Natural Gas Industry B (Jan 2016)
Breakthrough in staged fracturing technology for deep shale gas reservoirs in SE Sichuan Basin and its implications
Abstract
In the Southeastern Sichuan Basin, the deep shale reservoirs (with vertical depth over 2800 m) are complicated and diverse in reservoir mineral compositions and pore structural characteristics, with the obvious rock plasticity and nonlinear fracturing features and the high absolute difference between maximum and minimum principal stresses, due to the effect of geological setting and diagenesis. Consequently, staged fracturing operations often suffer from high fracturing pressure and propagating pressure, small fracture width, low sand–fluid ratio and fracture conductivity and difficult formation of volume fractures, which seriously influence the post-fracturing shale gas productivity. In this paper, a new combined fracturing mode (pretreatment acid + gelled fluid + slickwater + gelled fluid) and its supporting technologies were developed after a series of analysis and studies on deep rocks in terms of mechanical property, earth stress characteristics, fracturing characteristics and fracture morphology characteristics. Field application shows that geologic breakthrough was realized in Longmaxi Fm of Lower Silurian in Well Dingye 2HF, with absolute open flow (AOF) of 10.5 × 104 m3/d after fracturing. And it was expected to reach commercial breakthrough in Qiongzhusi Fm of Lower Cambrian in Well Jinye 1HF, with AOF of 10.5 × 104 m3/d after fracturing. Finally, the following conclusions are reached. First, it is hard to form complex fractures in deep shale and the fracturing technologies applicable for it should be different from those used in mid–deep zones. Second, the established fracturing pressure model can provide an effective way for deep-zone fracturing pressure prediction. Third, reducing operation pressure is one of the key measures to ensure successful deep-zone fracturing. Fourth, besides good material basis, it is crucial to increase the complexity of induced fractures and generate high-conductivity fractures in order to guarantee successful fracturing in deep shale.
Keywords
