Experimental study and numerical simulation of hydraulic fracturing tight sandstone reservoirs

摘要

Unconventional tight sandstone reservoirs have been developed during recent years and a large number of multi-stage fractured horizontal wells have been drilled to stimulate reservoir performance. However, fluid flow in low permeability porous media no longer obeys Darcy's law and instead conforms to low-velocity non-Darcy flow. Most commercial numerical simulation software for multi-stage fractured horizontal well development may cause inaccuracy in simulating performance of tight sandstone reservoirs. In this paper, the investigation of existing conditions of low velocity non-Darcy flow for oil flow in irreducible water saturation tight sandstone cores was conducted and discussed through lab-experiments. And existence of low velocity non-Darcy flow was proven. Then, based on the low velocity non-Darcy flow model, the multistage fractured horizontal well numerical simulator was developed and verified. The comprehensive comparison and analysis of the simulation results of Darcy flow and non-Darcy flow were presented including liquid production rate, oil production rate, water cut, reservoir pressure, oil saturation distribution, and dimensionless permeability coefficient. With considering the non-Darcy flow, the fluid flow in reservoir consumes more driving energy and the water flooding efficiency was reduced. Finally, a multistage fractured horizontal well water injection pilot test in Fan-116 block was analyzed to perform the non-Darcy flow numerical study on an actual tight sandstone reservoir. The results show that for the tight sandstone reservoir, the optimal water injection time is when the average reservoir pressure declined to 26.92 MPa based on maximizing the total field oil production in 15 years. This pressure level is close to the hydrostatic pressure and the optimized recovery is 20.51% in the final simulation time. This approach is an initial exploration for the "multi-stage fractured horizontal well development for tight sandstone reservoirs considering non-Darcy flow'' and could be applied to other tight oil/gas reservoirs. (C) 2015 Elsevier Ltd. All rights reserved.