Revitalization of Mara Field

Abstract

Abstract The Mara field is located onshore on the western side of Lake Maracaibo in Western Venezuela and the PDVSA affiliate, Maraven, S.A., holds the concession rights for the field. The field was discovered in 1951 and has been producing since that time, but has always been considered a marginal prospect at best since its inception. The advent of new technology in seismic, wireline logs and in detection and identification of natural fractures in the reservoirs has now made it possible to revitalize the field's production potential and significantly extend its productive life. The reservoir rocks are of Cretaceous age, consist of carbonate lithofacies and are partially fractured. The new data and information from modern open hole wireline logs combined with the existing logs from the older wells, cores and production logs and borehole images were utilized to develop updated geological and petrophysical models. These models formed the basis for the Mara field rejuvenation and development plan. The new logs included Nuclear Magnetic Resonance (NMR), acoustic and borehole image logs. The borehole image logs were particularly useful in clearly identifying fracture zones as well as porous intervals that contribute to production. The NMR logs were useful in detecting the movable water zones for exclusion from the production intervals. Additional core analysis including determination of pore shapes and sizes were used in developing the petrophysical model. Fracture density and orientation were successfully correlated with regional tectonic events to update the geologic model. The production history and recent production logs confirm the validity of these new models. Introduction The Mara field of western Venezuela provides an excellent opportunity to assess the impact of modem logging technologies on field development strategies because a large variety of various vintages of logs were collected during the long history of field development. Since discovery of the field in 1951, a variety of logs have been utilized to describe the reservoir and to develop geological, petrophysical, and reservoir models. Only older E-logs were collected during the first phase of discovery and development although one density and two neutron logs were run in the last wells that were drilled (circa 1980). Suites of porosity, spectral gamma ray, resistivity, production, image, and Nuclear Magnetic Resonance logs have been run since reactivation of the field began in 1995. The modern log information proved critical for developing updated geological and petrophysical models in this complex and highly variable carbonate reservoir. These models have improved the success and production rates of new wells, and provide a rational for future development of the field.