Case Study of a Low-Permeability Volatile Oil Field Using Individual-Well Advanced Decline Curve Analysis

Abstract

ABSTRACT This paper presents a detailed case history study of a low permeability volatile oil field located in Campbell County, Wyoming. The field was analyzed on an individual well basis using advanced decline curve analysis for 40 individual well completions. Well permeabilities, skins and original oil in place are calculated for each well from rate-time analysis using constant wellbore pressure type curve analysis techniques. Original oil in place values calculated from rate-time analysis for individual wells are used with recoverable reserve projections from the decline analysis to obtain fractional recoveries for each well. Gas-oil ratios versus fractional recovery curves are also made for each well using historical cumulative production and the calculated oil in place values. Ultimate fractional recovery numbers and GOR vs fractional recovery curves, plotted for each well, are shown to suggest different rock types and reservoir fluids. Multi-well decline curve analysis shows the validity of the variables s (skin), k, 00IP, ultimate fractional recovery and G0R vs fractional recovery evaluated from each well's type curve evaluation. These variables must all give consistent and reasonable numbers when compared with each other. A single well analysis can easily give results that are not recognized as being invalid unless compared with other wells in the field. The study also illustrates flowing and pumping well backpressure changes in a well's decline, the method of handling such changes, and their effect on ultimate recoverable reserves predictions. Conventional decline curve analysis can not handle backpressure changes because of its constraint that what controls the decline in the past will also continue in the future.