A thickener for hot dry rock fracturing and its preparation method

Abstract

This invention provides a thickener for hot dry rock fracturing and its preparation method. The thickener comprises a compound with the following molecular formula: where n is any one or more integers from 4000 to 5000. The preparation method of the thickener comprises the following steps: S1: Stir the components in the following weight ratios to prepare an aqueous phase: 15-20 parts acrylamide, 8-12 parts N-isopropylacrylamide, 5-10 parts 4-acrylamidohexadecyloxybenzene, 4-8 parts dimethylhexadecylallylammonium chloride, and 100 parts water; S2: Stir the components in the following weight ratios to prepare an oil phase: 4-6 parts emulsifier and 30-50 parts white oil; S3: Mix the aqueous phase and the oil phase, stir, heat to 40-60°C, add an initiator dropwise, continue the reaction for 3-5 hours, cool to room temperature, and obtain the thickener. The fracturing fluid prepared by mixing the thickener of this invention with water has good temperature resistance, drag reduction performance, and viscosity-changing properties, which can meet the needs of hot dry rock fracturing operations.

Description

Technical Field

[0001] This invention relates to the field of hot dry rock development technology, and more specifically to a thickener for hot dry rock fracturing and its preparation method. Background Technology

[0002] Hot dry rock (HDR) refers to high-temperature rock masses containing little or no internal fluid, typically buried at depths exceeding 3 km, with underground temperatures exceeding 150°C. As a vast and renewable clean energy source, the exploitation of HDR has become an important direction for new energy development research worldwide. my country possesses abundant HDR geothermal resources, with current proven reserves equivalent to 5 trillion tons of liquefied petroleum gas. Enhanced geothermal systems (EGS) utilize hydraulic fracturing to create artificial geothermal reservoirs within HDR masses, representing an effective method for developing HDR resources. By creating complex fracture systems through hydraulic fracturing that connect injection and production wells, the necessary flow channels are provided for the geothermal circulation system, increasing the heat exchange area. The stored thermal energy in the HDR is extracted through the circulation of heat-carrying fluids, achieving efficient development of HDR thermal energy.

[0003] However, hot dry rocks are complex in lithology, possessing high mechanical strength and heterogeneity. Fracturing hot dry rocks presents challenges such as high operating pressure, severe leakage, limited fracture propagation, and high reservoir temperature. Conventional fracturing fluids are often insufficient to meet the operational requirements, frequently resulting in severe leakage, difficulty in fracture propagation, and excessively high operating pressure. Currently, the most common solution is to control the fracturing fluid injection method, such as injecting pre-fracturing fluid before conventional fracturing fluid injection, and / or injecting fracturing fluid in batches at different flow rates. However, these methods cannot fundamentally solve the aforementioned problems.

[0004] Therefore, it is essential to develop a liquid system for hot dry rock fracturing to meet the needs of hot dry rock fracturing operations and realize the efficient development of hot dry rock thermal energy. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, the present invention aims to provide a thickener for hot dry rock fracturing. This thickener, when mixed with water, produces a fracturing fluid with excellent temperature resistance, drag reduction, and viscosity-enhancing properties, thus meeting the requirements of hot dry rock fracturing operations. The present invention also provides a method for preparing this thickener.

[0006] According to the present invention, a thickener for hot dry rock fracturing is provided, comprising compounds with the following molecular formula:

[0007]

[0008] Where n is any one or more integers between 4000 and 5000.

[0009] According to the present invention, a method for preparing a thickener for hot dry rock fracturing is provided, comprising the following steps:

[0010] S1: Mix the following components in the indicated weight ratios to prepare an aqueous phase: 15-20 parts acrylamide, 8-12 parts N-isopropylacrylamide, 5-10 parts 4-acrylamidohexadecyloxybenzene, 4-8 parts dimethylhexadecylallylammonium chloride, and 100 parts water.

[0011] S2: Mix the following components in the indicated weight ratios to prepare the oil phase: 4-6 parts emulsifier, 30-50 parts white oil;

[0012] S3: Mix the aqueous phase and oil phase, stir, heat to 40-60℃, add initiator dropwise, continue the reaction for 3-5 hours, cool to room temperature, and obtain thickener.

[0013] According to one embodiment of the present invention, the emulsifier is a mixture of SDS and TX-4.

[0014] According to one embodiment of the present invention, the weight ratio of SDS to TX-4 is 1:(0.9-1.1).

[0015] According to one embodiment of the present invention, the initiator is V50.

[0016] According to one embodiment of the present invention, the weight of V50 added is 0.008%-0.012% of the weight of the solute in the aqueous phase.

[0017] According to one embodiment of the present invention, in step S3, nitrogen gas is introduced into the mixture to remove oxygen while stirring.

[0018] By adopting the above technical solution, the present invention has at least the following beneficial effects:

[0019] 1. The preparation method of the thickener for hot dry rock fracturing according to the present invention has simple steps and is convenient for field use;

[0020] 2. The thickener for fracturing hot dry rock according to the present invention has strong temperature resistance and can be used normally in specific working environments with high temperatures in hot dry rock reservoirs without failing due to excessive temperature.

[0021] 3. The thickener for hot dry rock fracturing according to the present invention has good drag reduction and viscosity-enhancing properties, which can reduce formation leakage and effectively solve the problems of high pressure, severe leakage and limited fracture extension in hot dry rock fracturing. Detailed Implementation

[0022] The technical solution of the present invention will be described in detail below through embodiments. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present disclosure.

[0023] The thickener for hot dry rock fracturing according to the present invention comprises compounds with the following molecular formula:

[0024]

[0025] Where n is any one or more integers between 4000 and 5000. Therefore, a thickener may contain one compound with the same n value, or it may contain multiple compounds with different n values.

[0026] The aforementioned thickener for hot dry rock fracturing can be prepared according to the preparation method of the present invention, which generally includes the following steps:

[0027] S1: Mix the following components in the indicated weight ratios to prepare the aqueous phase: 15-20 parts acrylamide, 8-12 parts N-isopropylacrylamide, 5-10 parts 4-acrylamidohexadecyloxybenzene, 4-8 parts dimethylhexadecylallylammonium chloride, and 100 parts water.

[0028] S2: Mix the following components in the indicated weight ratios to prepare the oil phase: 4-6 parts emulsifier and 30-50 parts white oil.

[0029] In embodiments of the present invention, the emulsifier may be a mixture of SDS (sodium dodecyl sulfate) and TX-4 (nonylphenol polyoxyethylene (4) ether). The preferred weight ratio of SDS to TX-4 is 1:(0.9-1.1).

[0030] S3: Mix the aqueous phase and oil phase, stir, heat to 40-60℃, add initiator dropwise, continue the reaction for 3-5 hours, cool to room temperature, and obtain thickener.

[0031] In embodiments of the present invention, the initiator may be V50 (azobisisobutyramidine hydrochloride). Preferably, the weight of V50 added is 0.008%-0.012% of the weight of the solutes (acrylamide, N-isopropylacrylamide, 4-acrylamidohexadecyloxybenzene, and dimethylhexadecylallylammonium chloride) in the aqueous phase. Further, nitrogen gas may be introduced into the mixture during stirring in this step to remove the oxygen generated in the reaction. Those skilled in the art can set a reasonable nitrogen gas introduction rate and amount according to actual operating conditions.

[0032] The above method will be further explained below with reference to specific parameters.

[0033] Example 1

[0034] The thickener of Example 1 of this invention is composed of the following components by weight:

[0035]

[0036] The emulsifier contains SDS and TX in a weight ratio of 1:0.9.

[0037] The specific preparation method includes the following steps:

[0038] S1: Mix acrylamide, N-isopropylacrylamide, 4-acrylamidohexadecyloxybenzene, dimethylhexadecylallylammonium chloride and water in the above weight ratio to prepare an aqueous phase.

[0039] S2: Mix the emulsifier and white oil in the above weight ratio evenly to prepare the oil phase;

[0040] S3: Mix the aqueous phase obtained in S1 and the oil phase obtained in S2, stir and introduce nitrogen gas, heat to 40°C, add initiator V50 at 0.008% of the solute weight in the aqueous phase, continue the reaction for 3 hours, cool to room temperature, and obtain the thickener.

[0041] Example 2

[0042] The thickener of Example 2 of this invention is composed of the following components by weight:

[0043]

[0044] The emulsifier contains SDS and TX in a weight ratio of 1:1.0.

[0045] The specific preparation method includes the following steps:

[0046] S1: Mix acrylamide, N-isopropylacrylamide, 4-acrylamidohexadecyloxybenzene, dimethylhexadecylallylammonium chloride and water in the above weight ratio to prepare an aqueous phase.

[0047] S2: Mix the emulsifier and white oil in the above weight ratio evenly to prepare the oil phase;

[0048] S3: Mix the aqueous phase obtained in S1 and the oil phase obtained in S2, stir and introduce nitrogen gas, heat to 55°C, add initiator V50 at 0.01% of the solute weight in the aqueous phase, continue the reaction for 4 hours, cool to room temperature, and obtain the thickener.

[0049] Example 3

[0050] The thickener of Example 3 of this invention is composed of the following components by weight:

[0051]

[0052] The emulsifier contains SDS and TX in a weight ratio of 1:1.1.

[0053] The specific preparation method includes the following steps:

[0054] S1: Mix acrylamide, N-isopropylacrylamide, 4-acrylamidohexadecyloxybenzene, dimethylhexadecylallylammonium chloride and water in the above weight ratio to prepare an aqueous phase.

[0055] S2: Mix the emulsifier and white oil in the above weight ratio evenly to prepare the oil phase;

[0056] S3: Mix the aqueous phase obtained in S1 and the oil phase obtained in S2, stir and introduce nitrogen gas, heat to 45°C, add initiator V50 at 0.012% of the solute weight in the aqueous phase, continue the reaction for 3 hours, cool to room temperature, and obtain the thickener.

[0057] Example 4

[0058] The thickener of Example 4 of this invention is composed of the following components by weight:

[0059]

[0060]

[0061] The emulsifier contains SDS and TX in a weight ratio of 1:1.1.

[0062] The specific preparation method includes the following steps:

[0063] S1: Mix acrylamide, N-isopropylacrylamide, 4-acrylamidohexadecyloxybenzene, dimethylhexadecylallylammonium chloride and water in the above weight ratio to prepare an aqueous phase.

[0064] S2: Mix the emulsifier and white oil in the above weight ratio evenly to prepare the oil phase;

[0065] S3: Mix the aqueous phase obtained in S1 and the oil phase obtained in S2, stir and introduce nitrogen gas, heat to 60°C, add initiator V50 at 0.009% of the solute weight in the aqueous phase, continue the reaction for 3 hours, cool to room temperature, and obtain the thickener.

[0066] Example 5

[0067] The thickener of Example 5 of this invention is composed of the following components by weight:

[0068]

[0069] The emulsifier contains SDS and TX in a weight ratio of 1:1.1.

[0070] The specific preparation method includes the following steps:

[0071] S1: Mix acrylamide, N-isopropylacrylamide, 4-acrylamidohexadecyloxybenzene, dimethylhexadecylallylammonium chloride and water in the above weight ratio to prepare an aqueous phase.

[0072] S2: Mix the emulsifier and white oil in the above weight ratio evenly to prepare the oil phase;

[0073] S3: Mix the aqueous phase obtained in S1 and the oil phase obtained in S2, stir and introduce nitrogen gas, heat to 50°C, add initiator V50 at 0.011% of the solute weight in the aqueous phase, continue the reaction for 4 hours, cool to room temperature, and obtain the thickener.

[0074] The thickeners obtained in Examples 1-5 were tested for various properties, and the following test results were obtained.

[0075] 1. Drag reduction rate

[0076] The thickeners prepared in Examples 1-5 were used to prepare fracturing fluids in the form of 0.1% aqueous solutions. The drag reduction performance was evaluated according to the standard "NB / T14003.1-2005 Shale Gas Thickeners Part 1: Slickwater Performance Indicators and Evaluation Methods". The results are shown in Table 1.

[0077] Table 1 Resistance Reduction Ratio

[0078] Example 1 Example 2 Example 3 Example 4 Example 5 Drag reduction rate % 72.1 76.2 75.5 73.6 74.8

[0079] As shown in Table 1, the drag reduction rates of Examples 1-5 are all greater than 70%, indicating that the target material of the present invention has good drag reduction performance and can effectively reduce the pressure of on-site construction.

[0080] 2. Viscosity variation properties

[0081] The thickeners prepared in Examples 1-5 were formulated into fracturing fluids in proportion to form aqueous solutions. The viscosity at different concentrations was tested, and the results are shown in Table 2.

[0082] Table 2 Viscosity properties

[0083]

[0084]

[0085] As shown in Table 2, the viscosity of Examples 1-5 varies at different concentrations, indicating that the target material of the present invention has good viscosity-changing properties.

[0086] 3. Temperature resistance

[0087] The thickeners prepared in Examples 1-5 were mixed at a ratio of 0.7% to form an aqueous fracturing fluid, which was then subjected to standard treatment at 200°C for 170 seconds. -1Under the given conditions, the material was sheared for 120 minutes, and the results are shown in Table 3.

[0088] Table 3 Temperature Resistance

[0089]

[0090] As shown in Table 3, the viscosity after shearing in Examples 1-5 is above 30 mPa·s, which meets the standard requirements, indicating that the target material of the present invention has good temperature resistance.

[0091] In summary, the thickener prepared according to the method of the present invention has strong temperature resistance and can be used normally in specific working environments with high temperatures in hot dry rock reservoirs without failing due to excessive temperature. Its good drag reduction and viscosity-enhancing properties can reduce formation leakage and effectively solve the problems of high pressure, severe leakage, and limited fracture extension in hot dry rock fracturing construction, thus meeting the needs of hot dry rock fracturing construction.

[0092] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately. Furthermore, various different embodiments of this disclosure can also be combined arbitrarily, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for preparing a thickening agent for hot dry rock fracturing, characterized by, Comprising the following steps: S1: uniformly stirring the following components in weight ratio to prepare the water phase: acrylamide 15-20 parts, N-isopropyl acrylamide 8-12 parts, 4-acrylamidohexadecyloxybenzene 5-10 parts, dimethylhexadecyl allyl ammonium chloride 4-8 parts, water 100 parts; S2: uniformly stirring the following components in weight ratio to prepare the oil phase: emulsifier 4-6 parts, white oil 30-50 parts; S3: mixing the water phase and the oil phase, stirring, heating to 40-60℃, adding initiator dropwise, continuing to react for 3-5 hours, cooling to room temperature to obtain the thickening agent, the thickening agent comprising a compound with the following molecular formula: ， Wherein, n is any one or more of 4000-5000 integers.

2. The production method according to claim 1, characterized by, The emulsifier is a mixture of SDS and TX-4.

3. The preparation method according to claim 2, characterized in that, The weight ratio of SDS and TX-4 is 1: (0.9-1.1).

4. The method of claim 1, wherein, The initiator is V50.

5. The production method according to claim 4, characterized by, The weight of V50 dropwise accounts for 0.008%-0.012% of the weight of solutes in the water phase.

6. The method of claim 1, wherein, In step S3, nitrogen is introduced into the mixed solution to remove oxygen while stirring.

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