REVITALIZATION OF A MATURE VOLATILE AND CONDENSATE OIL RESERVOIR USING HORIZONTAL WELLS.

Abstract

The great interest shown in optimizing the exploitation of reservoirs, in the last two decades through the drilling of horizontal wells, has been the best evidence of the potential of this technology. Significant increments in production rates and recoveries have been reported even in oil fields considered uneconomic.

In this paper, the revitalization of the RG-14, COEF reservoir in the Santa Rosa Field by means of horizontal wells is analyzed. This reservoir is the most important mature reservoir producing volatile oil and condensate in Eastern Venezuela. The RG-14, COEF reservoir started its production in April of 1950, having been subjected to gas injection since 1955. Depth of the reservoir varies from 6560 ft subsea at the crest of the dome to 11150 ft at the flank. Presently, gas channeling and the subsequent entrampment of oil in undrained areas limit the recovery of 14.5 MMBls of remaining reserves. Consequently, the drilling of horizontal wells is a potential option to minimize gas channeling and maximize the drainage area, increasing crude production, final recovery and the economic feasibility of the project, at the same time.

This paper presents the integration of geological, reservoir and production studies to define undrained flow units, the selection of objective areas for three horizontal wells, the characterization of fluids, production forecast by means of pseudocompositional simulation and an economic analysis. A Peng-Robinson equation-of-state was used, to characterize both gas condensate and black oil. The simulation studies were performed only in the areas were horizontal wells are proposed, in order to compare them with vertical wells. Results indicate that it is feasible to reactivate production from the RG-14, COEF reservoir in the Santa Rosa Field from the current 567 STBD to a level of 2620 STBD through the drilling of three horizontal wells.

Introduction

In Corpoven's Anaco and San Tome traditional areas in the Eastern Venezuela Basin, there are about 134 mature fields of condensates and medium and light oil which still have reserves of between 50 and 300 million barrels. Secondary recovery processes (gas injection) used in these fields for the last 30 years have permitted the extraction of 75% of the initial estimated reserves. However, a good portion of the remaining reserves are still trapped due to inefficient drainage and preferential channeling of injected gas and/or water in the reservoirs subjected to a pressure maintenance.

Due to these circumstances, the use of the horizontal drilling technology is required in order to maximize the contact with undrained areas and so reduce the water and/or gas coning. Consequently, this procedure will permit the acceleration of the final recovery of reservoirs.

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