Development Strategy Optimization and Application for Fractured-Vuggy Carbonate Gas Condensate Reservoirs

Abstract 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, high production decline rate and low estimated ultimate recovery. So how to properly develop this kind of reservoirs is a major challenge. This paper presents the study on development strategy optimization for fractured-vuggy carbonate gas condensate reservoirs in detail. Based on the geological survey of palaeokarst outcrops and seismic interpretation, representative reservoir type patterns of fractured-vuggy carbonate gas condensate reservoirs can be determined. And combined geological study and dynamic characterization, different reservoir patterns can be identified and characterized. After that, simulation models of different reservoir patterns are built, in order to study the detailed development strategy on primary depletion and water flooding huff-and-puff. And optimal development strategies are applied into the TZ fractured-vuggy carbonate gas condensate reservoir in China. Take TZ carbonate gas condensate reservoir in China for example. The mid-depth of TZ reservoir is 5500m with annual production decline rate higher than 25%. Through geological and dynamic characterization, six representative reservoir type patterns are identified and characterized. And more than half drilled patterns in TZ are isolated and developed in very limited volume, which only need one well to develop each pattern. Then reservoir simulation models of the six patterns are built to investigate the optimized development strategies. The results show vertical wells are optimum for four patterns and horizontal wells are optimum for two patterns. For isolated karst caves pattern, there are still lots of remaining condensate oil after primary depletion, so water injection huff-and-puff are studied for this pattern. The results are applied to TZ reservoir. This paper offers a case study on development strategy optimization of different reservoir patterns for fractured-caved gas condensate carbonate reservoirs, and the understandings are successfully applied to TZ carbonate gas condensate reservoir. It also provides a methodology and an improved oil recovery reference case for engineers and geologists to develop other similar reservoirs.