Carbon Dioxide Displacement of a West Texas Reservoir Oil

Abstract

Yellig, William F., SPE, Amoco Production Co. Abstract This paper presents results of an extensive study to understand CO2 displacement of Levelland (TX) reservoir oil. The work was conducted to support Levelland CO2 pilots currently in progress. Experimental displacement tests were conducted at various pressures, core lengths, and CO2 frontal advance rates. The experimental system included a novel analytical technique to obtain effluent compositional profiles within the oil-moving zone at test conditions. The results of this study show that at pressures greater than the CO2 minimum miscibility pressure (MMP), a multicontact miscible displacement mechanism predominates. Miscibility is developed in situ by vaporization or extraction-type mass transfer. The laboratory lengths required for CO2 to develop miscibility and exhibit miscible displacement efficiency were found dependent on the phase equilibria of the CO2/Levelland oil system. Displacements requiring the greatest length to develop miscibility were at pressures where single-contact mixtures of CO2 and Levelland oil form two liquid phases. A companion paper demonstrates the use of the analytical technique developed in this study to obtain process data from a CO2 field pilot test. In addition, the mechanistic information obtained from this study is used to interpret the process data from the pilot test. The results have application to other reservoir oils whose phase equilibria with CO2 are similar to the CO2/ Levelland oil system. Introduction Miscible CO2 flooding is developing rapidly as a commercial enhanced oil-recovery process. The successful design and interpretation of CO2 pilot tests and fieldwide floods are dependent on a good knowledge of the reservoir and the CO2 displacement process. The overall CO2 displacement process is shown schematically in Fig. 1. The main focus of this study concerned the oil moving zone (OMZ) and particularly the mechanisms by which this zone formed and by which CO2 displaced Levelland oil. Levelland oil was chosen because it is typical of many west Texas reservoir oils being considered for CO2 flooding. In addition, the CO2 pilot tests currently conducted in the Levelland field provide a direct application of this research. Several authors have discussed the displacement of reservoir oil by CO2. These discussions have centered around three primary displacement mechanisms: immiscible, multicontact or developed miscible, and contact miscible. In addition, two basic types of mass transfer have been postulated as responsible for the development of miscibility in a multicontact process: transfer of hydrocarbons from the in-place oil to the displacing CO2 (i.e., vaporization or extraction) and transfer of CO2 to the in-place oil (i.e., condensation). Vaporization and extraction are the same basic mass-transfer process. Vaporization refers to mass transfer from a liquid oil phase to a CO2-rich vapor phase and extraction refers to mass transfer from a liquid oil phase to a CO2-rich liquid phase. The distinction between vaporization and extraction is somewhat arbitrary in describing the CO2 process since it reflects the types of phases present only on first contact. One purpose of this paper is to present results of a comprehensive study to determine the mechanism by which CO2 displaces Levelland oil at reservoir conditions. SPEJ P. 805^

Effects of Mobile Water on Multiple-Contact Miscible Gas Displacements

“…15 It has also been shown that mobile water dramatically increases the OMZ length for first-contact miscible displacements. 5 • 7 • 12 It is not known whether longerlength systems would be required to generate miscibility in a multiple-contact process with mobile water present as has been shown in the absence of mobile water.…”

“…Several recent studies have shown that the CO 2 -displacement process is' controlled by a multiple-contact miscible process in which miscibility is developed by interphase mass transfer between the CO 2 and the in-place oil. [15][16][17][18][19] The purpose of this paper is to present the results of an extensive study of the effects of mobile water on the multiple-contact miscible gas displacement process, The focus of this experimental study was to determine effects on displacement efficiency and mass transfer of the multiple-contact miscible CO 2 displacement of recombined reservoir oil when water was injected simultaneously with the CO 2 , Emphases were placed on obtaining core-test produced-fluid compositions and on obtaining a suitable technique for making a normally water-wet core act as an oil-wet porous medium.…”

An Investigation of Phase-Behavior/Macroscopic-Bypassing Interaction in CO2 Flooding

“…2 are low because of an absolute length effect, as discussed by Yellig. 15 One-dimensional simulations predicting almost identical recovery efficiencies with 5 and 40 gridblocks provide weak evidence that such an effect should not be a significant factor in the displacement of Wasson crude by CO 2 at 2,000 psi [13 790 kPa]. However, the existence of an absolute length effect would indeed confound the picture in Fig.…”

Investigation of Miscibility Behavior of CO2 rich Hydrocarbon Systems – With Application for Gas Injection EOR

“…Several observations of Vapor-Liquid-Liquid Equilibrium (VLLE) phase behavior in oil-CO 2 systems have been reported in literature (Huang et al (1974), Shelton et al (1977), Metcalfe et al (1979), Yellig (1981), Orr et al (1981), Turek et al (1984), Larson et al (1989), and Stalkup (1992)). A further complexity may arise when the addition of CO 2 leads to precipitation of asphaltenes from the oil, which is either reported as a VLLE or more commonly as a Vapor-Liquid-Solid Equilibrium (VLSE) system.…”