ABSTRACT

Stratigraphic compartmentalization results in effective segregation of flow units and incomplete recovery due to depositional and diagenetic heterogeneities within nonassociated natural gas reservoirs. Three examples of reservoirs that contain secondary gas resources in Stratton field are used to illustrate the type of incremental resources that may be common in fluvial reservoirs in mature gas fields. The incremental resource within each of the reservoirs studied ranges from approximately 1 to 2.6 Bcf per example. Depositional facies and lithologic boundaries identified as potential barriers to gas flow include the transition from floodplain mudstone and siltstones to channel-fill and splay sandstones, channel-to-channel contacts, and interchannel facies variability.

Resource additions are demonstrated by examples of (1) new infield reservoirs comprising fluvial channel sandstones between the previous well spacing, (2) untapped reservoir compartments that maintain pressure integrity from effective vertical and lateral interreservoir lithologic barriers to gas flow, and (3) incompletely drained reservoir compartments where initial completion pressures as low as one-third of original reservoir pressure still provide a significant incremental gas resource. Determination of the static reservoir pressure and drawdown testing in targeted completions establish the size of the reservoir and the volume for typical fluvial-deltaic gas reservoirs, which account for a significant portion of nonassociated gas reservoirs in the Gulf Coast Basin.