Dynamic Reservoir Characterization from Microbuildups with Formation Tester

Abstract

Historically, drillstem tests (DSTs) have been considered the standard for establishing the productive capacity of oil and gas reservoirs, providing measurements, such as formation pressure, permeability, and skin factor. In a recent study, the possibility of obtaining similar results was investigated by using wireline formation testing tool. The pressure-transient data obtained during the fluid-sampling cleanout operation was used to obtain reservoir properties. Of particular interest, spherical and radial flow models were successfully fit to very short buildup times (on the order of a few minutes) after pumpouts. To obtain similar formation properties from the shorter duration buildup times associated with flowline surging to clean debris (on the order of seconds), a process referred to as "sneezing" was investigated, yielding comparable results. Sneezing is performed several times during the fluid pumpout and sampling operation. Repetitive analyses of these microbuildups along with other pressure buildup periods in one pumpout location can help reduce uncertainty with respect to the estimation of formation properties. This paper presents three examples, including both oil- and gas-bearing formations, ranging in terms of lithology, permeability, and pressure. Formation permeability, skin damage, and reservoir-pressure values were evaluated from pressure-transient analyses during pumpouts. Results clearly demonstrate that zonal thickness, permeability, and anisotropy are key contributors to microbuildup analysis. Evaluation of reservoir properties is performed in real time with this approach to help optimize field-development plans. Analyzing these microbuildups is a unique method for supplementing/replacing the standard longer-duration pressure-transient analysis at the lowest-possible cost to the operator.