Fractured sandstone reservoir acid fracturing transformation method based on authigenic soil acid and corollary equipment thereof

Abstract

The invention belongs to the technical field of oil and gas field development, and relates to a fractured sandstone reservoir acid fracturing transformation method based on authigenic soil acid and matched equipment thereof.The method comprises the steps that the physical property of a fractured sandstone reservoir is determined, and the applicability of an authigenic soil acid system is demonstrated in combination with an authigenic soil acid acid generation retarding mechanism and indoor authigenic soil acid experiment parameters; the effectiveness of the fractures is evaluated according to the development characteristics of the fractures, and the applicability of the acid fracturing transformation method for the fractured sandstone reservoir based on the authigenic soil acid system is demonstrated. The corollary equipment comprises a plurality of authigenic mud acid transportation tank trucks, an acid pry, a plurality of mixing tanks, a liquid supply vehicle and a plurality of fracturing pump vehicle groups, according to the method, the effective acting distance of the acid liquor is increased to 200 m from 80 m, the average open-flow capacity of a single well is increased to 450 * 10 < 4 > m < 3 > or above from 40 * 10 < 4 > m < 3 > after transformation, and the open-flow capacity is increased by 2.3 times compared with the open-flow capacity of a well with the same physical property in a block. And meanwhile, the single well productivity after transformation is high, and the flow-back rate of transformation liquid is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development, and particularly relates to an acid fracturing transformation method for fractured sandstone reservoirs based on autogenous soil acid and its supporting equipment. Background Art

[0002] Low-porosity and low-permeability fractured sandstone reservoirs are affected by the heterogeneity of fracture development. The degree of drilling fluid loss during the drilling of the target layer is different, which usually leads to serious reservoir pollution and low natural production capacity. Therefore, it is necessary to improve the single well production capacity through reservoir transformation. At the same time, according to the differences in reservoir physical properties, effective thickness, natural fracture occurrence, development density, force fracture angle, stress difference and other factors in different blocks, different transformation methods (acidizing, acid fracturing, fracture network fracturing) are adopted, and the production improvement effect varies greatly.

[0003] At present, the commonly used autogenous acid system at home and abroad is the autogenous hydrochloric acid acid solution system, which is mostly used in the acid fracturing of carbonate reservoirs. There are few reports on related research and experiments on the autogenous soil acid system; and there are very few cases of acid fracturing in fractured sandstone reservoirs at home and abroad, and the acid solution systems used are mostly conventional soil acid or organic soil acid acid solution systems. Summary of the invention

[0004] Based on this, the present invention proposes an acid fracturing reservoir transformation method for ultra-low porosity and ultra-low permeability dense fractured sandstone reservoirs. The acid system selected in this method is an autogenous soil acid system, which can achieve deep and refined transformation of the far end of the fracture; the autogenous soil acid fracturing transformation method is highly targeted, and the unobstructed flow rate of drilling is greatly improved after the transformation.

[0005] The technical solution adopted by the present invention is as follows: a method for acid fracturing transformation of fractured sandstone reservoirs based on autogenous soil acid, the method comprising the following steps: determining the physical properties of the fractured sandstone reservoir, combining the acid generation retardation mechanism of the autogenous soil acid and the indoor autogenous soil acid experimental parameters, and demonstrating the applicability of the autogenous soil acid system; evaluating the effectiveness of the fractures according to the fracture development characteristics, and demonstrating the applicability of the acid fracturing transformation method of the fractured sandstone reservoir based on the autogenous soil acid system.

[0006] Furthermore, the physical properties of the fractured sandstone reservoir are determined by: analyzing the mineral component content and clay mineral morphology based on core data from drilling, rock thin sections in rock and mineral analysis, X-ray diffraction results and scanning electron microscopy results; analyzing the pore size and characteristics based on cast thin sections; analyzing the cement characteristics based on cathodoluminescence thin sections; and analyzing the pore throat characteristics based on mercury injection curves.

[0007] Furthermore, the retarding mechanism of autogenous soil acid generation includes: retarding mechanism one: the acid-generating raw material polyformaldehyde is difficult to dissolve in water below 50°C; retarding mechanism two: the acid-generating reaction is a reversible reaction, and acid is gradually produced as the acid-rock reaction proceeds; retarding mechanism three: when the viscosity of the liquid is 50-60mPa·s, the diffusion and mass transfer rate of hydrogen ions are slowed down.

[0008] Furthermore, the indoor autogenous soil acid test parameters include: stability of the autogenous soil acid system below 50°C, acid generation rate, acid dissolution rate, compatibility and corrosion rate.

[0009] Furthermore, the effectiveness of fractures is evaluated according to the fracture development characteristics, and the applicability of the acid fracturing reconstruction method of fractured sandstone reservoirs based on the autogenous soil acid system is demonstrated, including: analyzing the fracture development characteristics based on drilling coring data, core observation and logging interpretation, evaluating the effectiveness of fractures according to the fracture development characteristics, and selecting Class I reservoirs for autogenous soil acid acid fracturing reconstruction demonstration.

[0010] Furthermore, the fracture development characteristics include fracture occurrence, development density, angle between fracture and horizontal principal stress, and vertical geostress difference.

[0011] Furthermore, the effectiveness of fractures is evaluated according to the fracture development characteristics, and the applicability of the acid fracturing reconstruction method for fractured sandstone reservoirs based on the autogenous soil acid system is demonstrated, including:

[0012] When there is no coring data from drilling, analyze the rock and mineral components and content based on the characteristics of neighboring wells and wells in the same structural position with similar geological background in neighboring blocks; analyze the relationship between rock physical properties, minimum horizontal principal stress and fracture occurrence based on the rock mechanics characteristics of the drilling well and neighboring wells; analyze the fracturability of fractures based on the in-situ stress parameters interpreted by well logging;

[0013] According to the rock and mineral composition and content, rock physical properties, the relationship between the minimum horizontal principal stress and the fracture occurrence, and the fracture fracturing ability, the fracture effectiveness is evaluated, and the Class I reservoir is selected for the demonstration of autogenous soil acid fracturing transformation.

[0014] Furthermore, the definition of Class I reservoirs is as follows: there are obvious cross fractures in imaging, the cross fracture density is greater than 0.4 per meter; the fractures are dispersed, and the standard deviation of the θ angle is greater than 25; the leakage volume is greater than 100m 3 , crack activation pressure <2.0SG.

[0015] In addition, the present invention also provides a supporting equipment, which is used to implement a method for acid fracturing transformation of fractured sandstone reservoirs based on autogenous soil acid. The supporting equipment includes multiple autogenous soil acid transport tank trucks, acid skids, multiple mixing tanks, liquid supply trucks and multiple fracturing pump truck groups; wherein, multiple autogenous soil acid transport tank trucks are connected to the acid skid, the acid skid is connected to multiple mixing tanks, the multiple mixing tanks are connected to the liquid supply truck, and the liquid supply truck is connected to multiple fracturing pump truck groups; the multiple autogenous soil acid transport tank trucks are used to separately store a variety of autogenous soil acid liquid systems composed of different single doses and transport them to the construction site; the acid skid is used to mix the various autogenous soil acid liquid systems transported by the multiple autogenous soil acid transport tank trucks; the multiple mixing tanks are used to stir the mixed various autogenous soil acid liquid systems; the liquid supply truck is used to supply the stirred various autogenous soil acid liquid systems to the multiple fracturing pump truck groups; the multiple fracturing pump truck groups are used to pump the various autogenous soil acid liquid systems into the formation wellhead.

[0016] Furthermore, the supporting equipment also includes an instrument vehicle, a balanced pump vehicle and a clean water tanker, wherein the instrument vehicle is connected to a high-temperature manifold branch, one end of the high-temperature manifold is connected to a plurality of fracturing pump vehicle groups, and the other end is connected to a formation wellhead; the balanced pump vehicle and the clean water tanker are connected to the formation wellhead in sequence; the instrument vehicle is used to display construction data in real time, issue construction instructions, and collect construction data at the same time; the balanced pump vehicle is used to balance the pressure difference between the inside and outside of the pipe string; the clean water tanker is used to provide clean water for the balanced pump vehicle.

[0017] The proposed method of acid fracturing reconstruction of fractured sandstone reservoirs based on autogenous soil acid has a slow rate of 59% compared with conventional soil acid. In addition, it has the characteristics of delayed effect and multi-stage ionization, which greatly increases the distance of acid entering the formation, and can acidify deeper, clear blockages, and better communicate remote natural fractures. This method has been successfully applied to five wells in the Kuche piedmont I and II reservoirs, increasing the effective distance of acid from 80m to 200m. After the reconstruction, the average single well open-flow rate increased from 40×10 4 m 3 Increased to 450×10 4 m 3 Compared with wells with the same physical properties in the block, the open-flow rate has increased by 2.3 times. At the same time, the single well production capacity is high after transformation, and the flowback rate of the transformation fluid is reduced.

[0018] In addition, the present invention proposes supporting equipment for realizing the above-mentioned method of acid fracturing transformation of fractured sandstone reservoirs based on autogenous soil acid. The supporting equipment can realize the separate storage and transportation of different autogenous soil acid liquids, and is equipped with a fully enclosed liquid preparation and supply system, which can meet the requirements of safe, efficient and large-volume construction.

[0019] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 Schematic diagram of the acid fracturing reconstruction method for fractured sandstone reservoirs based on autogenous soil acid;

[0022] Figure 2 It is a schematic diagram of the experimental results of low temperature stability of the autogenous soil acid system;

[0023] Figure 3 It is a schematic diagram of the experimental results of acid production rate of autogenous soil acid slow acid fracturing system;

[0024] Figure 4 It is a schematic diagram of the results of the comparison experiment on the acid dissolution rate of authigenic soil;

[0025] Figure 5 This is a schematic diagram of the first-level simulated crack morphology;

[0026] Figure 6 This is a schematic diagram of the second-level simulated crack morphology;

[0027] Figure 7 This is a schematic diagram of the production curve of Keshen 24-1 well;

[0028] Figure 8 This is a schematic diagram of the production curve of Keshen 24-6 well;

[0029] Fig. 9 This is a schematic diagram of the site layout of the authigenic soil acid construction site;

[0030] Fig.10 This is a schematic diagram of the classification and proportion of Cretaceous reservoir space types in the Kuche piedmont. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The present invention introduces an autogenous soil acid system, and comprehensively evaluates the acid performance through indoor acid acidity experiments, dynamic and static retest experiments, acid dissolution experiments, and acid corrosion fracture conductivity experiments, and applies it to the ultra-low porosity and ultra-low permeability dense fractured sandstone gas reservoir in the front of the Kuqa Mountain, and implements acid fracturing reservoir transformation.

[0033] The Cretaceous reservoir in the front of Kuche Mountain experienced two evolutionary stages: early long-term shallow burial with weak compaction, weak siliceous and strong calcareous cementation, and late rapid deep burial with strong structural compression. The diagenetic effect is the result of the superposition of the two stages. Therefore, the physical properties of the Cretaceous ultra-low porosity and ultra-low permeability fractured sandstone reservoir are controlled by the following three factors: ① Due to compaction, the physical properties of the deep buried reservoir deviate; ② Strong diagenesis, the overall deterioration of the reservoir physical properties; ③ Strong stress is also the main controlling factor of the reservoir physical properties.

[0034] Based on this, the present invention proposes an acid fracturing reconstruction method for fractured sandstone reservoirs based on autogenous soil acid. The method first starts with the petrological characteristics of the high-temperature ultra-deep well reservoir in the front of Kuqa Mountain, clarifies the main controlling factors affecting the physical properties of the reservoir, and combines the acid generation and retardation mechanism of autogenous soil acid and the results of indoor autogenous acid experimental parameters to demonstrate the applicability of the autogenous soil acid system; secondly, it deepens geological research and believes that different blocks have different fracture development characteristics. By analyzing the fracture occurrence, development density, angle between fractures and horizontal principal stress, vertical ground stress difference and other aspects, the effectiveness of the fracture is evaluated to clarify the optimal reservoir transformation process; according to the fracture development characteristics, analyze whether the autogenous acid fracturing reconstruction method is appropriate. Specifically, Figure 1 As shown, the following steps are included: determining the physical properties of the fractured sandstone reservoir, combining the autogenous soil acid generation retardation mechanism and indoor autogenous soil acid experimental parameters to demonstrate the applicability of the autogenous soil acid system; evaluating the effectiveness of the fractures according to the fracture development characteristics, and demonstrating the applicability of the acid fracturing reconstruction method for the fractured sandstone reservoir based on the autogenous soil acid system.

[0035] Specifically, determining the physical properties of fractured sandstone reservoirs includes: after a well is drilled, analyzing the mineral component content, clay mineral composition and morphological characteristics based on the core data, rock thin sections in rock and mineral analysis, X-ray diffraction (XRD) results and scanning electron microscopy (SEM) results; analyzing the pore size and characteristics based on cast thin sections; analyzing the cement characteristics based on cathodoluminescence thin sections; and analyzing the pore throat characteristics based on the mercury injection curve.

[0036] The retarding mechanism and characteristics of deep-penetrating autogenous soil acid fracturing working fluid are mainly the following three: Retarding mechanism 1: The acid-generating raw material, paraformaldehyde, is difficult to dissolve in water at room temperature (below 50°C); Retarding mechanism 2: The acid-generating reaction is a reversible reaction, and acid is gradually generated as the acid-rock reaction proceeds; Retarding mechanism 3: The viscosity of the liquid is (50-60) mPa·s, which slows down the diffusion and mass transfer rate of hydrogen ions. The chemical reaction process is as follows:

[0037] Table 1 shows the performance parameters comparison between autogenous soil acid and conventional acid.

[0038] Table 1 Performance parameters of autogenous soil acid and conventional acid

[0039]

[0040]

[0041] Indoor autogenous soil acid test parameters include: stability of the autogenous soil acid system at room temperature below 50°C, acid generation rate, acid dissolution rate, compatibility and corrosion rate. The details are as follows:

[0042] (I) Low temperature stability (theoretical concentration of autogenous soil acid is 9% HCl + 2% HF)

[0043] Through indoor experimental data comparison, such as Figure 2 As shown, when the temperature is 15°C, 24 hours after the A and B agents are mixed, the hydrochloric acid concentration is only 2.4%; 48 hours after the A and B agents are mixed, the hydrochloric acid concentration is 3.5%; when the temperature is 40°C, 24 hours after the A and B agents are mixed, the hydrochloric acid concentration is only 3.8%; 48 hours after the A and B agents are mixed, the hydrochloric acid concentration is 4.6%; the low-temperature stability of the autogenous soil acid solution can meet the requirements of on-site construction.

[0044] (II) Acid generation rate (theoretical concentration of autogenous soil acid is 9% HCl + 2% HF)

[0045] In the temperature evaluation experiment, Figure 3 As shown, Figure 3 Medium blue represents HCl concentration, and yellow represents HF concentration. When the temperature reaches 90°C, the HCl concentration reaches 6.5% and the HF concentration reaches 1.2% after two hours. The acid-generating reaction is a reversible reaction, and there is a reaction equilibrium constant. In the absence of consumption, not all the acid will be released.

[0046] (III) Retarding performance

[0047] At 90°C, self-generated soil acid (theoretical concentration 9% HCl + 2% HF) and conventional soil acid (9% HCl + 2% HF) were used to react with the silica gel sheet, respectively. Figure 4As shown in the figure, when the reaction degree reaches 85%, conventional soil acid needs 2 hours, while autogenous soil acid needs 8 hours, and the slowing performance is obvious. The final acid dissolution rate of autogenous soil acid is basically the same as that of conventional soil acid with the same concentration.

[0048] That is to say, the dissolution rate of autogenous soil acid and conventional soil acid of the same concentration is the same, but the reaction rate is different. Autogenous soil acid reacts more slowly, with a slow rate of 59% compared to conventional soil acid, which greatly increases the effective distance of the acid entering the formation, and can acidify deeper, clear blockages, and better communicate distant natural fractures.

[0049] (IV) Compatibility

[0050] The compatibility of authigenic soil acid with guar fracturing fluid, slick water, conventional soil acid, and formation water samples from the Keshen block was analyzed. The experimental plan was to conduct compatibility tests with authigenic soil acid and the other four liquids at a ratio of 1:1, 1:2, and 2:1. The experimental results show that there is a small amount of floccules when authigenic soil acid is mixed with guar fracturing fluid. Such floccules are plant guar residues, and the amount of residues is within the normal range. In the compatibility test with slick water, conventional soil acid, and standard formation water samples, no stratification, no precipitation, and no floccules were produced, indicating that authigenic soil acid is highly compatible with other mixed liquids and formation water.

[0051] (V) Corrosion rate

[0052] The corrosion test of deep penetrating autogenous soil acid solution on 13Cr steel sheet showed that when the corrosion inhibitor was added at 4.5%, it reacted with 13Cr stainless steel material at 140℃ for 4 hours, and the average corrosion rate of the three steel sheet samples was 6.76g / (m 2 h), in line with the corrosion inhibitor evaluation index requirements in SY / T5405-1996, and reaching the corrosion inhibition index of the acid system currently used in Kuche.

[0053] Specifically, if there is coring data from drilling, the fracture development characteristics are analyzed based on core observation and logging interpretation, and the fracture effectiveness is evaluated according to the fracture development characteristics, and the Class I reservoir is selected for self-generated soil acid fracturing reconstruction demonstration. The fracture development characteristics include the occurrence of fractures, development density, angle between fractures and horizontal principal stress, and vertical geostress difference.

[0054] When there is no coring data for drilling, analyze the rock and mineral components and contents according to the characteristics of adjacent wells and wells in the same structural position with similar geological background in adjacent blocks; analyze the rock physical properties, the relationship between the minimum horizontal principal stress and the occurrence of fractures according to the rock mechanics characteristics of the drilling well and the adjacent wells; analyze the fracturing ability of fractures according to the in-situ stress parameters interpreted by well logging; evaluate the effectiveness of fractures according to the rock and mineral components and contents, rock physical properties, the relationship between the minimum horizontal principal stress and the occurrence of fractures, and the fracturing ability of fractures, and select Class I reservoirs for the demonstration of autogenous soil acid fracturing.

[0055] The definition criteria for Class I reservoirs are: obvious cross fractures in imaging, with a cross fracture density greater than 0.4 per meter; fractures with dispersed orientation, with a standard deviation of theta angle greater than 25; and leakage greater than 100m 3 , crack activation pressure <2.0SG (relative density).

[0056] Taking Keshen 8-13 Well as an example, since there is no coring data in this well, the structural characteristics of the rock and mineral analysis data of the adjacent wells were used, and the frequent well leakage during the drilling of the target layer of Keshen 8-13 Well was a total of 21 leakages, including 6 loss-return leakages, with a cumulative loss density of 1.52-1.37 g / cm 3 Oil-based drilling fluid 1156.79m 3 During the logging period, it was found that oil and gas showed 20m / 8 layers, among which the section 6917-6918m showed the best, with the total hydrocarbon content increasing from 1.16% to 19.26%, and the C1 (methane) content increasing from 0.6535% to 15.1856%. The components were complete and the on-site comprehensive interpretation was poor gas layer; the logging interpretation showed that there were 28m / 10 gas layers, with an average porosity of 7.8% and an average gas saturation of 66.7%; there were 22m / 8 poor gas layers, with an average porosity of 5.0% and an average gas saturation of 61.8%; there were 24.5m / 14 dry layers.

[0057] The analysis shows that the block has a favorable structural position, and the single well drilling and testing records show that the well has good physical properties and excellent performance. The reservoir temperature of the well is high and the acid-rock reaction is fast. According to the comparison analysis of the drilling and testing records and adjacent wells, it is believed that the well is located in a structurally advantageous position, and the fracture effectiveness is good and the fracturing ability is high. In order to allow the acid to remove the near-well mud pollution and break through the far end of the fracture to achieve the purpose of deep penetration, in terms of the optimization of the main acid liquid, this well uses a deep-penetrating autogenous soil acid fracturing fluid system.

[0058] According to the characteristics of vertical physical property changes in the reservoir and the differences in the size of the vertical principal stress, combined with the main gas-producing layers, the perforated layers were selected for graded perforation transformation simulation. 46 natural fractures were identified by imaging of the target layer, with a fracture density of 0.53 fractures / m. Natural fractures were well developed, and the angles of the force fractures were large and small. Simulating the openness of natural fractures, when the bottom hole net pressure reached 1.40SG (93.8MPa), one natural fracture was opened, with an opening rate of 1%; when the bottom hole net pressure reached 1.60SG (107.2MPa), 23 natural fractures were opened, with an opening rate of 50%; when the bottom hole net pressure reached 1.72SG (115.2MPa), 46 natural fractures were opened, and all fractures were open. According to the drilling situation and ground stress data, perforation is selected, and the well sections 6893.0-6898.0m, 6901.0-6904.0m, 6914.0-6920.0m, 6925.5-6927.0m (a total of 29m / 4 sections) are divided into the first level; 6840.0-6842.5m, 6847.5-6850.5m, 6854.0-6857.0m, 6861.5-6868.0m, 6875.0-6882.0m (a total of 22m / 5 sections) are divided into the second level. The Meyer software is used for simulation. The schematic diagrams of the first-level simulated fracture morphology and the second-level simulated fracture morphology are shown as follows. Figure 5 and Figure 6 As shown, the simulation results show that the length of the first-level simulated fracture is 114m, and the length of the second-level simulated fracture is 90m, covering the reservoir of the completion and transformation section.

[0059] After completing the above-mentioned acid fracturing demonstration process of fractured sandstone reservoirs based on the autogenous soil acid system, the autogenous soil acid is stored separately and transported to the well site separately; according to its unique supporting equipment, a professional team will provide on-site services on site to ensure that the supporting equipment is fully functional, connect the main and secondary liquid supply pipelines, ensure the liquid quality and personnel safety, and ensure large-volume continuous construction. After that, the on-site acid fracturing construction and transformation will be implemented, and the spraying and drainage will be carried out to verify the acid fracturing effect of the autogenous soil acid.

[0060] Finally, after the acid fracturing construction of Keshen 8-13 well with autogenous soil acid, the single well open flow rate of Keshen 8-13 well increased from 16×10 4 m 3 / d increased to 554×10 4 m 3 / d, the unobstructed flow rate is further improved.

[0061] In addition, the present invention also verifies the reservoir transformation effect on Keshen Block 8 and Keshen Block 24, and the analysis results are as follows:

[0062] (1) The unobstructed flow rate of autogenous soil acid fracturing transformation has been greatly improved.

[0063] The target layer of Keshen 8-2T Well was lost during drilling. The total loss of drilling fluid with a relative density of 1.50 was 602.3m 3 Before the transformation, the oil nozzle was 5mm, the oil pressure was 60.3MPa, and the daily gas output was 24.8×10 4 m 3 The calculated unimpeded flow rate is 64.5×10 4 m 3 / d; through the acid fracturing transformation of autogenous soil, 8mm oil nozzle, oil pressure 66.405MPa, daily gas production 62.02×10 4 m 3 The calculated unimpeded flow rate is 457.9×10 4 m 3 / d. The single well productivity has been improved, and the unimpeded flow rate has increased by 6 times.

[0064] The autogenous acid fracturing technology was successfully applied in three wells in the Class I and II reservoirs of Keshen 8 and Keshen 24 blocks. After the fracturing, the average single well open flow rate increased from 40×10 4 m 3 / d increased to 450×10 4 m 3 / d or more, the open-flow rate is increased by 2.3 times compared with wells with the same physical properties in the block.

[0065] (2) When the formation pore pressure decreases, the unimpeded flow rate can reach the block average.

[0066] The average open-flow rate of a single well in the Keshen 8 gas reservoir at the initial stage of development was 454.6×10 4 m 3 After several years of mining, the formation pore pressure dropped from 122MPa in the early stage of development to 82MPa. The calculated open-flow rate of Keshen 8-2T well after acid fracturing with autogenous soil acid was 457.9×10 4 m 3 , the calculated open-flow rate of Keshen 8-13 well is 530×10 4 m 3 After the transformation, the average open-flow rate of the two wells was 494×10 4 m 3 In the case of decreasing pore pressure, the open-flow rate of the above two wells after acid fracturing with autogenous soil acid can still reach the average value of the block, which fully demonstrates that the autogenous soil acid fracturing has a good effect (see Table 2).

[0067] (3) In the process of seeking production, the production system expanded, and while output increased, pressure increased instead of decreased.

[0068] like Fig.10The figure shows the division of reservoir space types and their proportions in the Cretaceous system in the front of Kuche Mountain. It can be seen from the figure that the reservoir space of the sandstone reservoir in the front of Kuche Mountain is composed of pores, throats and fractures, which often appear as dual seepage channels of porous media. Pores also include primary intergranular pores and dissolution-enlarged pores. In the process of oil and gas seeping from low-porosity and low-permeability reservoirs into fractures and then converging from fractures to oil and gas wellbores to form oil and gas flows, the fluid flow pattern has evolved from seepage to pipe flow. This normal flow pattern change will cause the oil and gas pressure to drop while the production increases.

[0069] The wells in the Keshen 24 block that have been transformed by sand fracturing and conventional soil acid have a production curve showing that as the working system increases, the production increases significantly, but the wellhead pressure shows a clear downward step. For example, the production curve of the Keshen 24-1 well is as follows: Figure 7 As shown in the figure, it indicates that the energy of natural gas flowing from the reservoir space to the fracture channel is insufficient, or the fracture network system is not fully connected. In the process of deep penetration acid rock reaction by delayed acid fracturing with autogenous soil acid in Keshen 24-6 well, the deep reservoir was fully activated and mobilized, such as Figure 8 The production curve shown shows that as the production system expands, the pressure increases instead of decreases while the output increases.

[0070] At the same time, the shut-in pressure of Keshen 24-6 was 75.868MPa, the oil pressure of 6mm nozzle was 75.028MPa, and the pressure difference was 0.84MPa; the shut-in pressure of Keshen 24-1 was 84.982MPa, the oil pressure of 6mm nozzle was 81.696MPa, and the pressure difference was 3.28MPa. Compared with the same working system, the production pressure difference of Keshen 24-6 well is smaller, the communication is better, and the skin coefficient is lower. During the process of drainage, the nozzle becomes larger and the output increases, but the oil pressure does not drop. The deep oil and gas in the formation are communicated and released, giving full play to the deep penetration characteristics of the autogenous soil acid.

[0071] (IV) After autogenous acid transformation, the single well production capacity is high and the transformation fluid return rate is low.

[0072] According to the capillary pressure principle of oil and gas reservoirs, reservoir reconstruction construction for reservoirs with poor reservoir properties is characterized by high construction pressure, poor formation permeability, and no liquid inflow. On the other hand, during the flowback process, the liquid that has not entered the deep formation will basically flow back along the channel, so the flowback rate of low-porosity and low-permeability matrix sandstone reservoirs will be high. On the contrary, due to the development of fractures in fractured sandstone reservoirs, the reservoirs show high permeability characteristics, and the construction process is characterized by low construction pressure, and liquid can easily enter the formation. At the same time, the flowback rate during the flowback process is relatively low.

[0073] By analyzing the statistics of reservoir reconstruction construction parameters and flowback rate in Keshen 8 block (see Table 2), despite the use of different reconstruction methods, the overall characteristics are that wells with good reservoir properties or developed fractures have high single well production capacity and low flowback rate after reservoir reconstruction; wells with poor reservoir properties and relatively undeveloped fractures have low single well production capacity and high flowback rate. For example, in the table, Keshen 8-9, Keshen 8003 and Keshen 8-11 wells, the number of fractures in the reconstruction section is less than 30, and the physical property deviations explained by well logging, the single well production capacity is low after reconstruction, and the flowback rate is high, close to 50%. However, Well Keshen 8-1 and Well Keshen 8-4, which were acid-fractured with fracture networks, Well Keshen 8-3, which was unblocked by barite, and Well Keshen 8-2T and Well Keshen 8-13, which were acid-fractured with autogenous soil acid, generally experienced drilling fluid loss during the drilling process, with the loss volume reaching hundreds of cubic meters. Cracks were widely developed, with a high density of fracture lines. At the same time, the flowback rate did not exceed 15%, and the flowback rate of two wells did not exceed 10%.

[0074] The Keshen 24 block also has similar characteristics (see Table 3). The open-flow rates of the Keshen 24-5 well after acid fracturing and the Keshen 241-4 well after sand fracturing were 44.2×10 4 m 3 / d and 66×10 4 m 3 / d, the physical properties are poor and the production is low, and the flowback rates are 56.7% and 61.17%, respectively, both exceeding 50%. The open-flow rates of Keshen 243, Keshen 24-1, Keshen 242 after fracture network acid fracturing and Keshen 24-6 after autogenous soil acid fracturing are 251.0×10 4 m 3 / d,228.0×10 4 m 3 / d,439.0×10 4 m 3 / d and 418.2×10 4 m 3 / d, the single well production capacities were relatively high, and the flowback rates were 14.96%, 31.66%, 30.10% and 12.25% respectively.

[0075] Based on the application of autogenous soil acid in the ultra-low porosity and ultra-low permeability fractured sandstone reservoir in the front of Kuche Mountain, the following conclusions are summarized: The autogenous soil acid system was tested in the clastic rock reservoir in the front of Kuche Mountain for the first time in 2020. The open-flow rate of Keshen 8-2T well was increased from 64.5×10 4 m 3 / d increased to 458×10 4 m 3 / d; the unimpeded flow rate of Keshen 24-6 well increased from 45.7×10 4 m 3 / d increased to 418×104 m 3 / d, and the open-flow rates of the two wells increased by 6.1 times and 8.1 times respectively. In 2021, the autogenous soil acid system was promoted and applied in three wells, namely Keshen 8-13, Keshen 8-17 and Bozi 3-K2 wells, with significant implementation effects. The open-flow rate of Keshen 8-13 well increased from 16×10 4 m 3 / d increased to 554×10 4 m 3 / d, and the open-flow rate was further improved. After the transformation of Keshen 8-17 well and Bozi 3-K2 well, the open-flow rate also reached 337.5×10 4 m 3 / d and 325.3×10 4 m 3 / d. The autogenous soil acid system has been successfully applied in five wells in the Kuche piedmont I and II reservoirs, increasing the effective action distance of the acid from 80m to 200m. After the transformation, the average single well open flow rate increased from 40×10 4 m 3 Increased to 450×10 4 m 3 Compared with wells with the same physical properties in the block, the unobstructed flow rate has increased by 2.3 times, forming a delayed acid fracturing transformation technology for ultra-deep, high-temperature and high-pressure wells in the Kuche piedmont.

[0076] Table 2 Statistical data of reservoir transformation effect in Keshen 8 block

[0077]

[0078] Table 3 Statistical data of reservoir transformation effect in Keshen 24 block

[0079]

[0080] Finally, combined with the performance parameter characteristics of autogenous soil acid, and taking advantage of its advantages in delayed acid fracturing mechanism, transportation, preparation and construction, a set of supporting equipment for acid fracturing transformation of fractured sandstone reservoirs based on autogenous soil acid to improve single well production capacity is formed. Fig. 9 As shown in the figure, the two types of autogenous soil acid systems composed of two single agents A and B in the supporting equipment are stored separately and transported to the construction site. During the construction process, the autogenous soil acid is not mixed in advance; instead, it is prepared and used immediately to ensure that the acid is generated slowly and enters the formation to further acid erode, thus achieving the construction effect. Then, the acid skid equipment (theoretical displacement of the acid skid is 12m 3 / minute, which can meet the needs of large-volume construction on site, and sufficient liquid supply) connect the autogenous soil acid A and B single agents, mix them once when the acid pry is sucked in, and pour them into the mixing tank for stirring. By measuring the liquid level in the tank, ensure that the mixing ratio of A and B two single agents is A: B = 1: 1, and mix them thoroughly after stirring in the mixing tank. There are 2 mixing tanks on site, each with a capacity of 50m 3 , two 100m 3 , the tank has sufficient liquid and the tank body has sufficient water supply valves. During construction, 10 water supply pipelines can be connected to meet the construction displacement of 8 cubic meters / minute. After the A and B agents are mixed in the mixing tank, the autogenous soil acid and fracturing fluid are supplied to the fracturing pump truck through the liquid supply truck, and then pumped into the formation wellhead through the high-pressure manifold through the fracturing pump truck. During the pumping process, the autogenous soil acid begins to heat up, and when the temperature reaches 80°C, it begins to generate acid. Unlike conventional thickening acid, the conventional thickening acid itself has an acid concentration of 20%. After entering the formation, 20% of H + Reacting with the formation rock, the reaction distance is limited, and after the autogenous acid enters the formation, H + From nothing to something, H is generated + At the same time, it reacts with the rock to extend the etching distance. At the same time, the autogenous soil acid itself has a certain viscosity, and the liquid is a suspended particle emulsion. After entering the formation, the filtration loss is low. It can be used as a pre-fracturing fluid to extend the length of the fracture, which is conducive to communicating with the caves in the reservoir or activating the remote natural fractures. The high-pressure manifold is also connected to the instrument vehicle, which is used to develop construction instructions, display construction data in real time, and collect construction data to provide support for subsequent analysis; the wellhead is also connected to a balanced pump truck and a clean water tank truck. The balanced pump truck is used to balance the pressure difference between the inside and outside of the pipe string to ensure the safety of the pipe string and tools in the well; the clean water tank truck is used to provide clean water for the balanced pump truck.

[0081] The slow rate of autogenous acid generation is mainly due to the fact that it takes time for the paraformaldehyde in the raw material to hydrolyze. It takes 80 minutes to completely hydrolyze in a 90°C water bath. + , is a reversible reaction, H + The concentration of H affects the reaction rate. + Reacts with rocks, promoting the positive reaction to continue and continuously generating acid until H + Complete release; the autogenous acid itself has a certain viscosity. The viscosity of the mixed solution after acid generation is 60mpa·s, which can delay H + The diffusion and mass transfer of the oil and gas will be improved. Finally, the acid-rock reaction rate will be reduced, the acid fracturing effect will be achieved, and the single well production capacity will be increased.

[0082] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for acid fracturing of fractured sandstone reservoirs based on autogenous soil acid, characterized in that: The method comprises the following steps: Determine the physical properties of fractured sandstone reservoirs, combine the slow-generation mechanism of autogenous soil acid and the experimental parameters of indoor autogenous soil acid, and demonstrate the applicability of the autogenous soil acid system; The effectiveness of fractures was evaluated according to the fracture development characteristics, and the applicability of the acid fracturing reconstruction method for fractured sandstone reservoirs based on the autogenous soil acid system was demonstrated.

2. The method according to claim 1, characterized in that Determination of the physical properties of fractured sandstone reservoirs includes: Based on the core data of drilling, rock thin sections in rock and mineral analysis, X-ray diffraction results and scanning electron microscopy results, the mineral component content and clay mineral morphological characteristics are analyzed; the pore size and characteristics are analyzed based on the casting thin sections; the cement characteristics are analyzed based on the cathode luminescence thin sections; and the pore throat characteristics are analyzed based on the mercury injection curve.

3. The method according to claim 2, characterized in that The mechanism of autogenous soil acid generation retardation includes: Slowing mechanism 1: The acid-generating raw material, paraformaldehyde, is difficult to dissolve in water below 50°C; Slowing mechanism 2: The acid-generating reaction is a reversible reaction, and acid is gradually generated as the acid-rock reaction proceeds; Retarding mechanism three: When the viscosity of the liquid is 50-60 mPa·s, the diffusion and mass transfer rate of hydrogen ions are slowed down.

4. The method according to claim 3, characterized in that The indoor autogenous soil acid test parameters include: stability of the autogenous soil acid system below 50°C, acid generation rate, acid dissolution rate, compatibility and corrosion rate.

5. The method according to claim 1, characterized in that The effectiveness of fractures is evaluated according to the fracture development characteristics, and the applicability of the acid fracturing reconstruction method for fractured sandstone reservoirs based on the autogenous soil acid system is demonstrated, including: The fracture development characteristics were analyzed based on the drilling coring data, core observation and logging interpretation, and the fracture effectiveness was evaluated according to the fracture development characteristics. The Class I reservoir was selected for the demonstration of autogenous soil acid fracturing transformation.

6. The method according to claim 5, characterized in that The characteristics of fracture development include fracture occurrence, development density, angle between fracture and horizontal principal stress, and vertical geostress difference.

7. The method according to claim 1, characterized in that The effectiveness of fractures is evaluated according to the fracture development characteristics, and the applicability of the acid fracturing reconstruction method for fractured sandstone reservoirs based on the autogenous soil acid system is demonstrated, including: When there is no coring data from drilling, analyze the rock and mineral components and content based on the characteristics of neighboring wells and wells in the same structural position with similar geological background in neighboring blocks; analyze the relationship between rock physical properties, minimum horizontal principal stress and fracture occurrence based on the rock mechanics characteristics of the drilling well and neighboring wells; analyze the fracturability of fractures based on the in-situ stress parameters interpreted by well logging; According to the rock and mineral composition and content, rock physical properties, the relationship between the minimum horizontal principal stress and the fracture occurrence, and the fracture fracturing ability, the fracture effectiveness is evaluated, and the Class I reservoir is selected for the demonstration of autogenous soil acid fracturing transformation.

8. The method according to claim 6 or 7, characterized in that: Class I reservoirs are defined as: having obvious cross fractures in imaging, with a cross fracture density greater than 0.4 per meter; fractures with dispersed orientation, with a standard deviation of theta angle greater than 25; and leakage greater than 100m 3 , crack activation pressure <2.0SG.

9. A supporting device, which is used to implement the method for acid fracturing of fractured sandstone reservoirs based on autogenous soil acid according to any one of claims 1 to 8, characterized in that: The supporting equipment includes multiple self-generated soil acid transport tank trucks, acid skids, multiple mixing tanks, fluid supply trucks and multiple fracturing pump truck groups; A plurality of autogenous soil acid transport tank trucks are connected to the acid skid, the acid skid is connected to a plurality of mixing tanks, the plurality of mixing tanks are connected to a fluid supply truck, and the fluid supply truck is connected to a plurality of fracturing pump truck groups; The multiple autogenous soil acid transport tankers are used to store multiple autogenous soil acid liquid systems with different single-dose compositions separately and transport them to the construction site; The acid skid is used to mix a plurality of autogenous soil acid liquid systems transported by a plurality of autogenous soil acid transport tankers; The multiple mixing tanks are used to stir the mixed multiple autogenous soil acid solution systems; The liquid supply vehicle is used to supply the stirred multiple autogenous soil acid liquid systems to multiple fracturing pump vehicle groups; The multiple fracturing pump truck groups are used to pump multiple autogenous soil acid fluid systems into the formation wellhead.

10. The supporting equipment according to claim 9, characterized in that: The supporting equipment also includes an instrument vehicle, a balanced pump vehicle and a clean water tanker, among which: The instrument vehicle is connected to the high-temperature manifold branch, one end of the high-temperature manifold is connected to multiple fracturing pump trucks, and the other end is connected to the formation wellhead; the balance pump truck and the clean water tank truck are connected to the formation wellhead in turn; The instrument vehicle is used to develop construction instructions, display construction data in real time, and collect construction data; The balanced pump truck is used to balance the pressure difference between the inside and outside of the pipe string; The clean water tanker is used to provide clean water for the balancing pump truck.

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