Analysis of Petrophysical Properties and Evaluation of Gas Flood Possibilities for Chinese Tight Sandstone Using Pore Network Modelling

Abstract

Abstract Hydrocarbon recovery from conventional resources has seen a great decline over the years, with the most recently discovered reservoir being from unconventional resources. Unconventional resources (such as tight oil, shale gas, tight gas, etc.) have contributed immensely towards the world energy provision and continual technical development to best understand and predict the best recovery method that is affordable has been the oil and gas industry focus. Relative permeabilities and capillary pressures of tight sandstone have proven to be one of the governing parameters important in understanding fluid flow through the tight reservoirs and estimating the recoverable hydrocarbon. Estimation of these petrophysical properties (especially three-phase properties) is tedious and costly using convention experimental method and thus the advent of pore network modeling which offers competitive alternatives in terms of accuracy, time, and cost. In this paper, we present the use of pore network modeling to analyze the petrophysical properties and evaluate possibilities of gas injection for the Chinese tight sandstone sample. Two segmented micro-CT images S5 and S9 were obtained from a Chinese tight sandstone reservoir and the network extraction was carried out using Heriot-Watt university in-house PAT software. The pore network model takes as input the extracted network of the two tight sandstone samples and simulations were carried out to determine and analyze the two-phase petrophysical properties of S5 and S9 considering different wettability scenarios. Three-phase displacement was also carried out for S9 to estimate petrophysical properties for the gas flooding process. The comparison of mercury drainage curve and single-phase properties (i.e. porosity and permeability) of the sample S9 from an experiment with network model derived ones show close similarity in the porosity and permeability value. Additionally, sensitivity for the three-phase displacement of the sample S9 has been conducted on residual oil saturation for different wettability conditions, different target water flood saturation, and spreading and non-spreading oil. For spreading oil, which is more desirable for enhanced oil recovery, residual oil decreases with decreasing target waterflood saturation. This shows that the pore network model can be successfully used to analyze petrophysical properties of corresponding tight sandstone formation as well as predicts the most suitable flooding mechanism.