Daobing Wang

Well spacing design for low and ultra-low permeability reservoirs developed by hydraulic fracturing

Abstract In order to simulate non-Darcy flows in low and ultra-low permeability reservoirs, based on the black oil simulator, a three-dimensional, two-phase model was established considering two-phase start-up pressure, permeability sensibility and fracture conductivity decline. Then numerous simulations were run to analyze the elliptic drainage area induced by a fractured well, the results show that: for water fractured well, permeability is the dominant factor affecting the elliptic drainage area at the beginning, and pressure difference and start-up pressure have increasing effects as time goes by. However, no factor has a marked impact on the shape of elliptic drainage area. Parameters of elliptic drainage area can be calculated with GA-BP neural network improved by genetic algorithm. Aiming at acquiring maximum sweep efficiency, well spacing equations were deduced for rectangular pattern and diamond inverted nine-spot pattern. Field application demonstrated daily oil production enhanced 1.25 times after hydraulic fracturing, and the long time stimulation effect is substantial.

Evaluations of Fracture Injection Pressure and Fracture Mouth Width during Separate-Layer Fracturing with Temporary Plugging

Separate-layer fracturing with temporary plugging (SLFTP) is a potential way to stimulate multiple layer reservoirs due to its low cost, low risk, and high efficiency. In this study, based on the cohesive zone model (CZM), a 3D fully fluid-solid coupling and multiple layer model is established to investigate factors influencing fracture injection pressure and fracture mouth width. The cohesive layer properties are based on the reported study, which have been validated through a series of numerical experiments. Innovatively, the spring model is innovatively proposed to represent the plugging effect of diverting agents and prop the aperture of the previous fractures. Simulation results reveal that the effects of previous fractures in multiple layer formations can be neglected, which is quite different from multistage fracturing for horizontal wells. Fracture injection pressure can be evaluated more accurately by taking the following factors into consideration: the minimum horizontal principal stress, rock tensile strength, injection rate, and pore pressure enhancement. Further, fracture mouth width is strongly influenced by rock tensile strength, Young’s modulus, and injection rate. This study provides a guidance for candidate well selection and diverting agent optimization during SLFTP in multilayer formations.

The main factors and rules of stress shadow of perpendicular cracks

Based on elasticity theory, we use numerical Galerkin finite element discretization method and implement Matlab finite element code to simulate “stress shadow” distributions of mutual orthogonal fractures. The principal stress and principal distributions have the symmetry characteristic on the intersection (coordinate origin). The relationships between stress shadow and flow pressure ratio, pore pressure, fluid pressure and horizontal stress contract are analyzed, respectively. By these techniques of variable displacement construction, changing the viscosity of the fracturing fluid, exploitation of oil and gas wells changing pump rate and fracturing fluid viscosity, reducing pore pressure and increasing the injection volume, taking the advantages of shadow effect, it is likely to produce a complex fracture network.