Thermal Recovery In The Venezuelan Heavy Oil Belt

Abstract

This paper describes a successful cyclic stea1n injection program in the Jobo Field, located on the northeastern edge of the Venezuelan Heavy Oil Belt. The program was commenced in 1974 by Amoco International Oil Company. It is being continued, following reversion, by Amoven, S.A., a subsidiary of Petroleos de Venezuela. The Jobo reservoirs are highly unconsolidated sandstones at a depth of approximately 3,800 feet. The crude gravities range from 9 to 13.5 °API. Wells were completed on 64-acre spacing utilizing techniques designed to withstand thermal processes. A portable steam generator rated at 30 MMBtu per hour is used and the steamed wells have received between 4,000 and 8,000 metric tons each. This corresponds to between 150 and 200 MMBtu per foot of pay. The wells are placed on production after soak periods varying from one week to one month. In the eleven wells which have been steamed at this writing, peak oil producing rates ranging from two to five times the pre-steam rates have been realized almost immediately on commencement of production. The techniques described herein have permitted injection of high-quality steam at appreciable depths while avoiding m.ost of the common problems normally expected, such as bottom-hole equipment failures, casing cement and liner failures, and surface equipment malfunctions. Introduction STEAM STIMULATION is a well-established technique developed in the early sixties. It has found extensive application in Venezuela, mostly in shallow heavy oil reservoirs ranging in depth from 300 to 3,000 feet and containing oil of moderate gravity ranging from 14 ° to 20 °API. Success has been notable in several areas, mostly along the Juseping trend in eastern Venezuela and the Bolivar Coast on the eastern shore of Lake Maracaibo. The technique has not been very successful where the reservoir and crude oil properties vary appreciably from the ranges given above. This is the case in the northern portion of the Orinoco Heavy Oil Belt; the reservoir depth is between 3,600 and 4,000 feet, the oil viscosity averages 1,800 SFS and the oil gravity ranges between 8.5 and 13 °API. This paper describes a successful steam stimulation project in the Jobo Field, located on the extreme northeastern edge of the Orinoco Heavy Oil Belt. The project is notable as a demonstration of the successful application of steam stimulation under conditions of extreme depth, viscosity and gravity. Field Description Figure 1 is a map of Venezuela, showing the location of the Jobo Field with respect to the vast Orinoco Heavy Oil Belt. The heavy oil belt contains some 700 billion barrels of oil in place, but has seen only scattered development on the extreme northern fringe. Jobo underlies a 5,500-acre concession originally granted to Amoco Venezuela Oil Company and now under the administration of Amoven, S.A., a wholly owned subsidiary of Petroleos de Venezuela, S.A. The productive Oficina Sandstone at Jobo is separated into two distinct reservoirs, designated Group I and II.