Recovery of Cellar Oil By Water Injection

Abstract

Summary The effect of operating and reservoir parameters on cellar flooding were evaluated by use of a commercially available reservoir simulator. The parameters were representative of Miocene reservoirs and operating conditions in south Louisiana. Cellar flooding is a one-well injection/production process that exploits the density difference between injected water and in-place crude to recover oil from the "cellar" of a steeply dipping pressure-depleted reservoir by a gravity-segregation mechanism. The cellar of a reservoir is the volume located downdip of the most downdip well that produced from the segment. The results of computer simulation show that the most significant operating parameters are injection volume and migration time. The most significant reservoir parameter is well location. Criteria to select cellar flood candidates and guidelines to operate a cellar flood are presented. Introduction Reservoirs associated with shallow or piercement salt domes and other highly faulted areas are often small, with steeply dipping beds. The reservoir size is often such that only one well can be justified economically to recover primary oil. Some of these reservoirs produce by depletion drive, while others produce by a full or partial water drive. The drive mechanism may be supplemented, under certain conditions, by gravity drainage as discussed by Dykstra1 and Hagoort.2 Isolated reservoirs of the type under evaluation are produced by a combination depletion drive/gravity segregation mechanism. A high residual oil saturation remains down structure of the producing well as a result of gravity effects at the end of primary production. The drilling of additional wells or sidetracking of existing wells is usually not economical. The location of existing wells eliminates conventional waterflooding or other conventional methods to displace the down structure oil. Cellar flooding is a possible method to recover the down structure reserves. Cellar flooding is a single-well injection/production process that exploits the density difference between the injected water and in-place crude to recover oil from the "cellar" of a steeply dipping pressure depleted reservoir by a gravity segregation mechanism (Fig. 1). The "cellar" of a reservoir is the volume located downdip of the most downdip well that produced from the reservoir. Implementation of cellar flooding could increase oil recovery from developed fields and extend the utility of existing injection facilities as mature waterfloods reach an economic limit. Implementation of cellar flooding also could produce a profit from what otherwise could be operating expense associated with the eventual mandatory subsurface disposal of all produced brine. (In some areas produced brine is discharged to surface water bodies after treatment to remove oil.) Intermittent and continuous cellar flood processes were evaluated by Gaskell and Lindley3 in 1961 by use of a physical reservoir model. Intermittent cellar flooding is a cyclic process with three distinct phases: an injection phase, a shut-in/segregation phase, and a production phase. Continuous cellar flooding differs from an intermittent process in that there is no shut-in period. Production is maintained from the reservoir during water injection by completing the project well with a dual setting. A thicker pay zone and higher reservoir pressure are required to use continuous cellar flooding than to use intermittent cellar flooding. Gaskell and Lindley's model showed that either process could recover cellar oil. In addition to the model studies mentioned, work by Texaco U.S.A.4,5 and Humble Oil and Refining Co.6,7 has resulted in various patents on the cellar flood process.