters to optimize the drilling fluid density and control the instability factor in the embryonic state. This active and real-time regulation method avoids the borehole wall damage caused by the mismatch between the drilling parameters and the stratum, thereby widening the safe density window of the drilling fluid.

[0046] In summary, the present application fundamentally changes the stress environment and chemical environment of the borehole wall by combining chemical plugging with physical support (polymer film) and real-time monitoring and active regulation (micro-drilling time + model). The shock absorber built in the near-bit sub further reduces the mechanical impact of drill tool vibration on the borehole wall. The synergy of chemical, physical and mechanical multiple actions collectively constitutes a comprehensive stability system for the borehole wall in the broken and soft coal seam, ultimately achieving a significant reduction in the hole collapse rate and a significant widening of the safe density window.

[0047] Test Example 2: Trajectory control precision and drilling efficiency verification The present test example aims to verify the technical effects of the method of the present application in improving the trajectory control precision of the horizontal well in the broken and soft coal seam and the coal seam drilling rate.

[0048] Experimental explanation: Experimental object: XJ-2L well in Example 1 (using the method of the present application) and the comparative well in Comparative Example 1 (using the conventional method) are selected as the test objects.

[0049] Experimental steps: Geosteering decision: for the well of Example 1, the geosteering decision is made based on the data transmitted in real time by the near-bit gamma probe and the micro-drilling time sensor; for the well of Comparative Example 1, the decision is made based on the conventional MWD (measurement while drilling) tool (the probe is more than 3m away from the drill bit) and the 1m step drilling time data.

[0050] Post-drilling trajectory verification: after the completion of drilling of each well, the final and high-precision stratum gamma curve is obtained by wireline logging, and the actual depth position of the coal seam roof and floor is accurately marked in combination with the drilling cuttings logging data.

[0051] Coal seam drilling rate calculation: the actual trajectory of the drill bit is compared with the marked coal seam position to accurately calculate the cumulative length of the drill bit trajectory inside the target coal seam (coal seam drilling length) in the horizontal section. The coal seam drilling rate (R) is calculated by the following formula: R = (coal seam drilling length / horizontal section total length) x 100%.

[0052] Data record: record and compare the total length of the horizontal section, the length of drilling in the coal seam and the calculated drilling rate of the coal seam of each test object.

[0053] Experimental data: The above experimental data shows that the technical scheme can significantly improve the drilling rate of the coal seam of the horizontal well in the broken soft coal seam. The mechanism is firstly that the response timeliness of the geosteering is fundamentally improved. The spacing between the gamma probe and the drill bit of the near-bit steering assembly is shortened to 0.5 m, which is much shorter than the spacing of more than 3 m in the conventional process. The detection point and the cutting point are almost coincident. This makes the geosteering system obtain the signal of the change of the stratum when the drill bit just contacts or penetrates the roof and floor of the coal seam, thereby greatly shortening the reaction time between the occurrence of the change of the stratum and the decision of the system to make a correction, and avoiding the long-distance invalid drilling of the drill bit outside the coal seam.

[0054] Secondly, the accuracy of the stratum identification is improved. The micro-step length monitoring device can collect drilling time data with a step length of 0.1 m, which is 10 times higher than the resolution of the conventional 1 m step length drilling time logging. The high-resolution drilling time data can finely reflect the subtle differences in drillability between the broken soft coal seam and the roof and floor rocks. By analyzing the change trend of the micro-drilling time data, the stratum boundary can be identified earlier and more accurately than the conventional method, providing a decision basis for the steering system to make fine trajectory adjustment, so that the drill bit can follow the center of the coal seam more stably.

[0055] In summary, the technical scheme integrates "micro-drilling time + near-bit geosteering" to build a high-timeliness and high-resolution stratum identification and trajectory control feedback system. The near-bit gamma probe solves the problem of detection delay, and the micro-step length drilling time solves the problem of identification accuracy. Through the double-channel data transmission module with a delay of less than 5 s, the ground system can ensure accurate and real-time data for trajectory regulation and control.

[0056] Test example 3: verification of casing running friction The present test example aims to verify the technical effect of the method of the present application in reducing the casing running friction of the horizontal well in the broken soft coal seam.

[0057] Experimental explanation: Test object: XJ-2L well in example 1 (using the method of the present application) and the comparative well in comparative example 1 (using the conventional method) are selected as the test objects.

[0058] Experimental steps: Hardware configuration: in the well of example 1, a float collar is installed every 300 m in the horizontal section, and a rotating guide shoe is installed at the front end of the casing string; in the well of comparative example 1, a conventional guide shoe is used to configure the casing string.

[0059] Friction monitoring: During the running of casing in two wells, the hook load changes during the whole process of running casing string were recorded by the weight indicator sensor at the wellhead.

[0060] Data calculation: The measured hook load was compared with the theoretical hanging weight of the casing string in the drilling fluid, and the maximum friction generated during running was calculated. Maximum friction = Theoretical hanging weight of casing string - Minimum measured hook load.

[0061] Success rate record: Whether the casing in two wells could be run to the predetermined depth at one time was recorded.

[0062] Data record: The length of the horizontal section, the maximum measured friction and the success rate of running at one time of the two test objects were recorded and compared.

[0063] Experimental data: The above experimental data show that the technical solution can greatly reduce the friction during the running of casing and ensure the success of the operation. The mechanism of reducing friction is reflected in two aspects. First, the floating collar and the rotating guide shoe in the low disturbance cementing structure directly change the stress state of the casing string. The floating collar filled with 0.3g / cm 3 density nitrogen provides buoyancy for the casing string along the horizontal section, which offsets part of the casing weight, thereby reducing the normal pressure between the casing and the well wall, and according to the principle of friction mechanics, the reduction of normal pressure directly leads to the reduction of frictional resistance. At the same time, the rotating guide shoe at the front end converts the sliding friction between the casing front end and the well wall into rolling friction through the tungsten carbide rollers on it and its own rotating movement, and since the rolling friction coefficient is much lower than the sliding friction coefficient, the resistance at the front end is effectively reduced when passing through the curved section or irregular section of the borehole.

[0064] Secondly, the smooth running of the casing also benefits from the regular wellbore formed by the previous drilling operation. As shown in Test Example 1, by using clean polyfilm anti-sloughing drilling fluid, the collapse and peeling of the well wall are effectively inhibited, forming a wellbore with uniform diameter and smooth inner wall. A regular wellbore reduces the mechanical sticking points caused by changes in well diameter, steps or accumulation of debris. Therefore, when the casing string equipped with floating collar and rotating guide shoe runs in such a high-quality wellbore, the geometric obstacles and irregular contacts it encounters are greatly reduced, which is an important prerequisite for reducing the total friction.

[0065] In summary, the technical scheme realizes systematic control of the casing running friction by integrated application of the low-pollution well cementing wall drilling fluid and floating casing running. The floating collar reduces the overall weight burden from a macro perspective, the rotating guide shoe solves the problem of passing through obstacles from the front end, and the high-quality wellbore provides a low-resistance channel for the entire process. The synergistic effect of the three will lead to the optimization of the mechanical factors (positive pressure, friction coefficient) and geometric factors (irregular wellbore) of casing running sticking, thereby enabling the one-time successful running of the casing in the long horizontal section.

Claims

1. A method for drilling and completing a coalbed methane horizontal well in a soft, low permeability, low pressure coal seam, characterized in that, The method comprises the following steps: a) drilling operation: drilling with near-bit steering assembly, which comprises drill bit, near-bit sub and gamma probe, the distance between the gamma probe and the drill bit is 0.3-0.5m; b) real-time monitoring and control: during drilling, real-time drilling time data is collected and transmitted by micro-step monitoring device, the drilling time sensor of the monitoring device measures the step length of 0.1m, and the drilling time data is combined with the preset wellbore stability model to optimize the drilling parameters in real time; c) cementing operation: when the casing is lowered, low disturbance cementing structure is used for operation, which comprises injection of clean polymeric membrane anti-sloughing drilling fluid, floating collar and rotating pilot shoe.

2. The drilling and completion method of a horizontal coalbed gas well in soft low-permeability and low-pressure coal seams according to claim 1, characterized in that, In the near-bit steering assembly, the gamma probe and the near-bit sub are rigidly connected by flange bolts, and the near-bit sub is provided with a shock absorber.

3. The method according to claim 1, characterized in that, In the micro-step monitoring device, the sampling frequency of the drilling time sensor is ≥10Hz, the data transmission module uses electromagnetic wave short transmission and mud pulse double channel for data transmission, and the delay is <5s.

4. The method according to claim 1, characterized in that, In the cementing operation, the clean polymeric membrane anti-sloughing drilling fluid contains 3-5% nanoscale polymer membrane forming agent, which forms a protective film on the wellbore.

5. The method according to claim 1, wherein, In the cementing operation, one of the floating collar is installed every 300m of the horizontal section of the casing, and the collar is filled with nitrogen with a density of 0.3g / cm 3 .

6. The method according to claim 1, wherein, In the cementing operation, the rotating pilot shoe is provided with three groups of tungsten carbide rollers distributed at 120° at the front end, the diameter of the roller is 30mm, and the rotating pilot shoe rotates at a speed of 30rpm when the casing is lowered, thereby reducing the friction.

7. The method according to claim 1, wherein, The real-time monitoring and control step comprises: substituting the drilling time data collected by the micro-step monitoring device into the wellbore stability model: ； wherein, is a formation stability index, is a microdrill; When the micro-drilling time surge is >50%, the guiding system is triggered to correct the deviation.

8. The method according to claim 7, wherein, The method is suitable for very soft coal seams with a hardness coefficient of the coal seam of 0.1 to 0.3.

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