Screening Criteria for Application of Carbon Dioxide Miscible Displacement in Waterflooded Reservoirs Containing Light Oil
Authors: Diaz Daniel , Bassiouni Zaki , Kimbrell William , Wolcott Joanne 
Published: December 2007

Abstract
In conjunction with a joint Texaco/DOE research project, the LSU Department of Petroleum Engineering developed an improved method of screening reservoirs for the application of the carbon dioxide miscible enhanced oil recovery (EOR) process. This method, which can be applied to a large number of reservoirs, considers both the technical and economic feasibility of the EOR process.
The technical parameters of each reservoir are first compared to those of an "ideal" reservoir; and from that comparison, each reservoir is assigned a technical ranking. The technical ranking is used to estimate expected recovery. Key technical parameters used in the screening process are remaining oil in place, minimum miscibility pressure, reservoir depth, oil API gravity, and formation dip angle.
The reservoirs are subsequently screened for economic feasibility based on standardized capital costs and operation expenses that are representative of the reservoirs under consideration. The reservoirs are finally ranked based on the present worth value of revenues to costs ratio.
Using this method, we screened a database containing 197 light-oil reservoirs in Louisiana. The database includes three reservoirs where CO2 miscible floods are ongoing; these reservoirs ranked first, fifth, and thirtieth. The high ranking of these reservoirs, which were identified based on detailed and comprehensive reservoir studies, validates the screening method.
Different application options in a specific reservoir can be screened, if warranted, by using CO2 -PROPHET, a PC compatible software. CO2 -PROPHET is a relatively simple numerical model capable of simulating water and gas floods. An example of its application is included.

Introduction
In 1992, Texaco Exploration and Production Inc. (TEPI) and the U. S. Department of Energy (DOE) entered into a cost-sharing cooperative agreement to conduct an enhanced oil recovery demonstration at Port Neches field, Orange County, Texas. The agreement was formulated under the DOE Class I oil program, which encourages the development of innovative technical approaches to enhanced oil recovery. The innovative aspect of this project is the application of CO2 miscible flooding in waterflooded light-oil fluvial-dominated reservoirs. TEPI agreed to disseminate the knowledge and the experience gained at Port Neches to other operators in the petroleum field.
Louisiana State University (LSU) has agreed to assist TEPI with technology transfer efforts. LSU's role was mainly to identify and rank waterflooded Louisiana reservoirs where the CO2 EOR process may be used. To achieve this goal, LSU needed to develop a screening process that could be applied to reservoirs listed in the Louisiana Office of Conservation database. To be meaningful to interested operators, the screening method had to consider both the technical and economic feasibility of the EOR process. Because economic feasibility depends highly on CO2 availability, identifying CO2 sources and their distances to prospective reservoirs was imperative.
Once a prospect is identified, management options need to be considered. This task requires a user friendly numerical simulator. The effect of reservoir heterogeneity and well locations which is not considered in the initial screening can be investigated during the numerical simulations.

Screening for Technical Feasibility
Screening is usually performed following certain guidelines and criteria developed from laboratory tests and field experience. Screening methods include reservoir performance prediction, binary comparison, and parametric optimization. Reservoir performance prediction was excluded because of the relatively large number of reservoirs screened.
Binary comparison is easy to perform; it involves comparing a candidate reservoir's parameters against established ranges.
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