Practical Application of Experimental Design ED to Improve Deterministic History Matching and Manage Uncertainty in Mature Waterflood Field Development
Authors: Sulaksana Alex , Thiam Flora , Tan Leong-Hooi , Garimela V. S. Sai 
Published: November 2016

Abstract
The paper intends to share the ideas and methodology on how to improve history matching and manage uncertainties by integrating the deterministic method and stochastic Experimental Design (ED) approach in the most practical way. The integrated method was applied in the re-development study of an offshore clastic oil Field. In the conventional deterministic approach, history matching is conducted by manually tuning the key parameters to achieve pressure and saturation matching iteratively. The main advantage of the deterministic approach is in providing the opportunity to understand the details of the well and reservoir local behaviors during the history matching exercise. The disadvantages are the workflow yields only a single outcome hence poses difficulty in quantifying the effect of multiple uncertainties and is dependent on the of engineer's subjective. Meanwhile, history matching stochastic workflow assisted by ED is a more systematic procedure built to capture the effect of uncertainties on the range of outcomes. However, the parameters used in the stochastic process is typically of global scale, thus the engineer may lose insight into the localized reservoir behaviors. Furthermore, proxies built in ED, although statistically consistent; do not always conform to the reservoir physics as most of the reservoir mechanisms are too complex for reliable modeling by ED-based proxy equations.
Candidate Field re-development study aimed to further improve recovery by infill drilling. Analysis of well production data suggested that the remaining oil was entrapped to the crestal region of the field. Full field simulation work was then conducted to target and quantify the infill opportunity. The integrated approach began with a structured deterministic history matching adopting the well-known stratigraphic method. The deterministic history matching involves mostly local modifications of the aquifer strength, fault sealing and well's PI multiplier to achieve satisfactory match on the well and reservoir level. This was then used as the starting base case for the ED workflow. ED History Match led to multiple best matched cases, which were then run in forecasting mode and yielded a range of outcomes. ED History Matching also proved to improve the match quality of the initial deterministic history matched model. Sweet-spotting exercise was performed based on multiple History Matched models and suggested 3 infill potential locations in the major reservoirs, providing three concepts of infill drilling: unpenetrated fault blocks, crestal oil accumulation and sub-optimum drainage area. After considering the risk and confidence level of each potential location, the crestal oil accumulation was selected as the most attractive. Having multiple best match models helped to provide the range of incremental UR that is consistent with the range of uncertainties.
The study demonstrated that integration of deterministic and stochastic history matching method has been instrumental in managing uncertainties and identifying redevelopment opportunities of a mature waterflood field.