Application of Fracture Propagation and Production Simulation Technology to Multi-Stage Length Optimisation in Horizontal Wells

Abstract

Low-permeability reservoirs are characterized by low oil and gas abundance, poor permeability, natural productivity lower than the lower limit of industrial oil flow, and rapid decline of formation energy. Hydraulic fracturing technology is widely used for the development of low-porosity and low-permeability reservoirs. The hydraulic fractures formed by using the hydraulic fracturing technology are the "underground highway" for oil and gas flowing from the deep reservoir to the wellbore. The combination between the long well section of the horizontal well in the reservoir and the wellbore can greatly improve the utilization of oil and gas resources in the reservoir. Therefore, hydraulic fracturing is the key technology to improve the production of low-permeability reservoirs. This paper establishes a volume fracturing propagation model by using the finite element method and discrete element method, and conducts the fracture propagation simulation of multi cluster fracturing in horizontal wells of low-permeability Nanyishan reservoirs in Qinghai Oilfield. The results show that when the stress difference（Difference between the maximum horizontal principal stress and the minimum horizontal principal stress） is less than 4 MPa, volume cracks tend to be generated. When the stress difference is higher than 5 MPa, plane cracks are mainly generated. The natural fracture density affects the volume fracturing effect only under the condition of low stress difference. When the stress difference is 3 MPa, the number of perforating clusters is increased, the cluster spacing is reduced, the improvement area is not significantly increased, the cracks between clusters are seriously interfered, and local cracks are merged. When the stress difference is 5 MPa, there is relatively weak interference between clusters. The increase of perforation clusters promotes the communication between natural fractures, volume fracture development, and expansion of reconstruction area. The research results of this paper provide strong technical support for optimizing the fracturing scheme, improving the single well productivity of low-permeability reservoirs, and developing low-permeability reservoirs in a cost-effective way.