Large Cattle To Gas Reservoir Seepage Characteristics Of Experimental Low-speed Single Well Numerical Simulation

These years, as the developing of low-permeability gas reservoirs, researches on low-permeability gas reservoirs' percolation rule become more and more important. Low-permeability and extra low-permeability gas reservoirs have many characteristics that conventional gas reservoirs do not have, such as complicated and diverse pore structures, winding and tortuous throats, low porosity and low permeability, high water saturation, these characteristics result gas's non-linear flow features.Up to now, though investigations on mechanism experiment and theoretical model have been made some progress, the investigation on threshold pressure gradient of low-permeability gas reservoirs with irreducible water is very limited and there are still debates. Therefore, this thesis conducts a series of studies on Huabei Daniudi gas reservoir aiming at the issue of gas percolation features in low-permeability gas reservoirs with irreducible water, studies completed include reservoir characteristic experiments, low rate flow experiments, percolation mathematical model establishing and resoling, program developing, single well numerical simulation. Major outcomes and conclusions achieved are following:(1) Numerous experiments on reservoir characteristics are conducted, including petrophysical parameter measurement, thin section, scanning electron microscope analysis and mercury penetration experiment; experimental results indicate that Daniudi gas reservoir is a low-porosity, low-permeability and tight gas reservoir;(2) The low rate flow experimental apparatus is modified and non-Darcy percolation experiments at low rate are accomplished, experimental results indicate that there is the threshold pressure gradient in Daniudi gas reservoir;(3) The threshold pressure gradient of each rock sample is figured out by mathematical method, the relation between threshold pressure gradient and permeability is established;(4) A three-dimension and two-phase percolation mathematical model with considering the threshold pressure gradient is established, finite difference equations are deduced by numerical dispersing, the threshold pressure gradient of each grid is different from each other and is determined by initialization;(5) A simulation program is developed by the Fortran 90 language, simulation results from the new simulator without considering threshold pressure gradients agree well with which calculated by a business software;(6) Single well numerical simulation results demonstrates that the threshold pressure gradient will affect the distribution of formation pressure and production performance of a gas well, the maldistribution of threshold pressure gradients will also cause the difference of formation pressure distribution. Therefore, with considering threshold pressure gradients and the maldistribution of threshold pressure gradients caused by reservoir heterogeneity, it will be more objective and better to forecast the production performance of gas wells and guide low-permeability gas reservoirs' practical production.