An Integrated Dynamic Characterization and Performance Prediction Method for Fractured-Vuggy Carbonate Reservoirs
Authors: Yong Li , Baozhu Li , Hui Peng , Fangfang Chen 
Published: November 2016

Naturally fractured-vuggy carbonate reservoirs in China have some distinctive characteristics: deep buried depth, multi-scale fractures, vugs and caves developed, poor reservoir connectivity and isolated developed reservoirs with small volumetric volume. It is hard to build effective geological models and run reservoir simulation for production forecasting. So how to properly characterize and forecast the performance of this kind of reservoirs is a major challenge. This paper presents an integrated dynamic characterization method to solve this problem.

The workflow of the integrated dynamic characterization method are presented. The method mainly involves analytical and numerical production data analysis (PA) and well test analysis. Firstly, based on seismic interpretation and attribute imaging, reservoirs are divided into many different flow units, with reserves and boundaries of each unit determined. Then for each unit, analytical rate transient analysis and analytical pressure transient analysis are applied to calculate original oil in place (OOIP), permeability, etc. After that, numerical production data analysis are used and numerical dynamic model are calibrated with analytical analysis results constrained. Finally, numerical well test analysis models are established and calibrated, which initialized from numerical production data analysis models.

This new method has been applied on K fractured-vuggy carbonate reservoir in China. The mid-depth of K reservoir is 6500m with primary depletion currently, and current oil recovery is only around 7% of OOIP with more than 100 producers. Based on seismic modeling study, K reservoir is divided into different flow units, which are thought to be isolated and have no pressure communication from each other. Then how to use the proposed integrated method to characterize flow units are detailed illustrated with the explanation of the application sequence of different analysis method, especially how to combine and constrain these analytical and numerical methods with each other until reliable results generated are detailed presented. Through the dynamic characterization of K reservoir with seismic and geological understanding integrated, reservoir properties of each units are correctly calibrated and evaluated, which includes flow boundary, permeability, well skin, oil in place and so on. Furthermore, the connectivity among different flow units are revised and calibrated based on dynamic characterization. Finally, based on the calibrated numerical dynamic models, performance of each well are predicted.

This systematic technique has been successfully applied K fractured-vuggy carbonate reservoir, which properly and correctly evaluate the properties of the reservoir. It also provides a reliable method for remaining oil evaluation and performance prediction, which are helpful for effective development of the reservoir. Furthermore, the systematic method can be used for reservoir evaluation and performance prediction in any other similar oil fields.