Understanding the heterogeneity is critical for a successful water injection in a carbonate reservoir. Thief zone is one of the most obvious forms of heterogeneity, which indicates the thin layer with higher permeability compared with average reservoir permeability. The existence of thief zone results in earlier water breakthrough and faster water cut increase, which lead to smaller sweep efficiency and lower recovery factor. Therefore, determining the thief zone distribution and proposing corresponding development plan are very important.
This paper focuses on a super-giant carbonate reservoir, which is a Cretaceous carbonate reservoir in Middle East, with an OOIP of more than 20 billion barrels. Thief zones are widely distributed in this carbonate according to the production logging test (PLT). In this paper, we combined geological understanding and dynamic behavior to summarize different types of thief zone distribution, which means the different locations and scales of thief zone and barriers. Then, geological model is built, and reservoir simulation is conducted on the models corresponding to different types to optimize the development strategy.
The optimized parameters include well pattern and perforation strategy. Then, development strategies are proposed for different types of thief zone distribution. Results indicate that location of thief zone hasobvious impact on the production. In order to mitigate the impact of thief zone, line drive pattern is preferred when the permeability ratio is high. Most importantly, different types of thief zone distribution require specified perforation strategy, and optimizeddevelopment strategies could save more than 25% of injected water by mitigating the futile cycle of injected water.
This paper offers a case study that summarizes different types of thief zone distribution and optimizes the development strategy for different scenarios. It also provides a methodology and reference case for engineers and geologists to develop other similar fields.