Light-Oil Steamflooding An Emerging Technology

Abstract

Summary This paper discusses the extension of the steamflood process to the recovery of light oil and the state of the art of this emerging technology. A review of the various steamflood mechanisms indicates that distillation will dominate if steam is injected into light-oil reservoirs. The results of light-oil steamflood laboratory studies, computer simulations, and field projects are also reviewed. A rough screening guide for selecting a light- projects are also reviewed. A rough screening guide for selecting a light- oil steamflood candidate is discussed. New areas of advanced steamflooding technology need to be developed and field tested before light-oil steamflooding can be applied on a routine basis, as is currently the case for heavy-oil steamflooding. Introduction Steam injection is the principal EOR method used today, accounting for 75% of oil produced in the U.S. by enhanced recovery methods. Table 1 delineates the U.S. thermal EOR production from 1976 to 1980. Steamdrive- and steamsoak- (huff ‘n' puff) assisted production has steadily increased from 235,000 B/D [37,362 m3/d] in 1976 to 296,000 B/D [47,060 m3/d] in 1980. The most notable development in the growth of steam-assisted recovery is the increase of steamdrive EOR production. Oil recovered by steamflooding technology has increased from 105,000 to 155,500 B/D [16,694 to 24,723 m3/d] in 5 years, a 48% growth rate in the period 1976–80. Steamsoak production remained fairly constant during this same time period. Table 2 summarizes the number of active thermal EOR projects-- combustion, steamsoak, and steamdrive--during the last 10 years. While there may be some question as to what constitutes a "project," it is clear that the number of steam projects has grown steadily while the number of combustion projects has declined. Again, the number of steamdrive projects has increased dramatically during the last 5 years, from 31 projects in 1976 to 61 projects in 1980. This shift to steamdrive is probably attributable to two factors. One is the relatively high ultimate oil recovery of steamdrive compared with that obtainable by cyclic steam. The other is higher oil prices that have made steamdrive projects economically attractive at the relatively higher steam/oil ratios that are characteristic of steamfloods. What types of reservoirs and reservoir oils are candidates for steamdrives? Farouq Ali and Meldau presented a list of successful steamfloods. Of the 15 successful steamflood projects listed, 7 projects had in-situ reservoir oil viscosities of 1,000 cp [1 Pa s] or projects had in-situ reservoir oil viscosities of 1,000 cp [1 Pa s] or higher. All projects except one were completed at a depth of 2,600 ft [792 m] or less. Reservoir pressures were 300 psi [2.1 MPa] or less for all the projects. These properties are typical of heavy-oil reservoirs that are projects. These properties are typical of heavy-oil reservoirs that are prime candidates for thermal methods because of the effectiveness of heat prime candidates for thermal methods because of the effectiveness of heat in lowering oil viscosity. Included in the steamflood projects reported by Farouq Ali and Meldau are three projects (Brea, Coalinga, Smackover) that are or were conducted in reservoirs containing oils with viscosities of 100 cp [0.1 Pa s] or less. These projects were reported to have steam/oil ratios of 2.8 to 4.0. The Brea field (CA) steamdrive was referred to as a test to determine the feasibility of driving a relatively light (24 API [0.91-g/cm3]), low-viscosity (6-cp [0.006-Pa s]), volatile oil with steam. The definition of light and heavy oil based on crude-oil properties is somewhat arbitrary. The U.S. DOE defines heavy oil as having an API gravity of less than 20 [0.93 g/cm3]. At a recent UNITAR meeting in Caracas, the conference proposed a definition of heavy oil as: "Heavy oil has a gas-free viscosity of 100 to 10,000 centipoise inclusive at original reservoir temperature or a density of 20API to 10API inclusive at 60F at atmospheric pressure."Crude oil (other than tar sand oil) not described by this definition would be classified as medium or light crude oil. A review of the steamdrive projects summarized in an EOR survey indicates that two to four steamdrive projects during the last 10 years could be classified as light-oil or medium-oil steamfloods according to the UNITAR heavy-oil definition. These projects are listed separately from the heavy-oil steamflood projects in Table 2. In 1982, the light-oil steamfloods in progress or announced by the oil industry totaled nine projects. Can steamflood technology be extended economically to light-oil projects. Can steamflood technology be extended economically to light-oil reservoirs? What are the dominant recovery mechanisms during a light-oil steamflood? What are some of the reservoir characteristics for the limited number of successful light-oil steamfloods completed? What are some of the economic and technological barriers that need to be overcome before light-oil steamflooding is applied as routinely as heavy-oil steamflooding is today? This paper discusses the extension of the steamflood process to oil recovery from medium- and light-oil reservoirs and addresses some of these questions. JPT p. 1115