A major numerical modelling project was performed with the objectives of develop a more robust model for development planning studies. The second was to gain a better understanding of "reservoir dynamics", in particular aquifer influx, the lateral pressure distribution and gross fluid movement within the major reservoirs of the Wara–Burgan sequence and the flow between them.
The challenges and implemented solutions of history matching a reservoir model of a huge, complex field with multiple production zones, many wells and large volumes of production and surveillance data are described in the context of a recently completed study of Wara–Burgan reservoir in the giant Greater Burgan field. Additional challenges due to possible mechanical problems in wells and uncertainties in production and injection data, as usually experienced in mature fields, are also discussed.
The work started with reviews of basic engineering data, previous simulation studies and the regional geology. It was the first project for this field in which modern assisted history matching (AHM) techniques were applied. The main enablers for this were increased computational resources and the availability of new generation high-performance reservoir simulators. AHM techniques were used to help better define "high level" features of aquifer properties, pressure communication and gross fluid movement within and between the main reservoir units. A large emphasis was given to matching the pressure data from RFTs and cased-hole saturation estimates.
A combination of AHM and more traditional calibration methods have enabled improved models of the Wara-Burgan reservoir to be developed. These models account for the gross aspects of pressure and fluid movements in and between major reservoir units and provide a reasonable match of the performance at field, reservoir unit and gathering center (GC) levels. The use of AHM techniques and special plots to assess the quality of the pressure match have enabled better characterization on permeability levels and allowed lateral pressure gradients to be better represented. As the match was refined, issues with well histories become more apparent and the approach to dealing with these problems is discussed. Matching the apparent remaining oil distribution was facilitated by extensive tools that allowed easy comparison of simulation with both saturation estimates at wells from cased-hole logs and to interpreted saturation maps.
The available workflows, simulation tools and computing environment also allowed models with different levels of refinement (4 to 28 million cells) to be used to address concerns about numerical resolution and upscaling.
Base "Do-Nothing" prediction cases were also performed. These gave some insight into how sensitive prediction results would be to model calibration assumptions.
Development of the current representative numerical model for the main (Wara – Burgan) reservoir of the giant Greater Burgan field has allowed the major features of pressure communication, fluid movement and current pressure and fluid distributions all to be captured in a geologically plausible setting.
The approach to using very large volumes of data, including log data, in the AHM work and the novel tools used to assist visualization of match quality will be discussed.