Case Study: Dual Temporary Plugging & High Proppant Intensity Fracturing Stimulation Technique in Deep Shale Gas Play in Sichuan Basin, China

Abstract

Abstract In 2020, the total shale gas production in China has exceeded 2×1010m3, keeping China the third largest shale gas producer in the world. However, most of these yields extract from middle-deep shale gas play (TVD<3500m). Present yield cannot meet the fast-growing demand for China economic. An even larger resource of deep shale gas (TVD from 3500m to 4500m) has attracted much attention recent years. Compared with the middle-deep shale gas, there are several challenges encountered in deep shale gas development in China, such as higher formation heterogeneity, larger horizontal stress difference between maximal and minimal, stronger plastic effect and et al. These challenges may seriously affected the fracture propagation, causing a small stimulated reservoir volume (SRV) after fracturing. In order to commercially develop the deep shale gas, some comprehensive strategies should be applied to improve fracturing efficiency, such as adopting the densely distributed clusters, the high viscosity gel as pre-pad fluid, a short proppant slugging with small sand ratio, small proppant size and high strength ceramic proppant. In the meantime, the usage of temporary plugging balls and granular temporary plugging agent in one or two times increases the number of newly initiated fractures, which also is considered favorable to enlarge SRV of deep shale reservoir. One pilot shale-gas well of DYS-1 with TVD deeper than 4300m in Sichuan Basin, China was selected to conduct 30 stages fracturing stimulation test. The post-fracturing daily production reaches 412,000 m3, verifying the adaptability of above-mentioned strategies. The successful test of DYS-1 has a great significance for developing deep shale gas play in China as well as all over the world in the near future. Introduction The hydraulic fracturing technique have been widely used in unconventional oil & gas play to maximize the stimulated reservoir/rock volume (SRV)(Alexander et al., 2011). The prevailing stimulation highlights are mainly focused on densely perforation clusters (averaged distance between adjacent clusters being about 5-10m), higher proppant intensity (averaged 3-5 t/m in horizontal wellbore) and temporary plugging technique (either temporary plugging ball in horizontal wellbore or temporary plugging agent within fractures)(Cao et al., 2020; Guo et al., 2016). However, each of above-mentioned strategies may bring about ever-lasting rising of well-head treatment pressure, especially in deep shale gas play with the true vertical depth (TVD) from 3500m to 4500m. The raising of treatment may cause the treatment stopping ahead of schedule(Jinxing et al., 2018).