Study on Prediction Model for Unsteady Water Influx Rate and Dynamic Reserves of Gas Reservoirs with Bottom Water

doi:10.3969/j.issn.1006-6535.2023.02.016

Abstract

Abstract: The V-H model is generally adopted to predict the unsteady water influx rate of gas reservoirs with bottom water, with the water seepage direction assumed as the planar radial flow, which is inconsistent with the vertical seepage characteristics of gas reservoirs with bottom water, leading to a deviation in the prediction of water influx rate and dynamic reserves. To solve this problem, a model for calculating the unsteady water influx rate of gas reservoirs with bottom water was established with consideration of the vertical flow of bottom water and the dimensionless aquifer thickness. By solving the water influx rate through numerical inversion, an empirical equation for the unsteady water influx rate of gas reservoir with bottom water was regressed. Coupled with the material balance equation, a method was developed to work out the dynamic reserves of gas reservoirs with bottom water. It is found in the study that the dimensionless aquifer thickness has a significant impact on the water influx rate. If the dimensionless aquifer thickness is small, the water influx flows linearly first and then radially, and the predicted water influx rate is greater than that of the V-H model. If the dimensionless aquifer thickness is large, the water influx flows hemispherically, and the predicted water influx rate is smaller than that of the V-H model. The study results were applied to the anticlinal gas reservoir with bottom water in H4 Fault Block, BD Gas Field, the East China Sea. The results show that the new method is faster than that of edge water model in predicting the bottom water influx rate, and the fitting effect of the predicted pressure is better than the V-H model, which is more consistent with the actual characteristics of water invasion in the gas reservoirs with bottom water. The study results are of great significance to improve the calculation accuracy of dynamic reserves of gas reservoirs with bottom water.

Key words: gas reservoir with bottom water, unsteady water, hemispherical flow, water influx rate, dynamic reserve

CLC Number:

TE349

Li Yuansheng, Teng Sainan. Study on Prediction Model for Unsteady Water Influx Rate and Dynamic Reserves of Gas Reservoirs with Bottom Water[J]. Special Oil & Gas Reservoirs, 2023, 30(2): 116-121.

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