(568c) Experiments and Simulations for Evaluating Relative Flow of Gas and Water in Tight Gas Reservoirs

Tight gas reservoirs refer to gas reservoirs with very low permeability to gas phase. The permeability is usually less than 0.01 mD and most of the times are in the microdarcy range. Current US consumption of natural gas is around 25 tcf (trillion cubic feet), and about 10 % of the gas is produced from tight gas reserves. Proved tight continuous gas reserves have been estimated by the U.S. Geological Survey at 308.1 tcf, within a range of 219.4 to 416.6 tcf. An independent study estimated the total tight gas reserves in Wyoming state alone to be around 15000 tcf. This just confirms the enormous amount of energy resource trapped in tight gas reservoirs. Recovery from tight gas is very difficult because of low permeability and requires extensive fracturing to get economical rates of gas recovery. The current high oil and gas prices make recovery from tight gas reserves economical. One of the main issues with tight gas reserves is the uncertainty and long time of measurement associated with the measure of the reservoir permeability. If a conventional steady state method is to be used to measure the permeability of tight core, it might take days or even weeks to reach steady state and evaluate the permeability. In the current work we evaluate a different technique of using a pulse decay unsteady state method to evaluate permeability of tight reservoir rocks. A novel experimental technique has been developed to saturate the tight gas core to different water saturations and measure the gas phase relative permeability. This is the first time a method has been developed to measure relative permeability of gas for tight gas reservoirs. The measure of relative permeability is of great importance in evaluating the economic success of the process of gas recovery from tight gas reservoirs. In this study, we use pulse decay technique to measure the absolute permeability of the tight gas rocks and then analyze the data by numerical simulation. We find that the relative permeability and absolute permeability of a tight gas core can be evaluated in a day compared to weeks and months required earlier to obtain the same data.