Study On Oil Recovery And Recovery Of Y Gas Reservoir

The recovery has been widely studied all over the world. Y gas reservoir is integrated with reservoir geology, mechanics of fluid flow in porous media, natural gas engineering and a laboratory experiment in this dissertation. The residual gas mechanism, residual gas saturation testing experiments, formation pressure analysis, influx calculation, dynamic reserves computation, aquifer activity level calssification, volumetric sweep efficiency calculation and prediction, and recovery plate of water-drive gas reservoir at abandont wellhead pressures, were studied. Major work and outcomes are shown as following:(1) Y gas reservoir is in mid-to later production period currently, the water invasion influence on single well productivity is serious, so it is necessary to study recovery in the. depressuring production.(2) Micro and macro mechanisms of residual gas were analyzed. Black Stone I co-current imbibition device was adopted to test residual gas saturations of20cores from Y gas reservoir. The analysis of the effects of porosity and permeability on maximum residual gas saturation showed that as porosity and permeability increased the maximum residual gas saturations increased also, a mathematical relationship between the original and residual gas saturation was established, which was applied to calculate the residual gas saturation of Y gas reservoir.(3) A method which can be used to analyze the formation pressure of single well was proposed. The results showed that the formation pressure of gas wells in the Y gas reservoir was identical with field test results. Then the average area weighted method was adopted to calculate the formation pressure of the whole Y gas reservoir.(4) Aquifers were classified according to different conditions. The identification methods of water invasion of gas reservoirs were described, and the water influx of Y gas reservoir was calculated based on Fetcovich model.(5) Dynamic reserve of Y gas reservoir was taken into account on the base of the material balance equation of water-drive gas reservoir. The activity level of aquifer in Y gas reservoir was determined according the Lunyou Zhang’s aquifer level activity judgment equation. The current volumetric sweep efficiencies of Y gas reservoir were computed using Stoian’s formula. And then, the volumetric sweep efficiency at abandont wellhead pressure was predicted. When abandon well wellhead pressure of2.0MPa,1.38MPa and0.69MPa, volumetric sweep efficiencis were0.6128,0.6496and0.6617, respectively.(6) Agarwal’s dimensionless endpoint equation was integrated with Lunyou Zhang’s aquifer level activity judgment equation; the recovery plate at abandont wellhead pressures in depressurizing production period was established. The average recoveries at the abandont wellhead pressures of2.0MPa,1.38MPa and0.69MPa were73.15%,74.37%and74.80%, respectively. Then remained reserves of Y gas reservoir were atained.In this dissertation, the theory of recovery of water-drive gas reservoir in the depressurizing production were formed, which includes residual gas study, formation pressure computation, invasion study, dynamic reserve computation, aquifer activity level judgment and volumetric sweep efficiency calculation. This theory not only can provide a theoretical basis for adjusting the development strategies in mid-to later periods of Y gas reservoir that relevent appropriate production measures can be taken in time, but also it can be used to guide the development activities of similar water-drive gas reservoirs.