Abstract: Because of low-permeability property, horizontal well multi-stage fracturing technology is widely used to improve oil well production, and achieve economic value, such as tight and low-permeability oil and gas reservoirs. Based on the seepage mechanics, a mathematical model of multi-stage fractured horizontal well is stablished with consideration of stress sensitivity and varying conductivity. The model is solved by employing Laplace and Fourier integral transformation, pressure drop superposition principle and fracture discrete coupling method in Laplace domain. The Stehfest numerical inversion algorithm is used to calculate dimensionless wellbore pressure in real space and dimensionless pressure and its derivative log-log curve is drawn. The results show that if hydraulic fracture conductivity located at wellbore end-node fracture is higher than that of hydraulic fracture located at wellbore middle fracture, dimensionless pressure curve is lower during early bilinear flow and linear flow stage and production pressure difference is smaller. When the dimensionless conductivity decreases along the direction of the hydraulic fracture, the bigger the gradient is, the higher the dimensionless pressure curve is during the early stage, and the bigger the production pressure difference is. The larger the stress sensitive coefficient, the larger the creep amplitude of the dimensionless pressure and its derivative curve; the smaller the reservoir-capacity ratio, the earlier the cross-flow occurs, the longer the cross-flow duration. The larger the cross-flow coefficient, the earlier the channeling occurs. The results can provide guidance for well test data interpretation in fractured reservoirs.

Key words: shale oil reservoirs, multi-stage fractured horizontal well, well test analysis, varying conductivity, stress sensitivity