Water Intrusion Dynamic Analysis And Reserve Calculation Of W Water Drive Gas Reservoir

In terms of water drive gas reservoirs, the water invasion has dual effects on gas reservoir productions. In helpful ways, water invading into gas reservoirs will become one kind of driving energy; however, in harmful ways, wellbore frictional resistance increases, but gas reservoir production decreases. Finally, it results in the decline of gas recovery rate. Therefore, the studies of water invasion performance in water drive gas reservoirs have significance on the exploitation of water drive gas reservoirs.Based on a large number of literature research, water invasion performance and calculation of reserves are lucubrated in this paper, mainly focusing on the following.(1) Conducting research on the mechanism of water invasion as well as the source and regularity of produced water of gas reservoirs. Analysising the principles, procedures, advantages and disadvantages of the methods of how to identify early water invasion in water drives gas reservoirs.(2) Studying the method of calculating bottom hole flowing pressure through well reservoir pressure; Improving the calculation method of single well reservoir pressure depending on flowing material balance method with its through; Presenting an improved flowing material balance method when water invasions happened. When the water invasion, bottom hole flowing pressure will be influenced and change slowing down, then the same changing trend between with the bottom hole flowing pressure and the pressure of PH; according to this we can slove the formation pressure.(3) Summarizing several ways of calculating average formation pressure, based on the single well formation pressure; After solving out the formation pressure of a gas reservoirs, the dynamic method will be applied to estimate the size of water body in gas reservoirs, with the establishment of the material balance equation. Analysising several classic models for water influx calculation, and make a study of calculating water influx through the traditional reserves method and improved flowing material balance method.(4) According to the volume balance principle, the model of estimating water breakthrough time has been deliberated. Combination of both pressure drop equation and Quasi steady state model use the two iteration method forecast the pressure and water influx of gas reservoir at different time; then according to deliverability equation slove the bottom hole flowing pressure, finally make out the water body advancing distance.The formula predicting water breakthrough time of gas well in bottom water drive is derived.(5) Using water influx curve to study gas reservoir and revising some water influx curves, where straight line do not exist. Combining water drives gas reservoir material balance equation with unstable water influx calculation model, in order to build up water drive gas reservoir reserves calculation model based on improved material balance equation. Conducting research on calculating the reserves of water drive gas reservoir based on an virtual curve method.(6) In a calculation example, a gas reservoir called "W" has been estimated to check whether water invasion happened or not by both traditional reserves method and dynamic production data. Additionally the water invasion models are determined and the water production conditions of gas reservoirs are classified. Calculated the average formation pressure of gas reservoir W based on both flowing material balance method and improved flowing material balance method, and obtain the water body size of this gas reservoir by applying dynamic method, and then, computed cumulative water influx of gas reservoir W, employing improved flowing material balance method and traditional reserves method. Estimate the water breakthrough time of this gas reservoir through different exploitation rates. Calculate the reserves of "W" by lot of methods. After that, make a comparison of these results in order to prove the reliability of the improved flowing material balance method. Finally, calculate the workable reserve of gas reservoir W utilizing virtual curve method.Through the above work, a set of methods has been conducted for water-drive gas reservoir, and it provides theoretical foundation of rational exploitation of gas reservoirs.