Control of Waste Gas From a Thermal EOR Operation
Authors: Peavy M.A , Braun J.E. 
Published: December 2007

Summary
This paper summarizes a waste-gas treatment system designed to control emissions from thermal EOR wells. This case study discusses the need, design, installation, and operation of the system.

Introduction
Thermal EOR operations that use cyclic and continuous steam injection into the reservoir generate return vapors. Controlling these vapors offers environmental and operational benefits. This paper discusses the construction and operation of a wellbore-vapor-recovery system. Oryx Energy Co. operated about 934 wells in the Midway-Sunset field under casing-vapor-recovery systems (CVRS's). Emissions collected from well-casing vent gas contain hydrocarbons and hydrogen sulfide. Emissions are collected and processed through CVRS skids composed of processed through CVRS skids composed of condensers, compressors, and pumps that separate fluids from the waste-gas stream. Noncondensible gas is then incinerated to reduce hydrocarbon and sulfur emissions into the atmosphere. About 160,743 Ibm/D of hydrocarbon and 3,558 lbm/D of sulfur dioxide (SO2) are removed from the atmosphere from wells contained within these Oryx-operated systems. These hydrocarbons yield about 550 BOPD. The system helps manage the pressure differential from the reservoir into each wellbore and helps improve ambient air quality in Kern County, CA.

Field History
The Midway Sunset field is in the southwest corner of the San Joaquin Valley in Kern County (Fig. 1). The field extends southeast from the town of McKittrick along the Temblor Range foothills for more than 25 miles to the town of Maricopa. The field has an average width of 3 1/2 miles and encompasses more than 50,000 acres. It is the second largest oil-producing field in California and is one of the largest fields in terms of reserves within the continental U.S. About 155,000 BOPD is produced from 9,200 wells in the field. The arid topography varies from gently sloping alluvial fans to smoothly rounded hills, occasionally split by gullies. Surface elevations range from 500 to more than 1,700 ft above sea level, with the productive interval occurring from just below the productive interval occurring from just below the surface to depths below 2,000 ft. The Potter formation, a heavy-oil reservoir with oil Potter formation, a heavy-oil reservoir with oil gravities ranging from 9 to 12deg. API, is the field's primary producing zone. The first recorded oil well was drilled before 1890. The first spectacular gusher, recorded in 1909, was located near Fellows, CA, and flowed in excess of 3,000 BOPD. By 1916, more than 100 gushers flowing more than 1,000 BOPD had been placed on production. Since then, reservoir pressures production. Since then, reservoir pressures have declined, and now artificial lift is required to assist fluids to the surface. Development of the field increased drastically around 1960, with greater demand for low-gravity crude and the development and refinement of thermal recovery techniques, such as firefloods, cyclic steaming, and more recently, continuous steam injection. Thermal recovery is a process in which heat is intentionally introduced into a subsurface accumulation of organic compounds to recover fuels through wells. The primary thermal enhancement technique initiated within the Midway Sunset field in the 1960's was injection of steam into wellbores. Generally, 1 bbl of crude oil or its equivalent is fired in a steam generator and the steam is injected into the reservoir to produce about 10 bbl of crude. Heat derived produce about 10 bbl of crude. Heat derived from the steam is used to improve the displacement and recovery efficiency of the reservoir. The major benefit of heat is that the higher temperature reduces crude oil viscosity, allowing the oil to flow more freely into wellbores. Oryx operated about 934 thermal EOR wells located on seven leases (Fig. 2). Oryx divested these properties in late 1990.