Deep sea shallow gas reservoir damage evaluation simulation experiment method

Abstract

The invention belongs to the technical field of petroleum engineering, and particularly relates to a deep sea shallow gas reservoir damage evaluation simulation experiment method. According to the deep-sea shallow gas reservoir damage evaluation simulation experiment method provided by the invention, deep-sea shallow gas reservoir damage evaluation simulation experiment research can be specifically carried out, and a basic condition is provided for optimizing and developing a drilling fluid system for protecting the deep-sea shallow gas reservoir. The deep-sea shallow gas reservoir damage evaluation simulation experiment method provided by the invention has the following advantages that the characteristics of under-compaction and poor lithology of the deep-sea shallow gas reservoir can be simulated; according to the method, the damage degree of the drilling fluid to the deep sea shallow gas reservoir is evaluated according to the change degree of the drilling fluid pollution to the permeability, the overall strength and the single-point strength of the simulated rock sample. The damage degree of the drilling fluid to the deep-sea shallow gas reservoir is analyzed from multiple angles, and inaccurate research results or one-sidedness caused by single permeability test are avoided.

Description

Technical Field

[0001] This invention belongs to the field of petroleum engineering technology, specifically relating to a simulation experiment method for evaluating damage to deep-sea shallow gas reservoirs. Background Technology

[0002] Shallow deep-sea gas holds great development potential. However, compared to conventional onshore and offshore oil and gas reservoirs, the depth of shallow deep-sea gas reservoirs is mostly within 300 meters below the seabed mudline. The unique sedimentary characteristics of the deep sea result in undercompacted shallow deep-sea gas reservoirs with low strength and high water content. These characteristics make shallow deep-sea gas reservoirs highly susceptible to reservoir damage during drilling, such as collapse, particle migration blockage, and sensitive damage. This can prevent the full release and acquisition of natural gas. In particular, deep-sea drilling is characterized by high investment, high difficulty, and high risk, and the safety and economic losses caused by reservoir damage are enormous.

[0003] Because obtaining formation cores and rock samples during drilling is very costly and cannot meet the needs of large-scale indoor systematic research, it is necessary to establish suitable methods to simulate the characteristics of deep-sea shallow gas reservoirs in order to conduct reservoir damage assessment experiments. However, due to the undercompactment and high water content of deep-sea shallow gas reservoirs, existing methods for simulating core preparation and reservoir damage assessment experiments cannot effectively simulate the characteristics of deep-sea shallow gas reservoirs and maintain good repeatability. This makes it impossible to propose targeted protection technologies for deep-sea shallow gas reservoirs and to design suitable drilling and completion fluids to ensure effective reservoir protection during drilling and completion.

[0004] Currently, for drilling operations in conventional oil and gas reservoirs, the petroleum industry has established a mature standard for reservoir damage assessment experiments—"Indoor Evaluation Method for Drilling Fluid and Completion Fluid Damage to Oil Reservoirs (SY / T6540-2021)." This method allows for experiments using actual reservoir cores or artificially sintered cores. The degree of damage to the reservoir by the drilling fluid is characterized by the recovery or change rate of permeability in the rock samples after drilling fluid contamination. Because conventional onshore and shallow-sea drilling produces rocks with good lithology and high compaction, indoor sintered cores can simulate conventional formations to a certain extent. However, deep-sea shallow gas reservoirs, due to undercompaction, have high water content, are loose and brittle, and indoor pressed and sintered cores cannot accurately simulate these characteristics, and their poor parallelism makes them unsuitable for experimental requirements. Summary of the Invention

[0005] The purpose of this invention is to provide a simulation experiment method for evaluating damage to shallow deep-sea gas reservoirs. The simulation experiment method for evaluating damage to shallow deep-sea gas reservoirs provided by this invention can be used to conduct targeted simulation experiments on damage to shallow deep-sea gas reservoirs.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a simulation experiment method for evaluating damage to deep-sea shallow gas reservoirs, including permeability testing, overall strength testing, and single-point strength testing of simulated rock samples from deep-sea shallow gas reservoirs before and after drilling fluid contamination. Parameters for evaluating the degree of damage to deep-sea shallow gas reservoirs include: the rate of change in permeability, the rate of change in overall strength, and the rate of change in single-point strength of the simulated rock samples before and after drilling fluid contamination. The simulated rock samples include framework particles and clay minerals. The framework particles include calcite and quartz sand. The particle size of the calcite is 80–200 mesh. The quartz sand includes coarse quartz sand, medium quartz sand, and fine quartz sand. The particle size of the coarse quartz sand is greater than 200 mesh and not greater than 80 mesh; the particle size of the medium quartz sand is greater than 500 mesh and not greater than 200 mesh; and the particle size of the fine quartz sand is greater than 2000 mesh and not less than 500 mesh.

[0008] Preferably, the mass ratio of coarse quartz sand, medium quartz sand and fine quartz sand is 3-4:3-4:2-3; and the mass ratio of calcite and quartz sand is 1-2:7-8.

[0009] Preferably, the clay minerals include montmorillonite and illite; the mass ratio of montmorillonite to illite is 1 to 2:1.

[0010] Preferably, the mass ratio of the quartz sand to the clay mineral is 7-8:1-2.

[0011] Preferably, the method for preparing the simulated rock sample includes the following steps: mixing the skeleton particles and clay minerals to obtain a mixture, filling the mixture into a soft metal tube to obtain a rock sample soft metal tube, and immersing the rock sample soft metal tube in simulated formation water until the water saturation of the rock sample is not less than 80% and the porosity is 30-40%.

[0012] Preferably, the filling includes the following steps: dividing the mixture into 4 to 5 equal parts, pouring one part of the mixture into a soft metal tube, pressing its upper surface to one-quarter or one-fifth of the mark with a metal rod and letting it stand, and then gradually adding the remaining 3 or 4 parts of the mixture in the same way.

[0013] Preferably, the permeability test of the simulated rock sample is performed using the static evaluation test method for drilling fluid damage in the laboratory evaluation method for drilling fluid and completion fluid damage to the oil reservoir; in the permeability test of the simulated rock sample, the confining pressure is 2 to 2.5 MPa and the displacement pressure difference is 0.5 to 1 MPa.

[0014] Preferably, the overall strength test of the simulated rock sample involves performing overall strength tests on the simulated rock sample before and after drilling fluid contamination. The overall strength test includes the following steps: placing the simulated rock sample in the overall strength test system, aligning the pressure gauge pointer with the 0 mark, rotating the upper rotating wheel to drive the pressure head downward to apply force to the simulated rock sample on the support frame, the pressure gauge pointer reading gradually increases until it reaches the peak value and no longer changes, stopping the rotation of the rotating wheel, reading the pressure peak value, and ending the experiment. The pressure peak value is then substituted into the strength calculation formula.

[0015] Preferably, the single-point strength test of the simulated rock sample measures the single-point penetration depth of the two end faces of the simulated rock sample before drilling fluid contamination and the simulated rock sample after drilling fluid contamination, and analyzes the single-point strength of the simulated rock sample.

[0016] Preferably, the single-point penetration depth testing method includes the following steps: adjusting the displacement knob of the top penetration depth testing device, slowly lowering the needle connecting rod so that the tip of the standard needle just contacts the surface of the simulated rock sample, conducting the experiment under a standard load of 160g, and automatically stopping the experiment after 5s or 10s, and reading the penetration depth of the standard needle into the simulated rock sample according to the dial; at least 3 points are selected for testing on each end face of the simulated rock sample, and the average value is the penetration depth of the corresponding end face.

[0017] This invention provides a simulation experiment method for evaluating damage to shallow deep-sea gas reservoirs. This method allows for targeted simulation experiments to assess damage to shallow deep-sea gas reservoirs, providing a foundation for optimizing and developing drilling fluid systems that protect these reservoirs.

[0018] The simulation experiment method for assessing damage to shallow gas reservoirs in the deep sea provided by this invention has the following advantages:

[0019] (1) This invention can simulate the characteristics of undercompacted and poor diagenesis of deep-sea shallow gas reservoirs, overcoming the shortcomings of traditional artificial pressing or sintering cores that cannot simulate undercompacted deep-sea shallow gas reservoirs.

[0020] (2) This invention evaluates the damage caused by drilling fluid to deep-sea shallow gas reservoirs by assessing the degree of change in permeability, overall strength, and single-point strength of simulated rock samples due to drilling fluid contamination. Traditional reservoir damage assessment experimental methods only consider changes in reservoir core permeability. Considering the softness and structural instability of deep-sea shallow gas reservoir rock samples, considering only permeability changes may mislead researchers and lead to incorrect judgments about the degree of damage to deep-sea shallow gas reservoirs. This invention comprehensively considers the influence of drilling fluid on the permeability, overall strength, and structure of shallow loose rock samples, analyzing the degree of damage caused by drilling fluid to deep-sea shallow gas reservoirs from multiple perspectives, avoiding inaccurate or one-sided research results due to a single permeability test. Specifically:

[0021] In the core flow test, a standard experimental method for reservoir damage assessment, the short length of the core means that if the internal structure is damaged, some rock particles may be carried out of the core by the drilling fluid. From a permeability perspective, this may appear as if cavities have formed within the core, and the permeability may not have decreased significantly, leading researchers to mistakenly believe that the drilling fluid has not damaged the reservoir. However, in reality, the internal structure has been damaged or even collapsed, causing reservoir damage. Furthermore, the damaged and loosened rock particles infiltrate the reservoir with the drilling fluid, causing blockages within the reservoir – a phenomenon that traditional core flow tests cannot reflect or measure.

[0022] (3) This invention analyzes the damage patterns of drilling fluid treatment agents, drilling fluid formulations and drilling fluid performance parameters to deep-sea shallow gas reservoirs through experimental simulation, providing technical support for the design, selection and development of drilling fluid treatment agents and system formulations that effectively protect deep-sea shallow gas reservoirs. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the overall strength testing system for rock samples;

[0025] Figure 2 This is a schematic diagram of the top penetration test device;

[0026] Figure reference numerals: 1 is the rotating wheel, 2 is the connecting rod, 3 is the pressure gauge, 4 is the support frame, 5 is the pressure head, 6 is the simulated rock sample for overall strength testing, 7 is the displacement knob, 8 is the needle connecting rod, 9 is the dial, 10 is the standard part, 11 is the standard needle, and 12 is the simulated rock sample for single-point penetration depth testing. Detailed Implementation

[0027] This invention provides a simulation experiment method for evaluating damage to deep-sea shallow gas reservoirs, including permeability testing, overall strength testing, and single-point strength testing of simulated rock samples from deep-sea shallow gas reservoirs before and after drilling fluid contamination. Parameters for evaluating the degree of damage to deep-sea shallow gas reservoirs include: the rate of change in permeability, the rate of change in overall strength, and the rate of change in single-point strength of the simulated rock samples before and after drilling fluid contamination. The simulated rock samples include framework particles and clay minerals. The framework particles include calcite and quartz sand. The particle size of the calcite is 80–200 mesh. The quartz sand includes coarse quartz sand, medium quartz sand, and fine quartz sand. The particle size of the coarse quartz sand is greater than 200 mesh and not greater than 80 mesh; the particle size of the medium quartz sand is greater than 500 mesh and not greater than 200 mesh; and the particle size of the fine quartz sand is greater than 2000 mesh and not less than 500 mesh.

[0028] In this invention, the specific ratio of coarse quartz sand, medium quartz sand, and fine quartz sand is determined based on the mineral composition characteristics of the simulated deep-sea shallow gas reservoir; the mass ratio of coarse quartz sand, medium quartz sand, and fine quartz sand can be 3-4:3-4:2-3, specifically 3:3:2; the mass ratio of calcite to quartz sand can be 1-2:7-8, specifically 1.5:7.5.

[0029] In this invention, the clay minerals may include montmorillonite and illite; the specific ratio of montmorillonite and illite is determined based on the mineral composition characteristics of the simulated deep-sea shallow gas reservoir; the mass ratio of montmorillonite to illite may be 1 to 2:1.

[0030] In this invention, the specific ratio of the quartz sand and clay minerals is determined based on the mineral composition characteristics of the simulated deep-sea shallow gas reservoir; the mass ratio of the quartz sand and clay minerals can be 7-8:1-2, specifically 7.5:1.5.

[0031] In this invention, the method for preparing the simulated rock sample may include the following steps: mixing skeletal particles and clay minerals to obtain a mixture, filling the mixture into a soft metal tube to obtain a rock sample soft metal tube, and immersing the rock sample soft metal tube in simulated formation water until the water saturation of the rock sample is not less than 80% and the porosity is 30-40%, which is consistent with the rock sample characteristics of deep-sea shallow gas reservoirs.

[0032] In this invention, the total mass of the mixture can be 40-50g, specifically 45g.

[0033] In this invention, the filling process may include the following steps: dividing the mixture into 4 to 5 equal parts, pouring one part of the mixture into a soft metal tube, pressing its upper surface to one-quarter or one-fifth of the mark with a metal rod and letting it stand, and then gradually adding the remaining 3 or 4 parts of the mixture in the same way.

[0034] In this invention, the settling time can be 5 to 10 minutes, specifically 7 minutes.

[0035] In this invention, the diameter of the flexible metal tube can be 2.54 cm, the thickness can be less than 1.5 mm, and metal filters can be installed at both ends; the pore size of the metal filter can be 2000 mesh; the material of the flexible metal tube can be aluminum or copper.

[0036] In this invention, the soaking time can be 48 hours.

[0037] In this invention, the permeability test of the simulated rock sample can refer to the static evaluation test method of drilling fluid damage in the "Indoor Evaluation Method for Damage to Oil Reservoir by Drilling Fluid and Completion Fluid (SY / T 6540-2021)"; the permeability test of the simulated rock sample may include the following steps: placing the simulated rock sample in a device with core flow test function, testing the permeability of the simulated rock sample before and after static damage by drilling fluid, and calculating the permeability change rate.

[0038] In this invention, the confining pressure in the permeability test of the simulated rock sample can be 2–2.5 MPa, and the displacement pressure difference can be 0.5–1 MPa. By setting these parameters, this invention better adapts to the strong stress sensitivity caused by the loose structure of deep-sea shallow gas reservoirs.

[0039] In this invention, the overall strength test of the simulated rock sample can be performed on simulated rock samples before and after drilling fluid contamination. The overall strength test can include the following steps: placing the simulated rock sample in the overall strength test system, aligning the pointer of pressure gauge 3 with the 0 mark, rotating the upper rotating wheel 1 to drive the pressure head 5 downward to apply force to the simulated rock sample on the support frame 4, the reading of the pressure gauge 3 pointer gradually increases until it reaches a peak value and no longer changes, stopping the rotation of the rotating wheel 1, reading the pressure peak value, and ending the experiment. The pressure peak value is then substituted into the strength calculation formula. The overall strength test system of the rock sample includes a rotating wheel 1, a connecting rod 2, a pressure gauge 3, a support frame 4, and a pressure head 5. The rotating wheel 1 and the pressure gauge 3 are connected by the connecting rod 2, and the pressure gauge 3 and the pressure head 5 are connected by the support frame 4 (e.g., Figure 1 (As shown).

[0040] In this invention, the formula for calculating the strength is shown in Equation I:

[0041]

[0042] In Equation I, P represents the overall strength of the simulated rock sample, in kPa; F represents the maximum pressure the simulated rock sample can withstand, in N; and A represents the cross-sectional area of ​​the simulated rock sample, in m³. 2 .

[0043] In this invention, the overall strength change rate of the simulated rock sample is: (overall strength of the simulated rock sample before drilling fluid contamination - overall strength of the simulated rock sample after drilling fluid contamination) / overall strength of the simulated rock sample before drilling fluid contamination × 100%.

[0044] The greater the overall strength change rate of the simulated rock sample, the greater the damage to the structure and strength of the simulated rock sample caused by the drilling fluid, and the greater the reservoir damage caused.

[0045] In this invention, the single-point strength test of the simulated rock sample can test the single-point penetration depth of the two end faces of the simulated rock sample before drilling fluid contamination and the simulated rock sample after drilling fluid contamination, and analyze the single-point strength of the simulated rock sample.

[0046] In this invention, the single-point penetration depth testing method may include the following steps: adjusting the displacement knob 7 of the top penetration depth testing device, slowly lowering the needle connecting rod 8 so that the tip of the standard needle 11 just contacts the surface of the simulated rock sample 12, conducting the experiment under a standard component 10 load (the standard component 10 is loaded on the standard pointer, and the weight of the standard component 10 is used to press down), and the experiment automatically stops after 5s or 10s. The depth of the standard needle 11 penetrating the simulated rock sample is read according to the dial 9; the top penetration depth testing device includes the displacement knob 7, needle connecting rod 8, dial 9, standard component 10 and standard needle 11 (e.g., ...) connected in series. Figure 2 (As shown).

[0047] In this invention, the piercing of the simulated rock sample can be performed at least 3 points on each end face, and the average value is the piercing depth of the corresponding end face.

[0048] In this invention, the single-point strength change rate of the simulated rock sample is: (single-point penetration depth of the simulated rock sample after drilling fluid contamination - single-point penetration depth of the simulated rock sample before drilling fluid contamination) / single-point penetration depth of the simulated rock sample before drilling fluid contamination × 100%.

[0049] The greater the rate of change in intensity at a single point, the greater the impact of the drilling fluid on the simulated rock sample, and the greater the damage caused.

[0050] To further illustrate the present invention, the following detailed description of the invention's solutions, in conjunction with the accompanying drawings and embodiments, is provided, but should not be construed as limiting the scope of protection of the present invention.

[0051] Example 1

[0052] Based on the formation mineral composition characteristics of the target deep-sea shallow gas reservoir, simulated rock samples were prepared by mixing quartz sand, calcite and clay minerals (montmorillonite and illite in a mass ratio of 1:1) in a mass ratio of 7:1:2.

[0053] Weigh out 40g of quartz sand, calcite, montmorillonite, and illite, and mix them thoroughly in a beaker. Divide the mixed simulated rock sample into four equal portions. Pour one portion into an aluminum tube, press its upper surface to one-quarter mark using a metal rod, and let it stand for 5 minutes. Then, gradually add the remaining three portions of simulated rock sample in the same way, filling the tube gradually until the simulated rock sample is complete. Seal both ends with a 2000-mesh sieve. Immerse the simulated rock sample in a beaker filled with simulated formation water for 48 hours until the water saturation of the simulated rock sample is not less than 80% and the porosity is 30-40%, which is consistent with the characteristics of rock samples from deep-sea shallow gas reservoirs.

[0054] The drilling fluid formulation tested consisted of: water + 0.2 wt% xanthan gum thickener XC + 0.5 wt% polyanionic cellulose filtration reducer PAC-LV.

[0055] The permeability testing method for simulated rock samples refers to the static evaluation test method for drilling fluid damage in the "Indoor Evaluation Method for Damage to Oil Reservoir by Drilling Fluid and Completion Fluid (SY / T6540-2021)". The prepared simulated rock samples are placed in equipment with core flow test function, the confining pressure is set to 2.5 MPa and the displacement pressure difference is 1 MPa, the permeability of the simulated rock samples before and after static damage by drilling fluid is tested, and the permeability change rate is calculated.

[0056] The test method for the overall strength of the simulated rock sample is as follows: Place the simulated rock sample in the overall strength test system, align the pointer of pressure gauge 3 with the 0 mark, rotate the upper rotating wheel 1 to drive the pressure head 5 to apply force downward to the simulated rock sample, and the reading of the pointer of pressure gauge 3 gradually increases until it reaches the peak value and no longer changes. Stop rotating the rotating wheel 1, read the pressure peak value, and the experiment ends. Substitute the pressure peak value into the strength calculation formula, and the overall strength change rate of the rock sample is: (overall strength of the simulated rock sample before drilling fluid contamination - overall strength of the simulated rock sample after drilling fluid contamination) / overall strength of the simulated rock sample contaminated by drilling fluid × 100%.

[0057] The single-point strength test method for simulated rock samples is as follows: The penetration depth of two end faces of simulated rock samples that have not been contaminated by drilling fluid and those that have been contaminated by drilling fluid is tested separately, and the single-point strength of the simulated rock samples is analyzed. The single-point penetration depth test method is as follows: Adjust the displacement knob 7 of the top penetration depth testing device, slowly lower the needle connecting rod 8, so that the tip of the standard needle 11 just contacts the surface of the simulated rock sample 12. The experiment is conducted under a load of 160g, and the experiment automatically stops after 5 seconds. The penetration depth of the standard needle 11 into the simulated rock sample is read from the dial 9. At least 3 points are selected for testing on each end face, and the average value is taken as the penetration depth of the end face. The single-point strength change rate of the simulated rock sample is: (Single-point penetration depth of the simulated rock sample after drilling fluid contamination - Single-point penetration depth of the simulated rock sample before drilling fluid contamination) / Single-point penetration depth of the simulated rock sample before drilling fluid contamination × 100%.

[0058] Example 2

[0059] Based on the formation mineral composition characteristics of the target deep-sea shallow gas reservoir, simulated rock samples were prepared by mixing quartz sand, calcite and clay minerals (montmorillonite and illite in a mass ratio of 1:1) in a mass ratio of 7:1:2.

[0060] Weigh out 40g of quartz sand, calcite, montmorillonite, and illite, and mix them thoroughly in a beaker. Divide the mixed simulated rock sample into four equal portions. Pour one portion into an aluminum tube, press its upper surface to one-quarter mark using a metal rod, and let it stand for 5 minutes. Then, gradually add the remaining three portions of simulated rock sample in the same way, filling the tube gradually until the simulated rock sample is complete. Seal both ends with a 2000-mesh sieve. Immerse the simulated rock sample in a beaker filled with simulated formation water for 48 hours until the water saturation of the simulated rock sample is not less than 80% and the porosity is 30-40%, which is consistent with the characteristics of rock samples from deep-sea shallow gas reservoirs.

[0061] The drilling fluid formulation tested consisted of: water + 0.2 wt% xanthan gum thickener XC + 0.5 wt% carboxymethyl cellulose filtration reducer CMC-LV + 15 wt% NaCl.

[0062] The testing methods for permeability testing, overall strength testing, and single-point strength testing of simulated rock samples are the same as those in Example 1.

[0063] Example 3

[0064] Based on the formation mineral composition characteristics of the target deep-sea shallow gas reservoir, simulated rock samples were prepared by mixing quartz sand, calcite and clay minerals (montmorillonite and illite in a mass ratio of 1:1) in a mass ratio of 7:1:2.

[0065] Weigh out 40g of quartz sand, calcite, montmorillonite, and illite, and mix them thoroughly in a beaker. Divide the mixed simulated rock sample into four equal portions. Pour one portion into an aluminum tube, press its upper surface to one-quarter mark using a metal rod, and let it stand for 5 minutes. Then, gradually add the remaining three portions of simulated rock sample in the same way, filling the tube gradually until the simulated rock sample is complete. Seal both ends with a 2000-mesh sieve. Immerse the simulated rock sample in a beaker filled with simulated formation water for 48 hours until the water saturation of the simulated rock sample is not less than 80% and the porosity is 30-40%, which is consistent with the characteristics of rock samples from deep-sea shallow gas reservoirs.

[0066] The drilling fluid formulation tested consisted of: water + 0.2 wt% polyacrylamide (PAM) + 1 wt% starch filtration reducer + 2 wt% bitumen + 5 wt% ethylene glycol.

[0067] The testing methods for permeability testing, overall strength testing, and single-point strength testing of simulated rock samples are the same as those in Example 1.

[0068] Example 4

[0069] Based on the formation mineral composition characteristics of the target deep-sea shallow gas reservoir, simulated rock samples were prepared by mixing quartz sand, calcite and clay minerals (montmorillonite and illite in a mass ratio of 1:1) in a mass ratio of 8:1:1.

[0070] Weigh out 40g of quartz sand, calcite, montmorillonite, and illite, and mix them thoroughly in a beaker. Divide the mixed simulated rock sample into four equal portions. Pour one portion into an aluminum tube, press its upper surface to one-quarter mark using a metal rod, and let it stand for 5 minutes. Then, gradually add the remaining three portions of simulated rock sample in the same way, filling the tube gradually until the simulated rock sample is complete. Seal both ends with a 2000-mesh sieve. Immerse the simulated rock sample in a beaker filled with simulated formation water for 48 hours until the water saturation of the simulated rock sample is not less than 80% and the porosity is 30-40%, which is consistent with the characteristics of rock samples from deep-sea shallow gas reservoirs.

[0071] The drilling fluid formulation tested was the same as in Example 1, consisting of: water + 0.2 wt% xanthan gum thickener XC + 0.5 wt% polyanionic cellulose filtration reducer PAC-LV.

[0072] The testing methods for permeability testing, overall strength testing, and single-point strength testing of simulated rock samples are the same as those in Example 1.

[0073] Test Example 1

[0074] The test results of Examples 1 to 4 are shown in Table 1. The reservoir damage data of the deep-sea shallow gas reservoirs calculated based on the results in Table 1 are shown in Table 2.

[0075] Table 1. Test results of simulation experiments for damage assessment of deep-sea shallow gas reservoirs in Examples 1-4.

[0076]

[0077] Table 2 Analysis of Experimental Results for Damage Assessment of Deep-Sea Front Reservoirs

[0078] Example Permeability change rate / % Overall strength change rate / % Penetration depth change rate / % Example 1 35.15 18.53 13.07 Example 2 49.95 22.06 16.79 Example 3 29.34 10.32 7.07 Example 4 31.33 16.56 11.50

[0079] As can be seen from Tables 1 and 2, for the simulated rock samples prepared by methods 1 to 3, the permeability is maintained at 1.798 to 1.892 mD, the overall strength is maintained at 105.23 to 110.55 kPa, and the average penetration depth is maintained at 2.80 to 2.83 mm, indicating that the simulated rock samples prepared by this invention have good parallelism.

[0080] For Example 1, the permeability change rate after drilling fluid contamination was 35.15%, while for Example 2 it was 49.95% and for Example 3 it was 29.34%. This means that from a permeability perspective, the drilling fluid in Example 2 had a significantly greater impact on the reservoir than in Examples 1 and 3. Furthermore, based on the change rates of the overall strength and penetration depth of the simulated rock samples, Example 3 had the lowest change rates in both, indicating that the drilling fluid in Example 3 caused the least contamination to the reservoir from all three parameter perspectives. In contrast, the change rates of the overall strength of the simulated rock samples after drilling fluid contamination in Examples 1 and 2 were 18%. The penetration depth changes were 13.07% and 16.79%, respectively, with a decrease of 0.53% and 22.06%. This means that under the same simulated rock sample conditions, the damage caused by the drilling fluid in Example 1 to the simulated rock sample was similar to that in Example 2, and not as significant as the difference in permeability damage rate. In other words, if only considering the traditional permeability change rate, the drilling fluid in Example 1 caused far less damage to the reservoir than the drilling fluid in Example 2. However, in reality, the impact of the drilling fluid in Example 1 on the strength and framework of the simulated rock sample after contamination was similar to that in Example 2. Using permeability change rate as the evaluation index alone might lead researchers to incorrectly judge the reservoir damage caused by the drilling fluid. Comparison of Examples 1-3 shows that the drilling fluid in Example 3 caused the least damage to the reservoir.

[0081] Furthermore, the drilling fluid used in Example 4 was the same as that in Example 1, the only difference being the mineral composition of the simulated rock samples. It can be seen that, due to the lower clay mineral content in the simulated rock samples, the permeability of the simulated rock samples prepared in Example 4 was higher than that prepared in Example 1. However, due to the lack of clay minerals as a binder, the overall strength of the simulated rock samples prepared in Example 4 was slightly lower than that in Example 1, and the penetration depth was also deeper, meaning the strength at individual points was also lower. After being contaminated with the same drilling fluid as in Example 1, the permeability change rate, overall strength change rate, and penetration depth change rate of the simulated rock samples in Example 4 were all slightly lower than those in Example 1. This may be because the lower clay mineral content in the simulated rock samples in Example 4 resulted in less sensitive damage due to clay mineral hydration or dehydration, manifesting as less reservoir damage, but the results were not significantly different.

[0082] As can be seen from the above embodiments, the deep-sea shallow gas reservoir damage assessment simulation experiment method provided by the present invention can carry out targeted deep-sea shallow gas reservoir damage assessment simulation experiment research, and provide basic conditions for the selection and development of drilling fluid systems to protect deep-sea shallow gas reservoirs.

[0083] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A simulation experimental method for assessing damage to shallow deep-sea gas reservoirs, characterized in that, This includes permeability testing, overall strength testing, and single-point strength testing of simulated rock samples from deep-sea shallow gas reservoirs before and after drilling fluid contamination; Parameters for evaluating the degree of damage to deep-sea shallow gas reservoirs include: the rate of change in permeability, the rate of change in overall strength, and the rate of change in strength at a single point in simulated rock samples before and after drilling fluid contamination; The simulated rock sample includes skeletal particles and clay minerals; The skeletal particles include calcite and quartz sand; The calcite has a particle size of 80–200 mesh; The quartz sand includes coarse quartz sand, medium quartz sand, and fine quartz sand; The coarse quartz sand has a particle size greater than 200 mesh and not greater than 80 mesh; The particle size of the quartz sand is greater than 500 mesh and not greater than 200 mesh; The fine quartz sand has a particle size greater than 2000 mesh and not less than 500 mesh.

2. The simulation experiment method for assessing damage to shallow deep-sea gas reservoirs according to claim 1, characterized in that, The mass ratio of coarse quartz sand, medium quartz sand and fine quartz sand is 3-4:3-4:2-3; The mass ratio of calcite to quartz sand is 1-2:7-8.

3. The simulation experimental method for assessing damage to deep-sea shallow gas reservoirs according to claim 1 or 2, characterized in that, The clay minerals include montmorillonite and illite; The mass ratio of montmorillonite to illite is 1 to 2:

1.

4. The simulation experimental method for assessing damage to deep-sea shallow gas reservoirs according to claim 1 or 2, characterized in that, The mass ratio of the quartz sand to the clay minerals is 7-8:1-2.

5. The simulation experiment method for assessing damage to deep-sea shallow gas reservoirs according to claim 1, characterized in that, The method for preparing the simulated rock sample includes the following steps: The skeleton particles and clay minerals are mixed to obtain a mixture, which is then filled into a soft metal tube to obtain a rock sample soft metal tube. The rock sample soft metal tube is then soaked in simulated formation water until the water saturation of the rock sample is not less than 80% and the porosity is 30-40%.

6. The simulation experiment method for assessing damage to shallow deep-sea gas reservoirs according to claim 5, characterized in that, The filling process includes the following steps: Divide the mixture into 4 to 5 equal parts. Pour one part of the mixture into a soft metal tube and press its upper surface down to one-quarter or one-fifth of the mark with a metal rod. Let it stand. Then, gradually add the remaining 3 or 4 parts of the mixture in the same way.

7. The simulation experiment method for assessing damage to shallow deep-sea gas reservoirs according to claim 1, characterized in that, The permeability test of the simulated rock sample was conducted in accordance with the static evaluation test method for drilling fluid damage in the laboratory evaluation method for drilling fluid and completion fluid damage to the oil reservoir; in the permeability test of the simulated rock sample, the confining pressure was 2 to 2.5 MPa and the displacement pressure difference was 0.5 to 1 MPa.

8. The simulation experiment method for assessing damage to deep-sea shallow gas reservoirs according to claim 1, characterized in that, The overall strength test of the simulated rock samples involves conducting overall strength tests on simulated rock samples before and after drilling fluid contamination. The overall strength test includes the following steps: Place the simulated rock sample in the overall rock sample strength testing system, align the pointer of the pressure gauge (3) with the 0 mark, rotate the upper rotating wheel (1) to drive the pressure head (5) downward to apply force to the simulated rock sample on the support frame (4), the reading of the pressure gauge (3) pointer gradually increases until it reaches the peak value and no longer changes, stop rotating the rotating wheel (1), read the pressure peak value, the experiment ends, and substitute the pressure peak value into the strength calculation formula.

9. The simulation experiment method for assessing damage to deep-sea shallow gas reservoirs according to claim 1, characterized in that, The single-point strength test of the simulated rock sample measured the single-point penetration depth of the two end faces of the simulated rock sample before and after drilling fluid contamination, and analyzed the single-point strength of the simulated rock sample.

10. The simulation experiment method for assessing damage to deep-sea shallow gas reservoirs according to claim 1, characterized in that, The single-point penetration depth test method includes the following steps: adjust the displacement knob (7) of the top penetration test device, slowly lower the needle connecting rod (8) so that the tip of the standard needle (11) just contacts the surface of the simulated rock sample (12), conduct the experiment under the load of a standard piece (10) of 160g, and the experiment will stop automatically after 5s or 10s. Read the penetration depth of the standard needle (11) into the simulated rock sample according to the dial (9); select at least 3 points for each end face of the simulated rock sample for testing, and take the average value as the penetration depth of the corresponding end face.

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