深层页岩气水平井“增净压、促缝网、保充填”压裂改造模式——以四川盆地东南部丁山地区为例

由于埋藏深、地质特征复杂,致使针对中浅层页岩气藏的压裂工艺不能完全满足四川盆地东南部丁山地区上奥陶统五峰组—下志留统龙马溪组深层页岩气储层改造的需要。为此,将地质与工程研究紧密结合,优选页岩气"地质与工程双甜点"区,开展深层页岩气水平井压裂技术攻关研究,对以往仅适用于中浅层页岩气储层的压裂模式进行改进,并将改进后的压裂模式与工艺应用于丁山地区3口深层页岩气井。研究结果表明:①该区西北部深层页岩气储层具备地质、工程"双甜点"特性,天然裂缝、层理缝发育为压裂后复杂缝网的形成创造了有利条件;②基于"双甜点"区域,研究形成了"前置酸+胶液+滑溜水+胶液"混合压裂模式,采用高黏滑溜水以提高液体携砂能力及造缝效果、"控近扩远"压裂工艺以提高远井地带有效改造体积、超高压装置以提高施工排量和缝内净压力;③3口深层页岩气井经过储层改造后,增产效果显著,测试页岩气产量介于10.50×10~4～20.56×10~4 m~3/d。结论认为,改进后的压裂模式与工艺可以为该区深层页岩气储层改造提供技术途径,为深层页岩气勘探开发取得突破提供支持。

Horizontal well fracturing mode of "increasing net pressure,promoting network fracture and keeping conductivity" for the stimulation of deep shale gas reservoirs: A case study of the Dingshan area in SE Sichuan Basin

The deep shale gas reservoirs of Upper Ordovician Wufeng–Lower Silurian Longmaxi Formation in the Dingshan area of the southeastern Sichuan Basin have a great burial depth and complicated geologic features, so the fracturing technologies that are used for medium–shallow shale gas reservoirs are not suitable for their stimulation. In this paper, "double sweet spot" zones of shale gas were selected by combining engineering and geological research. The horizontal well fracturing technology suitable for deep shale gas reservoir was developed. And the fracturing mode suitable for medium–shallow shale gas reservoirs was improved. In addition, the improved fracturing mode and technology were applied in 3 deep shale gas wells in the Dingshan area. And the following research results were obtained. First, the deep shale gas reservoirs in the northwest of the Dingshan area have the characteristics of "double sweet spot" of geology and fracturing, and the development of natural fractures and bedding fractures provides a favorable condition for the formation of complex fracture networks after fracturing. Second, a combined fracturing mode of "pre acid + gel + slickwater + gel" was developed for the "double sweet spot" zones. In this mode, high-viscosity slickwater is adopted to increase the sand-carrying capacity of liquid and enhance the fracture-creating effect, the fracturing technology of "controlling the near and extending the far" can increase the effective stimulated reservoir volume far from the well, and the ultra-high pressure facility can increase the fracturing displacement and the net pressure in fractures. Third, after reservoir stimulation, 3 deep shale gas wells present remarkable stimulation results, and their shale gas production rate during the testing is in the range of 10.50×104–20.56×104 m3/d. In conclusion, the improved fracturing mode and technology can provide a technical method for the stimulation of deep shale gas reservoirs in the Dingshan area, as well as a support for the breakthrough of exploration and development of deep shale gas reservoirs.