Multi-Method of Estimating Lifecycle Technical Ultimate Recovery in a Natural Depletion Gas Reservoir

Abstract

Gas reservoir development at inception is often linked to detailed surface infrastructure development and long term contractual agreements with only a few appraisal wells. A thorough and detailed technical estimation of the size of the pie is an important step in the right direction. This is characterized by seismic acquisition and interpretation, scanty appraisal wells proving useful reservoir and fluids properties data and contact tagging. Calibration of regional properties with nearfield analogue can also be quite useful. All these form the basis of the field/Reservoir development plan. For a gas development, the optimum development wells depend on a variety of factors identified at the field development stage often targeting the most viable crestal part of the reservoir for optimal development. Post drilling of development wells where reservoir static properties are fairly known and at the early stage of production when there is paucity of production data, it is imperative to adopt a robust approach to evaluate the technical UR. In early producing life of the reservoir when reservoir pressure data is needed perhaps the most, long shuttin-in to take static pressures can be abit problematic due to commercial commitments. There is heavy reliance on planned and unplanned shutins to take useful pressure data used in calibrating reservoir models. This paper takes a critical look at multiple approaches to estimating robust ultimate recoverable gas volumes with reservoir geology as an essential guide using tow distinc approaches; Detailed 3D simulation model and P/Z estimate method using Piper, McCain and Corredor z factor estimates. Lastly the range of uncertainties of the input data was used to estimate the low base and high cases.