A Systematic Dynamic Characterization Method for Abnormally High-Pressured Gas Reservoirs

Abstract

Compared to the normal clastic gas reservoirs, abnormally high-pressured gas reservoirs in China have some distinctive characteristics: deeper buried depth, higher productivity of single well, more heterogeneous formation, stress sensitive rock and more difficult to develop. It's not feasible to identify and characterize this kind of reservoirs only based on one method. This paper presents a systematic method of dynamic characterization for abnormally high-pressured gas reservoirs, which mainly involves material balance analysis, rate transient analysis and well test interpretation in combination with geological analysis results.This paper firstly establishes a new equation suitable for abnormally high-pressured gas reservoir with aquifer support. Then the systematic method mainly using material balance analysis, rate transient analysis and well test analysis are detailed presented. The systematic method can fully integrate the long-term low accuracy data of dynamic production and short-term high-precision data of transient well testing. And the three methods can be combined and constrained to each other, in order to correctly evaluate well and reservoir properties, such as the formation permeability, well skin, oil drainage radius, gas in place and so on. Also the methods have the diagnostic function to aquifer influx, which can predict water breakthrough in gas wells. Furthermore, based on the evaluation results, the Љdynamic numeric modelЉ can be built and all three methods can be used to predict the performance of the wells.M1 abnormally pressured gas filed in China is taken as an example to elaborate the details of this method. The calculated well drainage radius shows that some well production is interfered by surrounding wells, while some wells are not. Also transmissibility of faults are evaluated and used in the numerical model building. Based on the evaluated properties, Љdynamic numerical modelЉ of the gas reservoir are established and applied to the well performance prediction, which are validated by actual gas well performance. It can be seen that these three methods are fully integrated and constrained with each other, which can generate a reliable result.This systematic technique has been successfully applied to ЉM1 gas field Adjustment and Optimization PlanЉ, which provides a reliable foundation for the effective development of M1 gas field. Furthermore, the systematic method can be used for reservoir evaluation and performance prediction in any other abnormally pressured gas fields.