Naturally fractured-vuggy carbonate gas condensate reservoirs in China have some distinctive characteristics: deep buried depth, multi-scale fractures, vugs and caves developed, poor reservoir connectivity and high production decline rate. It is hard to build effective geological models and run reservoir simulation for production forecasting. So how to properly forecast the performance of this kind of reservoirs is a major challenge. This paper presents a systematic technique of production forecast to solve this problem.

The systematic technique mainly involves analytical and numerical production analysis (PA), analytical and numerical pressure transient analysis (PTA) and material balance analysis in combination with the geological analysis results. Firstly, using the analytical PA and PTA can quickly and correctly evaluate reservoir properties. Take Tazhong No.1 carbonate gas condensate reservoir in China for example to elaborate the details of this method. The results show that the systematic method can not only properly calculate the reservoir properties, but also can quickly and properly forecast reservoir performance of fractured vuggy carbonate gas condensate reservoirs. And the calibrated dynamic numerical model can both match well production history data and well pressure data. Examples are presented to show how these material balance analysis, analytical and numerical PA and PTA methods fully integrated and constrained with each other, and how the reliable results can be generated finally. Because of the poor connectivity characteristic of Tazhong No. 1 field, dynamic models for each fractured-caved unit should be built and applied for performance prediction.

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