Research On Percolation Mechanism Of Tight Sandstone Gas Reservoir

The world energy evolution shows that the development and utilization of natural gas is the trend in today's world, with the progress of science and technology, and the increasing requirements of environmental protection, the status of natural gas will continue to improve. Since 2000, the production of Chinese tight sandstone gas reservoir increases rapidly. It is estimated that the production of tight sandstone gas production will account for more than 30% in 2020. Therefore, the tight sandstone gas reservoir is one of the most important areas of Chinese natural gas reserves and production in the future. However, this kind of reservoir have the characteristics of complex rock pore structure, complicated gas reservoir relationship between gas and water low permeability, high water saturation, and poor quality reserves. The production process showed a low single well gas production, gas production with water, low producing degree of reserves and recovery problem. Which needs to strengthen the research of reservoir seepage mechanism urgently, and lay the theoretical foundation for improving the yield of single well and gas recovery, to provide technical support for the benefit of development. In this paper, based on a large number of researches at home and abroad that are similar with gas reservoir geology and the characteristics of exploitation, importantly facing on the technical problems in production, taking the Sulige gas field as the main research object, using high pressure mercury penetration, casting slice, gas water phase seep,nuclear magnetic resonance, gas reservoir development physical simulation and numerical simulation and other experimental techniques, dynamic production analysis,guided by petrology, oil and gas reservoir fluid mechanics in porous medium and gas reservoir engineering. Deepen the study of Chinese tight sandstone gas reservoirs rock micro pore throat structure and physical property characteristic, the gas and water flow law in sandstone rock micro pore throat, study on the mechanism of tight sandstone gas reservoirs. The main results are as follows:(1)Quantitative evaluation of different permeability sandstone micro pore throat structure characteristics, recognized that fluid seepage channel with radius of less than 0.1 M is main in the tight sand, the proportion of the total pore throat can reach 60 ~ 80%,playing an important role in the control of rock permeability. Pore throat is more than 0.1 M accounted for only 20 to 40% of total pore throat, established of a micro pore structure model, laid the foundation for the mechanism of gas and water seepage researches.(2)Understanding the process of gas drive water filling into the reservoir include gas saturation(Sg),reservoir pressure(P) and reservoir permeability(K) change rule, the fitting the empirical calculation formula of gas saturation, taking Sulige gas field in Ordos Basin as an example, through experimental tests, anysis from cores and compared with the empirical formula calculation results, and established of gas saturation and reservoir permeability relation chart, providing a guidance for low permeability tight sandstone gas reservoir including gas quality evaluation.(3)Studied systematically the characteristics and laws of water phase, gas phase and gas water two-phase flow of tight sand,understanding of the micro pore throat of gas and water seepage mechanism is preferred, the distribution patterns of four kinds of residual water in the pore throat of sandstone are established, developed the Darcy flow equation with starting pressure,formed the evaluation of matrix seepage ability and the stable contribution chart, provide the basis for the rational foundation of gas production.(4)Establishing the relationship between pore pressure and core length function(P ~ L function),formed the relationship plate chard drainage radius and formation pressure, defined the drainage radius of the tight sandstone reservoir in different water conditions, providing a reference for similar gas reserves mobility evaluation, early development well network deployment and the development of late well spacing optimization encryption.(5)Evaluating the reservoir permeability, water saturation, production proration and abandonment pressure, vertical heterogeneity and plane heterogeneity(being resistance flow zone and plane employ range in reservoir sand body) and other factors to the low permeability of tight sandstone gas reservoir recovery effect, which indicates the direction for the further improvement of gas reservoir recovery.