Reservoir Characterization of a Fractured Reservoir Using Automatic History Matching

Abstract

Abstract The Subject oil reservoir will not be identified to preserve requests of confidentiality. Oil production from the Subject field is primarily from a highly fractured and faulted formation. The initial reservoir pressure is several thousand psi above the bubble point pressure. Pressure surveys after one year of production mdicated a recharge source. The source of the pressure support could be from (a) the matrix volume assuming a dual porosity system, (b) an aqwfer composite system or (c) an oil filled composite system with a low permeability outer zone. Matching the pressure data with any of these reservoir descriptions would establish the most plausible reservoir characterization. However, to carry out the task of varying the parameters of each reservoir description until a satisfactory match is obtained for that particular description would be extremely onerous and time consuming if done manually. To solve this problem, a three-dimensional three-phase reservoir simulator with automatic history matching capability was used. The simulator was able to obtain the best possible match for each reservoir description by regressmg on the porosity and directional permeability parameters. The competing models were then compared and the model that matched the historical pressure observations as well as conforming to the established parameters of the geological model was determined to be the true model. The results of the above analysis indicated that the dual porosity system did not provide an acceptable fit of the pressure data and thus it was rejected. Excellent matches were obtained with the aquifer composite model and the oil filled composite model. The parameters of the aquifer composite model that were necessary to obtain a match did not conform with other geological and pressure transient analysis mformatlon. However the oil filled composite model parameters were in close agreement with the well test interpretation model and the geological features of the reservoir. This was the model that was fmally accepted. Thus automatic history matching was a valuable tool in the reservoir characterization of the Subject Reservoir.