Acrylamide copolymer, and preparation method and application thereof

Abstract

The invention discloses an acrylamide copolymer, and a preparation method and an application thereof. The acrylamide copolymer contains a constitutional unit A, a constitutional unit B, a constitutional unit C and a constitutional unit D, wherein the constitutional unit A is a constitutional unit represented by formula (1) and / or a constitutional unit represented by formula (2), the constitutional unit B is at least one of constitutional units represented by formula (3), formula (4), formula (5) and formula (6) respectively, the constitutional unit C is a constitutional unit represented by formula (7), and the constitutional unit D is a constitutional unit represented by formula (5) and / or a constitutional unit represented by formula (9); and the viscosity average molecular weight of the acrylamide copolymer is 5,000,000-18,000,000. The acrylamide copolymer has the advantages of high drag reduction rate, high heat and salt resistance, good high-shear resistance, good water solubility, good compatibleness with clay inhibitors (alcohol), and low damages to the stratum.

Description

technical field [0001] The invention relates to an acrylamide copolymer and its preparation method and application. 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 does not rely on high-viscosity colloid to carry sand, but carries sand wit...

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Problems solved by technology

[0005] At present, the use of guar gum and its derivatives, cellulose and its derivatives as the drag reducing agent in drag reducing water fracturing has improved the pump injection displacement to a certain extent and reduced the frictional resistance in the pipeline (US 5697444, US 5271466 ), but still cannot meet the requirements of drag-reducing water fracturing, mainly due to the following disadvantages of the above-mentioned biopolymers: (1) limited drag-reducing performance; (2) due to guar gum and its derivatives, cellulose and its derivatives A small amount of insoluble matter can easily cause damage to the formation; (3) The dissolution time is long

[0006] In the drag reducing water fracturing construction, acrylamide polymers (partially hydrolyzed polyacrylamide) are mostly used as the drag reducing agent in the drag reducing water fracturing, which greatly increases the pump injection displacement and reduces the flow rate in the pipeline. However, when used as a drag reducing agent for water fracturing in shale gas reservoirs, there are the following important defects: (1) In order to reduce the "water-sensitive effect" in the fracturing process, the clay component in shale is suppressed; Hydration expansion helps the flowback of fracturing fluid to reduce "water plugging". Part of alcohol must be added to fracturing fluid, but the compatibility of partially hydrolyzed acrylamide and its emulsion products with alcohol is poor, and precipitation is easy to occur; ( 2) Partially hydrolyzed polyacrylamide used as a drag reducing agent for drag reducing water fracturing in shale gas reservoirs has poor anti-filtration performance, and this kind of drag reducing water fracturing fluid is very easy to filter out into the formation; (3) Temperature resistance Salt resistance is poor, especially under the conditions of high salinity and high divalent ion content, the molecular structure is unstable, and the drag-reducing effect drops rapidly; (4) Traditional high-molecular-weight acrylamide polymers are not easy to degrade and easy to degrade. Permanent damage to extremely dense shale formations

[0007] Patent US 20090298721A1 discloses a formula for 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 alcohol is poor, and it is easy to produce precipitation when it interacts with methanol and other alcohols; (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 the actual construction, the "water-sensitive effect" is significant; (4) "water blockage" 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-reducing effect drops rapidly; Permanent damage, contaminating the formation, and then affecting oil and gas production

The copolymer with this kind of structure has better compatibility with alcohol, and better compatibility with clay inhibitors (such as KCl), the "water-sensitive effect" is not significant, and it is not easy to "water blockage". Not easy to degrade, easy to cause permanent damage to extremely tight shale formations

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