Matrix-fracture coupling flow model of long-crack fracturing vertical well in tight oil reservoirs

Long-crack fracturing pressure behavior and production change laws of tight oil reservoirs have not been clarified clearly, and the development scheme is designed without the guidance of theoretical model. To deal with the matrix-fracture combined flow of long-crack fracturing, this paper established a matrix-fracture combined flow model of long-crack fracturing vertical well which considers the influences of threshold reservoir pressure gradient and intra-fracture high speed non-Darcy flow. Then, it was solved by means of Laplace transformation, point source function and Stehest numerical inversion. Finally, the pressure respond behaviors of long-crack fracturing well in tight oil reservoirs and their influential factors were determined. It is indicated that dimensionless pressure and pressure derivative increase with the increase of threshold pressure gradient, but the influence of threshold pressure gradient on dimensionless pressure and pressure derivative is less in the early stage and greater in the late stage. Non-Darcy flow coefficient has greater influence on dimensionless pressure and pressure derivative in the early stage. And with the increase of non-Darcy flow coefficient, dimensionless pressure and pressure derivative increase. The higher the non-Darcy flow coefficient of fracture is, the lower the production rate of fracturing well is and the shorter the optimal half fracture length of fracturing well is. The research results provide the theoretical guidance for long-crack fracturing scheme design and well test analysis of tight oil reservoir.