Variant-hydrochloric-acid-concentration acid fracturing method for carbonate reservoir

Abstract

The invention relates to variant-hydrochloric-acid-concentration acid fracturing method for a carbonate reservoir. The variant-hydrochloric-acid-concentration acid fracturing method is characterized by sequentially injecting high-concentration hydrochloric acid and low-concentration hydrochloric acid into the stratum and particularly comprises the following procedures: (1) injecting slick water into the stratum; (2) injecting a fracturing fluid into the stratum, wherein the viscosity of the fracturing fluid is 100-400 mPa.s; (3) injecting a gelled acid system in which the mass percent of HCL is 20 percent into the stratum; (4) injecting a gelled acid system in which the mass percent of HCL is 15 percent into the stratum; and (5) injecting slick water into the stratum. The volume ratios of liquid injected in the procedures (1), (2), (3), (4) and (5) in the total amount of liquid in the stratum are respectively 3-10 percent, 40-60 percent, 20-30 percent, 10-20 percent and 5-15 percent in sequence, and the volume unit is m<3>.

Description

technical field [0001] The invention relates to the technical field of oil and gas field development, in particular to an acid fracturing method for variable hydrochloric acid concentration in carbonate rock reservoirs. Background technique [0002] The main components of carbonate reservoirs are calcium carbonate and magnesium carbonate, and their mass percentages are above 95%. For such reservoirs, acid fracturing is usually used to achieve the purpose of stimulation. The acid fracturing process is also called the acid fracturing process. Its principle is that after the fracturing is hydraulically opened, the acid system with hydrochloric acid as the main component is injected, and the surface of the fracturing fracture is etched by the reaction of hydrochloric acid and carbonate rock. , so that the surface of the fracture becomes uneven, so that after the fracture is closed, a certain oil flow channel will be formed between the fracture walls, so that the formation fluid...

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Problems solved by technology

However, after the acid fracturing construction, the residual acid after the reaction between the acid liquid system and the carbonate rock reduces the cloud point of the demulsifier, enhances the lipophilicity of the demulsifier, and the demulsifier adsorbed on the oil-water interface disperses and transfers to the oil phase, resulting in The demulsification ability of the oil is weakened (Hu Wenli, The influence of residual acid flowback fluid on the demulsification effect of crude oil emulsion, Fault Block Oil and Gas Field, 2007, 14(4): 78-79)

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