The objective of the project is to develop a methodology for improving sweep efficiency and reducing CO2utilization rates by performing a detailed post-mortem on a mature carbon dioxide project that relates actual reservoir performance to predicted performance.
Louisiana State University, Baton Rouge, LA
Denbury Resources Inc., Plano, TX
CO2 displacement is a common improved recovery method applied to light oil reservoirs. The economic and technical success of CO2 floods is often limited by poor sweep efficiency or large CO2 utilization rates. Little Creek field in Mississippi is being studied to relate laboratory displacement results and simulated performance predictions to the historical reservoir performance to determine sweep efficiency, improve the understanding of the reservoir response to CO2 injection, and develop scaling methodologies to relate laboratory data and simulation results to predicted reservoir behavior.
This project is studying the effectiveness of CO2 flooding in a mature reservoir to identify and develop methods and strategies to improve oil recovery in CO2 floods. The study of Little Creek field will identify strategies to improve recovery from the reservoir through understanding conformance control and sweep in the current operations. Based on the knowledge gained during this study, methods will be developed for predicting conformance control and sweep efficiency that can be extended to other CO2 injection projects, in progress or planned, and ultimately yield improved oil recoveries due to CO2 flooding and reduce CO2 utilization rates.
The project was designed to be conducted in two primary tasks.
Task 1 is devoted to analyzing the historical performance of Little Creek field to evaluate the effectiveness of injection and production operations during the active CO2 flooding process. The research team is continuing the process of comparing performance predictions to actual historical performance data, including displacement studies, conformance issues, and sweep efficiency. Laboratory displacement studies have been designed and will provide a means to correlate actual reservoir performance to simulation studies and to other laboratory studies for CO2 flooding. Historical reservoir, production, and well data have been used to evaluate the effectiveness of CO2 injection and sweep in Little Creek field. Relatively simple univariate regression techniques appear to be as accurate as more complex techniques and are easier to apply and evaluate and also require fewer ad hoc assumptions than the more complex techniques. Several production logs have been run in active areas of the field to evaluate injection profiles in individual wells to identify vertical injection conformance or isolate injection issues. Simulation work utilizing the information from these logs has been completed for an active area of the field. Cased-hole logs to try to evaluate behind pipe saturations were designed, and test case areas were evaluated to allow the research team to quantify the measurements as best they could. A single well test on a well in the Soso Field was proposed and Denbury offered to test a second well with limited data which is more similar to the majority of wells in the fields they operate. These tests were performed and the results are currently being evaluated. If successful, these cased-hole logs may also be run in selected wells to estimate oil saturation throughout the Little Creek reservoir to verify sweep efficiency or identify potential unswept segments of the reservoir especially in the northeast quadrant of the field, which has been shut-in for nearly 10 years and may be economically productive at current oil prices. Successful results may also be cause for expansion of the logging program to other fields operated by Denbury Resources to attempt to better understand sweep in those fields. Historical reservoir performance both prior to and after initiation of the CO2 flood have been matched in simulation studies. These studies were undertaken in order to develop a system of dynamic reservoir models for use in predicting performance based on actual reservoir conditions. The emphasis has been on integrating the understanding developed in the various activities to improve CO2 sweep. The remainder of this portion of the project will be to extend that understanding to other reservoirs by developing application guidelines and recommendations for efficient CO2 sweep. Note that the project is also leveraging a large quantity of geological and engineering information provided to Denbury from Shell in order to evaluate potential differences between the original flood design and current operations.
Task 2 focuses on extending the findings of Task 1 to reservoirs that may be CO2 flooding candidates. This includes reservoirs with light oils comparable to Little Creek field and also reservoirs with heavy oils (10-20o API) where the potential for CO2 flooding needs additional study, especially relative to sweep effects due to the viscosity variation between the CO2 and viscous reservoir oils and due to the lack of complete miscibility between the oil and the CO2. Denbury has several target reservoirs in eastern Mississippi that will serve as candidate reservoirs for this task and has agreed to consider implementing ideas developed to improve oil recovery. Work has begun on evaluating CO2 displacement in heavy oil systems using the Martinville Field as a test case. Denbury has provided data related to this heavy (14o API) oil flood which has experienced poor sweep due to early CO2 breakthrough. A full fluid analysis has been provided and PVT modeling studies have begun as has a reservoir simulation study to understand the root causes for the poor performance. The task will then be to relate the results from this work to those in Task 1 in order to improve the confidence of recovery estimates made for this application, improve understanding of the feasibility of CO2 flooding heavy oil reservoirs and understand obstacles that need to be overcome, and potential solutions to those obstacles.
This project has been completed and the final report is available below under "Additional Information".
$315,316 (32 percent of total)
Final Project Report [PDF-2.00MB]
Tran, N. “Evaluation and Enhancement of Miscible Carbon Dioxide Flooding,” 2005 MS thesis, University of Oklahoma, Norman, OK.
Wiggins, M.L. and Hughes, R.G. “Evaluation and Enhancement of Carbon Dioxide Flooding Through Sweep Improvement—Annual Technical Report”, December 2005.