A new evaluation method for recoverable reserves of water-bearing tight sandstone gas reservoir and its application

The determination of recoverable reserves is the core work of gas reservoir development evaluation, and provides an important basis for scientifically making development program. The tight sandstone gas reservoirs generally have the characteristics of compact matrix and high water saturation. In the eary developent stage of gas reserviors, it is a great challenge to accurately evaluate the reserve in matrix due to the very slow recovery process. According to the characteristics of pressure drop funnel during gas reservoir depletion production, the physical simulation experiment method of long-core multi-point pressure measurement is used to determine the variation charateristics of pore pressure in water-bearing reservoirs with the conventional air permeability of 1.63, 0.58, 0.175 and 0.063 mD, respectively. On this basis, this paper establishes a set of area-proportion methods, realizes the quantitative evaluation of recoverable reserves, and proposes measures and suggestions for improving gas reservior utilization technologies. In case of the well control range of 400 m, the evalution is perfromed on reserve utilizaiton in the condition of the maximum degree of reserve recovery and the initial production allocation with the instantaneous gas production decreased to 10%, respectively. The results show that the recovery degree of water-bearing tight sandstone gas reservoirs is closely realted with reservoir permeability, water saturation and abandonment production. As a whole, the more compact the matrix, the higher the water saturation and the abandonment production, the lower the recovery degree of reservoirs; it can be increased by optimizing the matching relationship between well pattern infilling, proportion of artificial fractures and the matrix, water-control mining to increase gas production while avoiding movable water layers, reducing abandonment production, and prolonging the life cycle of gas wells. © 2021, Editorial Office of ACTA PETROLEI SINICA. All right reserved.