Field Histories Show Benefits of Gas and Water-Injection Projects in Eastern Venezuela

Abstract

Introduction Pressure maintenance depletion of appropriate reservoirs by fluid injection has been practiced in Eastern Venezuela since 1948. This program has resulted in benefits such as increased ultimate recovery, lowered artificial-lift costs and, in the case of gas injection, lowered treating costs and the conservation of natural gas which otherwise would be flared. The L1 sand, OG–56 reservoir, has been under a gas-injection pressure maintenance program since 1948. The oil recovery from this reservoir as of Aug. 31, 1959 had been increased 4.75 per cent over that predicted by natural depletion. This is approximately 6.3 million bbl of additional recovery, with all present outlets still on natural-flow production. The ultimate recovery by this means of depletion is 42 per cent of the original stock-tank oil in place, or 55.9 million STB. The G sand, 00–271 reservoir, was subjected to a pressure maintenance, water-injection program in May, 1954. As of Aug. 30, 1959, 34.5 per cent of original reserves (or 9.29 million STB of oil) had been produced. This represents an increase of 5.8 per cent, or 1.56 million bbl, over the predicted pressure-depletion recovery. Gas Injection in L1 Sand, OG–56 Reservoir, Central Oficina Field Reservoir Characteristics The L1 sand, OG–56 reservoir, is a north-south trending, fork-shaped channel deposit. The south boundary is defined by the Caris fault, the flanks by sand thinning and the downdip boundary by the water-oil contact at approximately 4,480 ft subsea. The reservoir consists of two segments separated by a shale break which varies from 1 ft to several feet in thickness. The segments are in pressure communication and are considered a single reservoir. Four of the 82 wells drilled in this sand cored the L1. Some 22 ft of L1 core was recovered and analyzed. The sand ranges from a coarse-grained, well sorted, clean sandstone with high permeabilities and porosities to medium-grained, poorly sorted, silty sandstone with clayey laminations at the top and bottom of the sand. (See Table 1.) The permeability ranges from 300 md in the dirtier sand to 8 darcies in the center portion of the cores. The weighted porosity was found to be 24 per cent.