Study On Influence Mechanism Of Recovery In Tight Sandstone Gas Reservoir

Through the method which combines physical simulation experiment and numerical calculation the gas reservoir engineering for difficult producing and low recovery efficiency based on Anyue Xu 2 tight gas reservoir as the research object. Characteristics which influence the gas reservoir recovery were found and form a complete set of tight sandstone gas reservoir reasonably to improve recovery efficiency development program evaluation system. The main research results as followings:(1) The pore throat of Anyue Xu 2 are not developed, with sub-micron pore throat obtained mainly. Effective pore throat radius are mainly distributed in the range of 0.07～2μm microns. Pore types are mainly intergranular pore between grains. Pelitic impurity, authigenic clay minerals and organic matter are not evenly distributed in the intergranular due to poor pore connectivity between them. The pore structure is characterized by tight sandstone gas reservoir seepage resistance、poor development、low recovery efficiency.(2) Tight gas reservoir is limited by high abandonment formation pressure and small pore throat radius. In the process of gas reservoir engineering calculation can ignore the slippage effect and high speed non-Darcy seepage influence on the recovery factor. There is large threshold pressure gradient and strong stress sensitivity is in reservoir. These two kinds of seepage law sharply reduced the gas reservoir recovery efficiency. By fitting a lot of experiment data gas reservoir engineering calculation method is established for threshold pressure gradient and stress sensitive.(3) Through physical simulation experiment and numerical calculation method of combining the gas reservoir engineering. Seven factors such as specific permeability have a significant effect on gas reservoir recovery efficiency. Recovery and permeability、water saturation、heterogeneity variation coefficient and discharge radius components function relationship. Also with the original formation pressure and the thickness of the reservoir as logarithmic function relationship. And with abandoned bottom well pressure as linear function relation. The influence degree of the seven factors of recovery efficiency respectively:26.45%、 10.03%、12.58%、12.23%、21.29%、14.46%、3.04%.(4) Use the method of fuzzy mathematics, influence factors of gas reservoir was analyzed and a method for comprehensive evaluation of the multi parameters of tight sandstone gas reservoir recovery was established. Parameter selection takes into account both the static reservoir control factors, but also takes into account the dynamic laws of seepage with production development, recovery rate of comprehensive evaluation value and the deviation of the gas field production dynamic data basically no more than 5%, is more objective and reasonable evaluation system.(5) The gas reservoir recovery-capillary number model was established. This model can indicate the gas reservoir recovery mechanism:gas reservoir recovery is a ratio that efficiency of exhaustion with single well limit production of economic and leakage flow coefficient. If efficiency of exhaustion is more quickly, single well limit production of economic or leakage flow coefficient is smaller, then gas reservoir recovery is bigger.(6) Use the capillary number model of gas reservoir recovery efficiency to calculate the capillary number of the typical tight sandstone gas reservoir in US. Clear the applicable conditions of large-scale hydraulic fracturing technology that the thickness of single sandstone layer should more than 20 meters thick and the capillary number should greater than 10 after conventional fracturing. Clear the applicable conditions of well pattern infilling technology, the original water saturation of reservoirs should less than 60% and the capillary number should greater than 1014 after conventional fracturing.