Technology and Application of Segmented Temporary Plugging Acid Fracturing in Highly Deviated Wells in Ultradeep Carbonate Reservoirs in Southwest China

[Image: see text] The Shuangyu gas reservoirs in China has a reservoir depth of more than 7000 m and a reservoir temperature of 160 °C. It is a fractured porous carbonate gas reservoir, and the gas wells mainly establish production by acid fracturing. In the early stage, the Shuangyu gas reservoirs was mainly developed with vertical wells. After acid fracturing, the natural gas production was low and declined rapidly. To obtain higher natural gas production, a large number of highly deviated wells have been deployed in the Shuangyu gas reservoirs. Because the diameter of a highly deviated well in the Shuangyu gas reservoirs is small, a subsection tool cannot be operated inside it, so it can only adopt temporary plugging acid fracturing. In this paper, a resistance-reducing acid with low friction resistance is optimized and a set of temporary plugging agents with low dissolution rate in the acid solution are selected through laboratory tests. A dynamic temporary plugging instrument is used to evaluate the plugging ability of a temporary plugging agent with different concentrations and combinations for fractures with widths of 2 and 4 mm, developing a temporary plugging agent formulation suitable for temporary plugging segmented acid fracturing of the Shuangyu gas reservoirs. In the YY666 well, the application of the research results of this paper has successfully achieved a three-stage temporary plugging acid fracturing, and the natural gas production after fracturing has been increased by 3–4 times compared with those of surrounding wells.