A method for sandstone reservoir plugging and increasing irrigation of geothermal well

Abstract

The present application relates to a kind of sandstone reservoir plugging for geothermal well, belongs to the field of geothermal resource development and utilization.The method comprises: (1) obtaining recharge reservoir data, including reservoir permeability and reservoir mineral composition, reservoir average permeability is less than or equal to 300mD for middle-low permeable layer, and reservoir average permeability is greater than 300mD for middle-high permeable layer;(2) according to the reservoir permeability selection plugging solution, the plugging solution for middle-low permeable layer is base plugging solution, and the plugging solution for middle-high permeable layer is composed of base plugging solution and long-acting stable liquid;(3) according to the reservoir mineral composition selection base plugging solution;(4) according to the result of step (2), (3), plugging solution is prepared;(5) plugging solution is injected alone or injected with recharge water in formation during production process.The present application can effectively plug middle, shallow sandstone geothermal recharge well, and can achieve low corrosion, no backflow, anti-collapse, long-term deep reconstruction.

Description

Technical Field

[0001] This invention belongs to the field of geothermal resource development and utilization, and specifically relates to a method for unblocking and increasing the injection period of sandstone geothermal wells. Background Technology

[0002] With the increasing urgency of energy structure adjustment and air pollution control in my country, geothermal energy, as a clean and renewable energy source with great potential, will play an increasingly important role. The guiding principle for geothermal development in my country is "extracting heat but not water," using clean energy for heating. Artificial reinjection is an inevitable way to achieve the sustainable recycling of geothermal energy and water resources, but blockage is a bottleneck problem restricting reinjection. How to unblock and extend the effective period of unblocking is an effective measure to achieve "extracting heat but not water." To improve the reinjection efficiency of reinjection wells, researchers have conducted a large amount of related research (Zhou Xin. Research on the Blockage Mechanism of Porous Groundwater Reinjection in Sedimentary Basins—Taking the Xi'an Sanqiao Geothermal Tailwater Reinjection Well as an Example [D]. Chang'an University; Kang Han, Wang Mouwei, Pan Jun, et al. The Influence of pH on Biological Blockage of Groundwater Source Heat Pump Reinjection Wells [J]. Journal of Shenyang Jianzhu University: Natural Science Edition, 2021; Chang Ming. Analysis of the Causes and Solutions to the Reduced Reinjection Effect of Geothermal Reinjection Wells [J]. Petrochemical Technology, 2016).

[0003] "A pressureless geothermal reinjection system and reinjection method" (CN202011344167.1) uses a nitrogen compensation device to adjust the injection pressure and maintain the steady-state operation of the reinjection system; "A new reinjection method to improve the reinjection efficiency of medium-deep sandstone geothermal systems" (CN202110970093.0) uses digital simulation to adjust and optimize reinjection parameters to obtain reinjection injection parameters that improve reinjection efficiency; "A device and method for unblocking sandstone geothermal wells based on gas-liquid mixtures" (CN202110769698.3) cleans reinjection water physically to improve reinjection efficiency; "A chemical method for treating microbial blockage during artificial reinjection" (CN201910005295.4) uses an oxidant to sterilize the injected water and reduce bacterial damage and blockage of the reinjection well; "A method to improve the production and injection efficiency of hydrothermal geothermal well groups" (CN202210103485.1) uses shallow water reinjection to ensure sufficient production well capacity.

[0004] Current research on unclogging reinjection wells mostly focuses on improving the injection effect of reinjection wells through processes and equipment, but lacks relevant research on how to unclogging reinjection wells.

[0005] This invention proposes a novel method for unblocking and enhancing the injection of sandstone reservoirs. Based on the damage characteristics of reinjection wells and feasible unblocking techniques, it can effectively improve the reinjection period and reservoir stimulation efficiency of sandstone geothermal wells. Summary of the Invention

[0006] The purpose of this invention is to provide a method for unblocking and reinjecting sandstone reservoirs in geothermal wells. This method is reliable in principle and easy to operate. Based on a clear understanding of the blockage mechanism of geothermal well reinjection, it can effectively unblock medium and shallow sandstone geothermal reinjection wells while achieving deep modification with low corrosion, no backflow, no collapse, and long effective period. This is of great significance for realizing the sustainable recycling of geothermal energy and water resources.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solution.

[0008] A method for unblocking and enhancing the injection of sandstone reservoirs in geothermal wells includes the following steps:

[0009] (1) Obtain reinjection reservoir data, including reservoir permeability and reservoir mineral composition.

[0010] A reservoir with an average permeability of less than or equal to 300 mD is classified as a low to medium permeability reservoir, while a reservoir with an average permeability of greater than 300 mD is classified as a medium to high permeability reservoir.

[0011] The hydrochloric acid soluble content in reservoir minerals is categorized as follows: less than or equal to 10%; greater than 10% and less than or equal to 15%; and greater than 15% and less than or equal to 30%. The hydrochloric acid soluble content is obtained using hydrochloric acid dissolution experiments (contents exceeding 30% are not applicable in this invention).

[0012] The clay content in reservoir minerals was categorized into three groups: less than or equal to 5%; greater than 5% and less than or equal to 10%; and greater than 10%. The clay mineral content was obtained using XRD data analysis.

[0013] (2) Select unblocking fluid based on reservoir permeability

[0014] Medium to low permeability layer, unblocking fluid is the base unblocking fluid.

[0015] The medium-to-high permeability layer is unblocked by a solution consisting of a basic unblocking solution and a long-lasting stabilizing solution.

[0016] The basic unblocking solution is composed of the following components by weight: 20-70 parts acid, 5-20 parts chelating agent, 1-5 parts corrosion inhibitor, 1-5 parts clay stabilizer, totaling 100 parts, with the remainder being water.

[0017] The long-lasting stabilizing liquid is composed of the following components in parts by weight: 5-30 parts stabilizer, 5-30 parts alcohol, 1-5 parts emulsifier, and 0.5-5 parts dispersant.

[0018] The acid solution is composed of a basic acid and a fluorinated acid or salt. The basic acid is one or more of hydrochloric acid, phosphoric acid, formic acid, acetic acid, oxalic acid, citric acid, formaldehyde, ammonium chloride, and aminosulfonic acid. The fluorinated acid or salt is one or more of hydrofluoric acid, fluoroboric acid, and ammonium fluoride.

[0019] The chelating agent is one or more of EDTA, EDTA.2Na, EDTA.4Na, DTPA, HEDTA, NTA, EGTA, ATMP, HEDP, EDTMP, DTPMP, ATP, and HPMA.

[0020] The corrosion inhibitor is one or more of the following: thiol, polyethylene glycol ether, sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, diethylenetriamine, hexamethylenetetramine, butynediol, butynediol, imidazoline oleate, 4-methylpyridine, and 4-vinylpyridine.

[0021] The clay stabilizer is one or more of 2,3-epoxypropyltrimethylammonium chloride, γ-aminopropyltriethoxysilane, polydimethyldiallylammonium chloride, hexadecyltrimethylammonium chloride, and hexadecylbenzyldimethylammonium chloride.

[0022] The stabilizer is one or more of tetraethyl orthosilicate, trimethylethoxysilane, n-octyltriethoxysilane, cyclomethylcyclosiloxane, decamethylcyclopentasiloxane, and polytrifluoropropylmethylsiloxane.

[0023] The alcohol is one or more of ethanol, methanol, propanol, and ethylene glycol.

[0024] The emulsifier is composed of commonly used O / W emulsifiers and W / O emulsifiers in a 1:1 mass ratio. O / W emulsifiers include one or more of dodecylphenol polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, nonionic paraffin microemulsifier NMP, cationic paraffin microemulsifier CMP, Tween 20, Tween 40, Tween 60, and Tween 80; W / O emulsifiers include one or more of Span 20, Span 40, Span 60, and Span 80.

[0025] The dispersant is one or more of sodium oleate, fatty alcohol sulfate salt, sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, octadecyleneamine acetate, aminopropylamine dioleate, polyethylene glycol, and sodium tripolyphosphate.

[0026] All of the above substances are commercially available.

[0027] (3) Select basic unblocking fluid based on reservoir mineral composition

[0028] The amount of acid solution used is determined based on the content of hydrochloric acid-soluble matter in the reservoir minerals. For hydrochloric acid-soluble matter content less than or equal to 10%, the amount of acid solution used is 20-40 parts; for hydrochloric acid-soluble matter content greater than 10% but less than or equal to 15%, the amount of acid solution used is 40-50 parts; and for hydrochloric acid-soluble matter content greater than 15%, the amount of acid solution used is 50-70 parts.

[0029] The acid composition, i.e., the ratio of basic acid to fluoride or salt, is determined based on the clay content in the reservoir minerals. For clay content less than or equal to 5%, fluoride or salt constitutes 0-15% of the total acid content; for clay content greater than 5% but less than or equal to 10%, fluoride or salt constitutes 15-30% of the total acid content; and for clay content greater than 10%, fluoride or salt constitutes 30-45% of the total acid content.

[0030] (4) Preparation of unblocking fluid

[0031] For medium- and low-permeability layers, the unblocking solution is prepared as follows: add acid to water and stir until homogeneous, then add chelating agent, corrosion inhibitor, and clay stabilizer and stir until homogeneous.

[0032] For medium-to-high permeability layers, the unblocking solution preparation process is as follows: Divide the alcohol into two portions of 30% and 70%, and the water into two portions of 30% and 70%. Mix the stabilizer, 30% alcohol, and W / O emulsifier evenly to prepare liquid A. Mix the chelating agent and 30% water evenly to prepare liquid B. Add liquid B to liquid A and stir evenly to form emulsion C. Gradually add the acid, 70% water, 70% alcohol, corrosion inhibitor, clay stabilizer, O / W emulsifier, and dispersant in sequence and stir evenly to prepare liquid D. Finally, slowly add emulsion C to liquid D and stir at low speed until evenly mixed.

[0033] (5) Inject the unblocking fluid separately or inject it into the formation during the production process along with the reinjection water.

[0034] Separate injection: First, dilute the unblocking fluid with surface water to 1-3 times (by volume), then inject it into the formation, shut in the well for 1-3 hours, and resume normal production.

[0035] Production process injection: The ratio of unblocking fluid to reinjection water is 1:1 to 1:5 (volume ratio). A tee is installed at the wellhead to inject the unblocking fluid and reinjection water into the formation simultaneously, without interrupting production during the unblocking process.

[0036] The underground hot water from geothermal wells is extracted for thermal energy utilization, and the utilized water needs to be reinjected into the formation. Due to the changes in temperature and pressure during the surface process, the composition and mineralization of the water have changed. This water that has released thermal energy is called reinjection water.

[0037] Geothermal wells are typically used for heating only for half the year, so the reinjection period is also only six months. The wells are shut off for the rest of the year, and surface water is used for dilution during unblocking. To improve the unblocking effect during production, reinjection can be stopped first, unblocking can be performed directly, and then production can be resumed.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) Since conventional unblocking construction procedures are complicated and there are currently no unblocking measures for reinjection wells, the method described in this invention effectively solves the problems of difficult injection and short unblocking period in geothermal reinjection wells;

[0040] (2) This invention overcomes the shortcomings of previous designs that only focused on the physical and chemical properties of unblocking materials. It combines reservoir characteristics to formulate a solution, establishes a connection between the unblocking system and reservoir characteristics, and selects an appropriate unblocking system according to the unblocking requirements of reservoirs with different characteristics. It can systematically and efficiently improve the unblocking effect of reinjection wells and has broad application prospects.

[0041] (3) Since most of the reinjection wells are high-permeability, loose sandstone reservoirs, the present invention uses a stabilizer in the unblocking fluid to stabilize the near-wellbore area while unblocking, which can prevent near-wellbore collapse and improve the unblocking effect.

[0042] (4) In the unblocking fluid system, the unblocking material is encapsulated by the stabilizer, which stabilizes the formation and slowly releases the unblocking material within the rock skeleton, thereby achieving long-term unblocking and further reducing the rate of scale formation in the reinjected water after unblocking, thus extending the unblocking cycle.

[0043] (5) The present invention combines unblocking, consolidation and slow release in a coordinated manner, which not only achieves unblocking and near-well stability, but also achieves long-term unblocking. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and examples to enable those skilled in the art to understand the invention. However, it should be understood that the present invention is not limited to the specific embodiments described herein. For those skilled in the art, any variations that fall within the spirit and scope of the invention as defined and determined by the appended claims are all within the scope of protection. Example

[0045] Taking the H-1 reinjection well as the case study, which was completed in 2018, the reinjection section is a sandstone reservoir, ranging from 2438 to 3573 meters in length, with a thickness of 1135 meters. The porosity ranges from 5.6% to 30.4%, averaging 23.6%; the permeability ranges from 74.9 to 1432.2 mD, averaging 856 mD. The geothermal chemistry is sodium sulfate-bicarbonate type. The mineralization is 3768 mg / L, dissolved solids are 3200 mg / L, total hardness (calculated as calcium carbonate) is 85.1 mg / L, pH is 8.61, classifying it as weakly alkaline and extremely soft water, with a total hardness of 40 mg / L. In 2022, compared to 2018, the well's reinjection capacity was reduced by approximately 45%.

[0046]

[0047] (1) Obtain reinjection reservoir data, including reservoir permeability and reservoir mineral composition.

[0048] The H-1 reinjection well has an average reservoir permeability of 856 mD, with layers greater than 300 mD classified as medium to high permeability.

[0049] To test the hydrochloric acid soluble content in reservoir minerals, 10g of rock sample was taken, 100ml of acid (12% HCl) was added, and the acid reaction was carried out for 4 hours. The hydrochloric acid soluble content was calculated by measuring the weight loss of the rock sample. Three parallel samples were tested, and the values ​​were 11.25%, 11.63%, and 11.56%, respectively, falling between 10% and 15%.

[0050] The reservoir rock samples were ground into 200-mesh powder and subjected to XRD analysis. Three parallel samples were tested, and the clay content in the reservoir minerals was 6.3%, 7.1%, and 6.6%, respectively, ranging from 5% to 10%.

[0051] (2) Select unblocking fluid based on reservoir permeability

[0052] The H-1 reinjection well reservoir is a medium-to-high permeability layer, and the unblocking fluid consists of a basic unblocking fluid and a long-lasting stabilizing fluid.

[0053] Long-lasting stabilizing solution:

[0054] 30 parts stabilizer: tetraethyl orthosilicate;

[0055] 10 parts alcohol: ethanol;

[0056] 2 parts emulsifier: 1 part alkylphenol polyoxyethylene ether (O / W), 1 part Span 60 (W / O);

[0057] 2 parts dispersant: 1 part sodium dodecyl sulfonate, 1 part sodium tripolyphosphate.

[0058] (3) Select basic unblocking fluid based on reservoir mineral composition

[0059] Basic unblocking solution: 50 parts acid, 10 parts chelating agent, 5 parts corrosion inhibitor, 5 parts clay stabilizer, and 30 parts water.

[0060] 50 parts acid solution: 5 parts hydrochloric acid, 10 parts aminosulfonic acid, 20 parts acetic acid, and 15 parts ammonium fluoride.

[0061] 10 parts chelating agent: 4 parts EDTA.2Na, 3 parts DTPA, 3 parts HEDP.

[0062] 5 parts corrosion inhibitor: imidazoline oleate.

[0063] Five parts of the clay stabilizer were: polydimethyldiallyl ammonium chloride.

[0064] (4) Preparation of unblocking solution I

[0065] For medium- to high-permeability layers, first prepare all materials according to the specified ratio.

[0066] Including: ethanol, water, tetraethyl orthosilicate, alkylphenol polyoxyethylene ether (O / W), EDTA.2Na, DTPA, HEDP, hydrochloric acid, aminosulfonic acid, acetic acid, ammonium fluoride, imidazoline oleate, polydimethyldiallylammonium chloride, Span 60 (W / O), sodium dodecyl sulfonate, and sodium tripolyphosphate.

[0067] Divide the ethanol into two portions of 30% and 70%. Divide the water into two portions of 30% and 70%.

[0068] Liquid A1 was prepared by mixing tetraethyl orthosilicate, 30% ethanol, and Span 60 (W / O) until homogeneous.

[0069] Liquid B1 was prepared by mixing EDTA·2Na, DTPA, HEDP, and 30% water until homogeneous.

[0070] Add liquid B1 to liquid A1 and stir until well mixed to form emulsion C1.

[0071] Hydrochloric acid, aminosulfonic acid, acetic acid, ammonium fluoride, 70% water, 70% ethanol, oleic acid imidazoline, polydimethyldiallyl ammonium chloride, alkylphenol polyoxyethylene ether (O / W), sodium dodecyl sulfonate, and sodium tripolyphosphate are added to prepare liquid D1 in sequence and stirred until homogeneous.

[0072] Finally, emulsion C1 is slowly added to liquid D1 and stirred at low speed until homogeneous to prepare unblocking solution I.

[0073] (5) Using the method of injecting water back into the formation to unblock the blockage

[0074] Unblocking fluid is injected into the formation during the production process: The ratio of unblocking fluid I to reinjection water is 1:2 to 1:3 (volume ratio). A tee is installed at the wellhead to inject the unblocking fluid and reinjection water into the formation simultaneously, without interrupting production during the unblocking process. Example

[0075] The H-2 reinjection well was used as the subject of this study. Completed in 2019, the main reinjection section is from 1540.18 to 2724.65 m in length and from 1430.08 to 2585.35 m in vertical depth. The geothermal chemistry is sodium bicarbonate chloride type water (HCO3.Cl-Na). The salinity is 2002 mg / L, classifying it as slightly brackish water; dissolved solids are 1636 mg / L; total hardness (calculated as calcium carbonate) is 25.0 mg / L, classifying it as very soft water; pH is 8.16, classifying it as weakly alkaline water. The formation thickness is 1155.27 m. The maximum porosity is 32.87%, the minimum is 13.94%, and the average is 23.74%. The maximum permeability is 1324.28 mD, the minimum is 6.14 mD, and the average is 262.57 mD. The maximum mud content is 40.96%, the minimum is 0.54%, and the average is 14.80%. The maximum sand layer thickness is 8.9m, the minimum is 1.0m, and the average sand layer thickness is 3.2m.

[0076] In 2022, compared to 2019, the well's reinjection capacity was damaged by approximately 67%.

[0077]

[0078] (1) Obtain reinjection reservoir data, including reservoir permeability and reservoir mineral composition.

[0079] The average permeability of the H-2 reinjection well reservoir is 262.57 mD, and layers with permeability less than 300 mD are classified as medium to low permeability.

[0080] To test the hydrochloric acid soluble content in reservoir minerals, 10g of rock sample was taken, 100ml of acid (12% HCl) was added, and the reaction was carried out for 4 hours. The weight loss of the rock sample was then used to calculate the hydrochloric acid soluble content. Three parallel samples were tested, and the values ​​were 6.58%, 6.32%, and 6.86%, respectively. The hydrochloric acid soluble content was less than 10%.

[0081] The reservoir rock samples were ground into 200-mesh powder and subjected to XRD analysis. Three parallel samples were tested, with concentrations of 12.72%, 11.95%, and 13.16%. The clay mineral content was greater than 10%.

[0082] (2) Select unblocking fluid based on reservoir permeability

[0083] The H-2 reinjection well reservoir is a medium-low permeability layer, and the unblocking fluid is the basic unblocking fluid.

[0084] (3) Select basic unblocking fluid based on reservoir mineral composition

[0085] Basic unblocking solution: 40 parts acid, 10 parts chelating agent, 5 parts corrosion inhibitor, 5 parts clay stabilizer, and 40 parts water.

[0086] 40 parts acid solution: 10 parts hydrochloric acid, 15 parts acetic acid, and 15 parts fluoroboric acid.

[0087] 10 parts chelating agent: 5 parts EDTA.2Na, 5 parts HEDP.

[0088] 5 parts corrosion inhibitor: imidazoline oleate.

[0089] Five parts of the clay stabilizer were: hexadecyltrimethylammonium chloride.

[0090] (4) Preparation of unblocking solution II

[0091] For medium- and low-permeability layers, first prepare all materials according to the specified ratio.

[0092] Including: water, hydrochloric acid, acetic acid, fluoroboric acid, EDTA.2Na, HEDP, oleic acid imidazoline, and hexadecyltrimethylammonium chloride.

[0093] Hydrochloric acid, acetic acid, and fluoroboric acid were added to water in sequence and stirred until homogeneous. Then, EDTA·2Na, HEDP, oleic acid imidazoline, and hexadecyltrimethylammonium chloride were added in sequence and stirred until homogeneous to obtain unblocking solution II.

[0094] (5) Using the method of injecting water back into the formation to unblock the blockage

[0095] Unblocking fluid is injected into the formation during the production process: The ratio of unblocking fluid II to reinjection water is 1:2 to 1:3 (volume ratio). A tee is installed at the wellhead to inject the unblocking fluid and reinjection water into the formation simultaneously, without interrupting production during the unblocking process. Example

[0096] The H-3 reinjection well was used as the subject of the study. Completed in 2019, the reinjection section is a sandstone reservoir, ranging from 1465 to 2163 meters. The porosity ranges from 15.65% to 35.26%, with an average of 25.3%; the permeability ranges from 89.6% to 1565.2 mD, with an average of 913 mD. The geothermal chemistry is sodium sulfate-bicarbonate type. The salinity is 2956 mg / L, dissolved solids are 2300 mg / L, total hardness (calculated as calcium carbonate) is 59.5 mg / L, pH is 8.53, classifying it as weakly alkaline and extremely soft water, with a total hardness of 65 mg / L. In 2022, compared to 2019, the well's reinjection capacity was reduced by approximately 65%.

[0097]

[0098] (1) Obtain reinjection reservoir data, including reservoir permeability and reservoir mineral composition.

[0099] The H-3 reinjection well has an average reservoir permeability of 913 mD, with layers greater than 300 mD classified as medium to high permeability.

[0100] To test the hydrochloric acid soluble content in reservoir minerals, 10g of rock sample was taken, 100ml of acid (12% HCl) was added, and the reaction was carried out for 4 hours. The weight loss of the rock sample was then used to calculate the hydrochloric acid soluble content. Three parallel samples were tested, and the values ​​were 7.15%, 7.25%, and 7.43%, respectively. The hydrochloric acid soluble content was less than 10%.

[0101] The reservoir rock samples were ground into 200-mesh powder and subjected to XRD analysis. Three parallel samples were tested, and the clay content in the reservoir minerals was 22.59%, 21.34%, and 22.69%, respectively. The clay mineral content was greater than 10%.

[0102] (2) Select unblocking fluid based on reservoir permeability

[0103] The H-3 reinjection well reservoir is a medium-to-high permeability layer, and the unblocking fluid consists of a basic unblocking fluid and a long-lasting stabilizing fluid.

[0104] Long-lasting stabilizing solution:

[0105] 30 parts stabilizer: 15 parts tetraethyl orthosilicate, 15 parts n-octyltriethoxysilane;

[0106] 10 parts alcohol: ethanol;

[0107] 2 parts emulsifier: 1 part fatty alcohol polyoxyethylene ether (O / W), 1 part Span 60 (W / O);

[0108] 2 parts dispersant: 1 part polyethylene glycol, 1 part sodium tripolyphosphate.

[0109] (3) Select basic unblocking fluid based on reservoir mineral composition

[0110] Basic unblocking solution: 40 parts acid, 10 parts chelating agent, 5 parts corrosion inhibitor, 5 parts clay stabilizer, and 40 parts water.

[0111] 40 parts acid solution: 5 parts hydrochloric acid, 5 parts sulfamic acid, 10 parts acetic acid, 5 parts citric acid, 6 parts fluoroboric acid, and 9 parts ammonium fluoride.

[0112] 10 parts chelating agent: 5 parts EDTA.2Na, 5 parts HPMA.

[0113] 5 parts corrosion inhibitor: 3 parts imidazoline oleate, 1 part polyethylene glycol ether, 1 part hexamethylenetetramine.

[0114] 5 parts clay stabilizer: polydimethyldiallyl ammonium chloride.

[0115] (4) Preparation of unblocking fluid III

[0116] For medium- to high-permeability layers, first prepare all materials according to the specified ratio.

[0117] Including: ethanol, water, tetraethyl orthosilicate, n-octyltriethoxysilane, fatty alcohol polyoxyethylene ether (O / W), EDTA.2Na, HPMA, hydrochloric acid, aminosulfonic acid, acetic acid, citric acid, fluoroboric acid, ammonium fluoride, oleic acid imidazoline, polyethylene glycol ether, hexamethylenetetramine, polydimethyldiallyl ammonium chloride, Span 60 (W / O), polyethylene glycol, and sodium tripolyphosphate.

[0118] Divide the ethanol into two portions of 30% and 70%. Divide the water into two portions of 30% and 70%.

[0119] Liquid A3 was prepared by mixing tetraethyl orthosilicate, n-octyltriethoxysilane, 30% alcohol, and Span 60 (W / O) until homogeneous.

[0120] Liquid B3 was prepared by mixing EDTA·2Na, HPMA, and 30% water until homogeneous.

[0121] Add liquid B3 to liquid A3 and stir until well mixed to form emulsion C3.

[0122] Hydrochloric acid, aminosulfonic acid, acetic acid, citric acid, fluoroboric acid, ammonium fluoride, 70% water, 70% alcohol, oleic acid imidazoline, polyethylene glycol ether, hexamethylenetetramine, polydimethyldiallylammonium chloride, fatty alcohol polyoxyethylene ether (O / W), polyethylene glycol, and sodium tripolyphosphate are added in sequence and stirred evenly to prepare liquid D3.

[0123] Finally, emulsion C3 was slowly added to liquid D3 and stirred at low speed until homogeneous to prepare unblocking solution III.

[0124] (5) Using the method of injecting water back into the formation to unblock the blockage

[0125] Unblocking fluid is injected into the formation during the production process: The ratio of unblocking fluid III to reinjection water is 1:2 to 1:3 (volume ratio). A tee is installed at the wellhead to inject the unblocking fluid and reinjection water into the formation simultaneously, without interrupting production during the unblocking process.

[0126] During construction, the injection rates (m) of wells H-1, H-2, and H-3 were recorded. 3 The relationship between injection pressure (MPa) and injection volume (m³ / h) was recorded after construction was completed. 3 The injection pressure (MPa) and the injection volume were measured. In the initial stage of unblocking, the improvement ratios of the three wells were 2.07, 3.96, and 3.52, respectively, and the injection levels returned to the initial production levels after unblocking, demonstrating a significant unblocking effect. One month after unblocking, the improvement ratios of the three wells were 2.05, 3.89, and 3.47, respectively. Compared to the initial stage of unblocking, the unblocking effect remained good, indicating that the unblocking method proposed in this invention has long-term stability.

Claims

1. A method for unblocking and enhancing the injection of sandstone reservoirs in geothermal wells, comprising the following steps: (1) Obtain reinjection reservoir data, including reservoir permeability and reservoir mineral composition. A reservoir with an average permeability of less than or equal to 300 mD is classified as a low to medium permeability reservoir, while a reservoir with an average permeability of greater than 300 mD is classified as a medium to high permeability reservoir. The reservoir mineral composition includes the content of hydrochloric acid solubles and clay content; (2) Select unblocking fluid based on reservoir permeability Medium to low permeability layers, unblocking fluid is the base unblocking fluid; The medium-to-high permeability layer is unblocking fluid composed of basic unblocking fluid and long-lasting stabilizing fluid. The basic unblocking solution is composed of the following components by weight: 20-70 parts acid solution, which consists of a base acid and a fluorinated acid or salt; 5-20 parts chelating agent; 1-5 parts corrosion inhibitor; 1-5 parts clay stabilizer; totaling 100 parts; the remainder is water. The long-lasting stabilizing liquid is composed of the following components in parts by weight: 5-30 parts stabilizer, 5-30 parts alcohol, 1-5 parts emulsifier, and 0.5-5 parts dispersant; (3) Select basic unblocking fluid based on reservoir mineral composition The amount of acid solution used is determined based on the content of hydrochloric acid soluble matter in the reservoir minerals: for hydrochloric acid soluble matter content less than or equal to 10%, the amount of acid solution used is 20-40 parts; for hydrochloric acid soluble matter content greater than 10% and less than or equal to 15%, the amount of acid solution used is 40-50 parts; for hydrochloric acid soluble matter content greater than 15%, the amount of acid solution used is 50-70 parts. The acid composition is determined based on the clay content in the reservoir minerals, specifically the ratio of basic acid to fluoride or salt: For clay content less than or equal to 5%, fluoride or salt constitutes 0-15% of the total acid content; for clay content greater than 5% but less than or equal to 10%, fluoride or salt constitutes 15-30% of the total acid content; and for clay content greater than 10%, fluoride or salt constitutes 30-45% of the total acid content. (4) Based on the results of steps (2) and (3), prepare the unblocking solution as follows: For medium to low permeability layers: add acid to the water and stir until homogeneous, then add chelating agent, corrosion inhibitor, and clay stabilizer and stir until homogeneous; For medium-to-high permeability layers: Divide the alcohol into two portions of 30% and 70%, and the water into two portions of 30% and 70%; mix the stabilizer, 30% alcohol, and W / O emulsifier evenly to prepare liquid A; mix the chelating agent and 30% water evenly to prepare liquid B; add liquid B to liquid A and stir evenly to form emulsion C; gradually add acid, 70% water, 70% alcohol, corrosion inhibitor, clay stabilizer, O / W emulsifier, and dispersant in sequence and stir evenly to prepare liquid D; finally, slowly add emulsion C to liquid D and stir at low speed until evenly mixed. (5) Inject the unblocking fluid separately or inject it into the formation along with the reinjection water during the production process.

2. The method for unblocking and increasing irrigation in sandstone reservoirs for geothermal wells as described in claim 1, characterized in that, In step (1), the hydrochloric acid soluble content in the reservoir minerals is divided into: less than or equal to 10%; greater than 10% and less than or equal to 15%; and greater than 15%. The clay content in the reservoir minerals is divided into: less than or equal to 5%; greater than 5% and less than or equal to 10%; and greater than 10%.

3. The method for unblocking and increasing irrigation in sandstone reservoirs for geothermal wells as described in claim 1, characterized in that, In step (2), the basic acid is one or more of hydrochloric acid, phosphoric acid, formic acid, acetic acid, oxalic acid, citric acid, formaldehyde, ammonium chloride, and aminosulfonic acid, and the fluorinated acid or salt is one or more of hydrofluoric acid, fluoroboric acid, and ammonium fluoride.

4. The method for unblocking and increasing irrigation in sandstone reservoirs for geothermal wells as described in claim 1, characterized in that, In step (2), the stabilizer is one or more of tetraethyl orthosilicate, trimethylethoxysilane, n-octyltriethoxysilane, cyclomethylcyclosiloxane, decamethylcyclopentasiloxane, and polytrifluoropropylmethylsiloxane; the emulsifier is a commonly used O / W emulsifier and W / O emulsifier in a 1:1 mass ratio.

5. The method for unblocking and increasing irrigation in sandstone reservoirs for geothermal wells as described in claim 1, characterized in that, In step (5), the separate injection means first diluting the unblocking fluid to 1 to 3 times with surface water, then injecting it into the formation, shutting the well in for 1 to 3 hours, and resuming normal production; the production process is injected with reinjection water, which means that the ratio of unblocking fluid to reinjection water is 1:1 to 1:5, and a T-junction is installed at the wellhead to inject the unblocking fluid and reinjection water into the formation at the same time, so that the unblocking process does not stop production.

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