No abstract

Gas-water relative permeability was tested in the full diameter cores of three types of reservoirs (matrix pore, fracture and solution pore) in Gaoshiti-Moxi block under high pressure and temperature to analyze features of their gas-water relative permeability curves and gas well inflow dynamics. The standard plates of gas-water two-phase relative permeability curves of these types reservoirs were formed after normalization of experimental data. Based on the seepage characteristics of fractured reservoirs, the calibration methods of gas-water two-phase relative permeability curves were proposed and the corresponding plates were corrected. The gas-water two-phase IPR (inflow performance relationship) curves in different type reservoirs were calculated using the standard plates and validated by the actual performances of gas wells respectively. The results show that: water saturations at gas-water relative permeability equal points of studied reservoirs are over 70%, indicating strong hydrophilic; the dissolved cave type has the biggest gas-water infiltration interval and efficiency of water displacement by gas, followed by the matrix pore type and then fractured type; and the fractured type has the highest the permeability recovery degree, followed by the dissolved cave type and then matrix pore type. The calibrated gas-water two-phase relative permeability curves of fractured carbonate reservoirs can better reflect the gas-water two-phase seepage law of actual gas reservoirs and the standard plates can be used in the engineering calculation of various gas reservoirs. The characteristics of calculated IPR curves are consistent with the performance of actual producing wells, and are adaptable to guide production proration and performance analysis of gas wells.

Water invasion in carbonate gas reservoirs often results in excessive water production, which limits the economic life of gas wells. This is influenced by reservoir properties and production parameters, such as aquifer, fracture, permeability and production rate. In this study, seven full diameter core samples with dissolved pores and fractures were designed and an experimental system of water invasion in gas reservoirs with edge and bottom aquifers was established to simulate the process of water invasion. Then the effects of the related reservoir properties and production parameters were investigated. The results show that the edge and bottom aquifers supply the energy for gas reservoirs with dissolved pores, which delays the decline of bottom-hole pressure. The high water aquifer defers the decline of water invasion in the early stage while the big gas production rate accelerates water influx in gas reservoirs. The existence of fractures increases the discharge area of gas reservoirs and the small water influx can result in a substantial decline in recovery factor. With the increase of permeability, gas production rate has less influence on recovery factor. These results can provide insights into a better understanding of water invasion and the effects of reservoir properties and production parameters so as to optimize the production in carbonate gas reservoirs.