Study on Compound Fracturing of Maokou Formation Marl in Southeast Sichuan

The Maokou formation in the southeast Sichuan is shallow buried. It is rich in sensitive minerals and has low porosity and low permeability. In reservoir stimulation operations, multi-cluster limited entry perforation, friction-reduced water with sand and fracturing with compound clear acids techniques were used to increase the volume of reservoir formations to be stimulated and to improve the conductivity of formation fractures. Based on the rock mechanics parameters, the artificial fracture density was increased using intensive cut perforation technique, the spacing between two fractures was optimized to 10 – 15 m by increasing the inducing force. When the fluid volume in a single section was 1,600 – 1,800 m³, and the ratio of friction-reduced water to clear acid was 6 : 4, the surfaces of the fractures can be itched away, thereby increasing the conductivity of the fractures and strengthening the seepage channels. A clear thickening agent with acid tolerance and high friction-reducing capacity was selected and used to formulate a clear acid with percent friction reduction of 63.5%. With this acid, the friction of acid fracturing operation was effectively reduced, which is beneficial to high flow rate acid fracturing job. At closure pressure of 30 MPa, the conductivity of the acid-itched fractures reached 14.9 μm²∙cm. The rocks, after being itched by the clear acid, had basically unform surface structures. The acid-itched wormholes and the surfaces of the factures are free of any attachment, which is less damaging to the reservoirs. This acid was used in the fracturing of the well FM1HF. Using a Φ12 mm choke, the daily gas production rate of the well reached 4.12 × 10⁴ m³, a stable industrial gas production rate first obtained from the Maokou formation in southeast Sichuan, which proves the feasibility of this fracturing technology in stimulating marl reservoirs. This technology will provide a good reference and popularization value for stimulating similar reservoirs in China.