Centrealoil--Crosslinked acid fracture

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The development of acid fluid system of Lower Paleozoic carbonate reservoir acid fracturing are all for the purpose of reduce acid filtration and change uneven acid distribution of the same layer or interlayer in reservoir. Because of reservoir heterogeneity and the interlayer difference , in the acid fracturing process, common acid including thickening acid is always preferred to corrosion for high permeability zone. Once formed the main acid soluble channel, the subsequent main acid will be along the main acid soluble channel to promote the acid soluble and continue the reaction, which leads to low permeability zone see too little or no acid, seriously affect the effect of reservoir reconstruction. In order to reduce acid filtration, the oilfield has used preflush acidification, the multi-stage injection acidification and other technology. However, because guar gum gelling as preflush or block injection liquid will be gel breaking immediately when exposed to acid, which still couldn't prevent a large number of acid filtration, especially for ultra-low permeability Lower Paleozoic carbonate reservoir can not achieve the purpose of making a long slit, affect the acidification effect. At the same time, the implementation of the above process requires a lot of guar gum gelling as prepad fluid or spacer fluid, so the cost of construction will be multiplied. Moreover, thickening acid will not degrade when flowback, and it has high viscosity, in addition to causing the difficulty of flowback, it will produce the damage of polymer retention to the reservoir.

In order to achieve the purpose of full development of low permeability gas field Lower Paleozoic carbonate reservoir, our company has developed a polymer thickener and matching crosslinking agent. Thickener is introduced a number of acid resistance groups and carboxyl in the process of polymerization, carboxyl is fully stretched under the strong acid condition and crosslinked with crosslinking agent. The system by a linear structure into a network structure, so as to achieve the purpose of reducing acid filtration. Moreover, owing to changing into a network structure of crosslinked acid gel system and hanging, its initial viscosity is greater than 800mPa.s, so it can meet the construction requirements of building long slit. Because the initial viscosity of acid gel is very high, the gel and carbonate is almost no reaction in the initial stage of contact, filtration is very small, after it is broken, a large number of H ⁺ is released, which can make hydrochloric acid reacted sufficiently with different permeability reservoir, so as to achieve the purpose of uniform acid distribution in reservoir. The technology has been applied more than 50 wells in Xinjiang oilfield, and has obvious yield-increasing effect.

Characteristics:

①The dosage range of HCl is from 7% to 20%, and it is beneficial for reservoir to adjust different ratio of acid.

②The system has good temperature tolerance and shear tolerance properties, its viscosity is greater than                 100mPa.s at 90℃, 170s^-1 continuous shear for an hour.

③Thickener has no solid phase, gel breaking liquid has no residue, and less damage to the reservoirs.

④It can greatly reduce the acid fluid filtration in reservoir, and is beneficial for reservoir to build long slit.

⑤It is suitable for the reservoir temperature (80~120℃) carbonate reservoir reconstruction.

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