Meren Field-The Geology and Reservoir Characteristics of a Nigerian Offshore Field

Abstract

Summary The Meren field is located offshore Nigeria. The field contains 1.3 billion bbl original oil in place (OOIP) and may be classed as a major oil accumulation. The more landward-lying fault blocks within the field contain an increasingly greater preponderance of oil reserves to gas reserves. All field pays display evidence of the depositional process occurring contemporaneously with fault movement. Sand sections have a tendency to become magnified in the downthrown portion of a fault block. The reservoirs are composed of sandstone with minor accumulations of authigenic kaolinite. The amount of kaolinite within a particular sand is a major factor in determining the porosity and permeability. The high porosities and permeabilities and the ability of the reservoir rock to remain unaltered by the introduction of seawater should minimize many of the operational problems ordinarily coincident with the installation of a water-injection project in the Meren field. This study indicates the possibility of using a combination of well-log interpretation with laboratory analyses of sidewall cores to help determine the areal variation of porosity and permeability within a particular reservoir. Introduction The Meren field is jointly owned by Nigerian Natl. Petroleum Co. (NNPC) (60%) and Gulf Oil Co. (40%); however, the field is operated be Gulf Oil Co. (Nigeria) Ltd. (GOCON). Fig. 1 shows the location of the field, offshore Bendel State and approximately 25 miles northwest of the GOCON/NNPC Escravos River Tank Farm and Export Terminal. The water depth in the field varies from 48 to 60 ft. Fifty-seven wells have been drilled in the Meren field, three of which are dry holes. The field was discovered in 1965. Production began in Sept. 1968. As of July 1, 1980. the Meren field has produced 347,194,961 STB oil, 321,545,190 Mcf gas, and 10,123,132 bbl water. Cumulative recovery is 26% OOIP. Performance analysis has shown that the majority of the reservoirs producing from the Meren field are being affected by minimal water influx. The reservoirs appear to be producing by a depletion-drive/gas-cap expansion mechanism. In 1978 GOCON and NNPC authorized a full-fledged feasibility study to determine the true worth of enhancing oil recovery from the Meren field. The first portion of the study ascertained reservoir configurations and their reservoir rock and fluid characteristics. The following segments were contained in this preliminary field definition study. Geological Study The Meren field was subjected to a complete geological study. All geological data were analyzed, and proper corrections were made to the original interpretations. Core Analysis The Meren 57 well was drilled and cored in late 1978 to confirm the results of the coring of the Meren 5 well in 1968. JPT P. 2095^