Acrylamide copolymer, preparation method and application thereof

Abstract

The present invention discloses an acrylamide copolymer, a preparation method and an application thereof. The acrylamide copolymer contains a structure unit A, a structure unit B and a structure unit C, wherein the structure unit A is the structure unit represented by a formula (1), the structure unit B is the structure unit represented by a formula (2), the structure unit C is the structure unit represented by a formula (3), the acrylamide copolymer comprises 5-95 mol% of the structure unit A, 2.5-90 mol% of the structure unit B and 0.5-90 mol% of the structure unit C by adopting the total number of the moles of the structure units in the acrylamide copolymer as the reference, and the viscosity-average molecular weight of the acrylamide copolymer is 2-15 million. The acrylamide copolymer of the present invention has characteristics of high drag reduction efficiency, high heat resistance, high salt tolerance, good high-shear resistance, good water solubility, good compatibility with the clay stabilizer (alcohol), low viscosity-average molecular weight and low damage on stratum.

Description

technical field [0001] The invention relates to an acrylamide copolymer, two preparation methods of the acrylamide copolymer and the application of the acrylamide copolymer as a drag reducer. Background technique [0002] As a typical representative of the utilization of unconventional oil and gas resources - the exploitation of shale gas (oil) resources has become a revolution in the field of unconventional oil and gas resources in the world. Key technologies. Due to the extremely tight oil and gas reservoirs such as shale gas reservoirs have the characteristics of extremely low permeability (generally less than 0.5mD), high fracturing pressure, and easy formation damage. It must be exploited by "reducing water (slick water) fracturing" technology. [0003] "Slick water (slick water) fracturing" is a type of hydraulic fracturing. Compared with the current conventional fracturing system (modified guar gum cross-linking system), drag-reducing water (slick water) fracturing...

AI Technical Summary

Problems solved by technology

[0005] At present, the use of guar gum, cellulose and their derivatives as drag reducing agents in drag reducing water fracturing has improved the pumping capacity and reduced the frictional resistance in pipelines to a certain extent (US5697444, US5271466), but still cannot meet the The requirements for drag-reducing water fracturing are mainly due to the following shortcomings of the above-mentioned biopolymers: (1) limited drag-reducing performance; (2) due to the small amount of insoluble matter in guar gum, cellulose and their derivatives, it is easy to cause damage to the formation; (3) The dissolution time is longer

[0006] In the construction of drag reducing water fracturing, acrylamide polymers (partially hydrolyzed acrylamide or anionic acrylamide copolymer) are often used as drag reducing agents in drag reducing water fracturing, which greatly improves pump injection and drainage. However, when used as a drag reducing agent for shale gas reservoir drag reducing water fracturing, there are the following important defects: (1) In order to reduce the "water-sensitive effect" in the fracturing process, suppress shale gas For the hydration expansion of clay components in rocks, small molecule cationic clay stabilizers (such as potassium chloride, tetramethylammonium chloride, etc.) must be added to the fracturing fluid

Partially hydrolyzed acrylamide or anionic acrylamide copolymers and their emulsion products have poor compatibility with the above clay stabilizers and are prone to precipitation; (2) Partially hydrolyzed acrylamide or anionic acrylamide copolymers are used as shale gas reservoirs The drag reducing agent used in drag reducing water fracturing has poor anti-filtration performance, and this kind of drag reducing water fracturing fluid is very easy to filter out into the formation; (3) The temperature resistance and salt resistance are poor, especially in high salinity Under the condition of high divalent ion content, the molecular structure is unstable, and the resistance reduction effect decreases rapidly

[0007] Patent US20090298721A1 discloses a formula of drag reducing water fracturing fluid: add 0.5 gallons of acrylamide-co-acrylic acid copolymer (FR-56 TM ) and other anionic acrylamide copolymer emulsions as drag reducing agents, and then adding 0.15wt% sodium carbonate or EDTA-2Na and other complexing agents, the drag reducing water fracturing fluid has excellent drag reducing performance, and the average indoor drag reducing rate reaches 65.0%, the salt resistance (especially the tolerance to divalent calcium ions) has been improved to a certain extent, but this kind of drag-reducing water fracturing system is used as a shale gas drag-reducing water fracturing fluid, and there are the following problems : (1) The compatibility with clay stabilizer and alcohol is poor, and precipitation is easy to occur; (2) The anti-filtration performance is poor, and this kind of drag-reducing water fracturing fluid is easy to filter into the formation; (3) In actual construction, the "water-sensitive effect" is significant; (4) "water plugging" is very easy to occur; (5) the high-speed shear resistance is poor, unstable under high-speed shear, and the resistance reduction rate drops rapidly; (6) ) The temperature and salt resistance is poor, especially under the conditions of high salinity and high divalent ion content, the molecular structure is unstable, and the drag reduction effect drops rapidly; (7) It is not easy to degrade, and it is easy to cause permanent damage to extremely dense shale formations type damage, pollute the formation, and then affect oil and gas production

However, this type of drag reducing agent has a high molecular weight, is not easy to degrade, and is likely to cause permanent damage to tight shale

[0009] But how to further improve the high-speed shear resistance of the drag reducer, improve the inhibition and fluid loss resistance of the fracturing fluid to clay, improve the stability of the drag reduction rate under high-temperature, high-salt, and high-shear conditions, and reduce the polymer Damage to formations remains an unresolved issue

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