Investigation and Application of High-Efficiency Network Fracturing Technology for Deep Shale Gas in the Southern Sichuan Basin

Abstract

The Longmaxi Formations in the Luzhou block located in the Southern Sichuan Basin exhibit thick shale formations and huge shale gas resources and have become one of the significant blocks for large-scale production of shale gas. However, due to the natural fractures and high in situ stress and horizontal stress differences, proppants are broken and embedded severely, and complex network fractures are difficult to form, so traditional hydraulic fracturing technology cannot meet the need for profitable development of deep shale gas. In order to increase the stimulated reservoir volume and improve fracture complexity, large-scale hydraulic fracturing experiments and fracture propagation numerical simulations have been conducted based on the geology and engineering treatment difficulty of the Luzhou block to discuss the main factors influencing fracturing effectiveness. Meanwhile, two round field tests were conducted to evaluate the fracturing effectiveness, and the following study results were obtained. First, in situ stress and horizontal stress differences are the main mechanical factors, while cluster spacing and proppant injection intensity are the main fracturing parameters. Therefore, multi-cluster perforation, high-intensity proppant injection, and diversion are employed to improve fracture complexity and conductivity, thus increasing effective fracture volume. Furthermore, the second round of field tests gained remarkable results. The “short-cluster spacing + high proppant amount + variable viscosity slick water + diversion” high-efficiency fracturing technology was formed, and the average test production got to 28.6 × 10 4 m 3 /d, which represented a 64% increase over the first round. It concludes that the high-efficiency hydraulic fracturing technology contributes to increasing shale gas production, notably in the Luzhou block for deep shale gas, and provides reliable technology support and study direction for further technical optimization in this block.

Intensive geological alteration and gas accumulation in Longmaxi Formation shales at moderate and great depths: A case study of the Luzhou area in the southern Sichuan fold zone, China

“…Reformability is a key metric for determining whether shales can be effectively hydraulically fractured (Ketter et al, 2008), and it depends primarily on factors such as the brittleness and rock mechanics properties of shales in addition to the in situ stress (Zhao et al, 2022). A high brittle mineral content can facilitate the formation of fractures under external forces and is, therefore, conducive to hydraulic stimulation (Li, Li, Xu, et al, 2022).…”

“…Reformability is a key metric for determining whether shales can be effectively hydraulically fractured (Ketter et al, 2008), and it depends primarily on factors such as the brittleness and rock mechanics properties of shales in addition to the in situ stress (Zhao et al, 2022).…”

Differential Analysis of Various Moisture Phases on N2 Displacement of CH4 in Coal

“…Coal seams in China exhibit a complex structure, most of which is soft and has low permeability. To enhance the gas extraction rate from low-permeability coal seams, various methods have been employed to improve permeability, such as hydraulic permeability improvement measures, , blasting technology , , and gas fracturing technology . However, there are still some safety concerns and engineering geology limitations.…”

Mechanism and Practice of Multifracturing Using Dynamic Loads in a Low-Permeability Coal Reservoir

“…For low-permeability reservoirs, increasing the permeability is the key to improving coalbed methane (CBM) production. − Network fracturing has achieved great success in the development of shale gas in extremely low permeability reservoirs, , which has important reference significance for the development of CBM. The core of network fracturing technology is a horizontal well and multistage fracturing. − The basic theory is to use multistage fracturing to form stress interference in the reservoir. − Through bending and expansion of the fractures formed via fracturing, the primary fractures in the reservoir are connected to the maximum extent possible, thus increasing the permeability and conductivity of the reservoir. The purpose of multifracturing is to form multiple main radial fractures around the wellbore and then to extend microfractures from the multiple main fractures. , …”