Abstract
Hydraulic fracture initiation and propagation are extremely important on deciding the production capacity and are crucial for oil and gas exploration and development. Based on a self-designed system, multi-perforation cluster-staged fracturing in thick tight sandstone reservoir was simulated in the laboratory. Moreover, the technology of staged fracturing during casing completion was achieved by using a preformed perforated wellbore. Three hydraulic fracturing methods, including single-perforation cluster fracturing, multi-perforation cluster conventional fracturing and multi-perforation cluster staged fracturing, were applied and studied, respectively. The results clearly indicate that the hydraulic fractures resulting from single-perforation cluster fracturing are relatively simple, which is difficult to form fracture network. In contrast, multi-perforation cluster-staged fracturing has more probability to produce complex fractures including major fracture and its branched fractures, especially in heterogeneous samples. Furthermore, the propagation direction of hydraulic fractures tends to change in heterogeneous samples, which is more likely to form a multi-directional hydraulic fracture network. The fracture area is greatly increased when the perforation cluster density increases in multi-perforation cluster conventional fracturing and multi-perforation cluster-staged fracturing. Moreover, higher perforation cluster densities and larger stage numbers are beneficial to hydraulic fracture initiation. The breakdown pressure in homogeneous samples is much higher than that in heterogeneous samples during hydraulic fracturing. In addition, the time of first fracture initiation has the trend that the shorter the initiation time is, the higher the breakdown pressure is. The results of this study provide meaningful suggestions for enhancing the production mechanism of multi-perforation cluster staged fracturing.
Highlights
Tight sandstone is a reservoir with a low to ultra-low porosity and permeability (Becker et al, 2017; Lu et al, 2015; Zhou et al, 2018)
A series of hydraulic fracturing experiments in thick tight sandstone reservoirs have been conducted in this paper
multi-perforation cluster staged fracturing (MPCSF) can lead to a complex fracture system, especially in heterogeneous samples
Summary
Tight sandstone is a reservoir with a low to ultra-low porosity and permeability (Becker et al, 2017; Lu et al, 2015; Zhou et al, 2018). Hydraulic fracturing is one of the most effective ways for enhancing oil and gas recovery and has been applied in tight sandstone oil and gas exploitation for years. As an important part of hydraulic fracturing, research on hydraulic fracture initiation and propagation has always been a topic of increased interest (Bohloli and Pater, 2006; Brudy and Zoback, 1999; Gale et al, 2007; Huang et al, 2017; Lee, 2015; Li et al, 2014; Liu et al, 2018). Hydraulic fracturing experiments on coalbed methane reservoirs were performed by Liu et al (2018), and it was found that new hydraulic fractures prefer to propagate along the preexisting fracture direction at a small approaching angle
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