EffectiveFracturing Technology of Normal Pressure Shale Gas Wells

Abstract

ABSTRACT There is abundant normal pressure shale gas resource in China. However, it is hard to acquire commercial breakthroughs because of the relative low initial gas production and rapid decline in normal pressure shale gas play such as Pengshui Block, etc. Normal pressure shale gas play has developed economically, but the differences in geological characteristics of normal pressure shale gas in China and US demonstrates that both "surface" and "underground" conditions of shale gas in China are worse than those in US, bringing further challenges for domestic hydraulic fracturing technology. On the basis of continuous "decreasing cost & increasing production", accordingly low cost fracturing technology for normal pressure shale gas wells was put forward, i.e., multi fractures initiating, extending and propped uniformly in one stage, with more clusters and higher sand intensity. Technological system chain, i.e., shale fracability evaluation - collaborative optimization design for multi fracturing parameter – technique of multi fractures uniformly initiating and extending, is also developed to improve fracture complexity and effective stimulation reservoir volume in normal shale gas wells, as well as decrease the hydraulic fracturing treatment cost. An application well located in SE Chongqing shows good production potential. The research could provide fracturing references for horizontal wells in similar shale gas play. INTRODUCTION Normal pressure shale gas refers to shale gas reservoirs with a formation pressure coefficient of 0.8 to 1.2. In the US, shale gas has been successfully developed commercially in the Fayetteville and Marcellus atmospheric areas, especially in the Marcellus shale field, which has been the largest shale gas field in the US since 2013, with annual production approaching 40% of total US shale gas production. Currently, overpressured shale gas, represented by the shale gas fields in Fuling and Shunan, is the first to gain commercial development in China, with production up to 102.9×108m3 (Zou et al.,2017; He et al.,2018). However, the initial post-pressure test production of atmospheric shale gas wells in Pengshui, Wulong and Dingshan is generally less than 6×104m3/d, with stable gas production being less than 3×104m3/d. Currently, the total engineering cost of a single well is typically over RMB 60 million, so only a reduction in engineering operating costs is possible to increase the economic development value of a normal pressure shale gas well (Bian et al.,2020; Hu et al.,2019). China is rich in normal-pressure shale gas reserves, with 8.2×104km2 (no more than 3500m) of shale distribution in the Sichuan Basin and the surrounding Silurian system, of which 75.6% is normal pressure shale gas, with geological resources of up to 19.8×1012m3. In this paper, a set of low-cost fracturing techniques is initially explored for the geological characteristics of normal shale gas in China by comparing the geological features and fracturing techniques of normal shale gas between China and the United States, with a view to revitalizing the huge normal shale gas resources in our country.