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Abstract
CO2 flooding in oil reservoirs to enhance oil recovery is successfully applied
in many ongoing projects in the world. The bulk of industry research and field
testing of CO2 has been directed towards miscible displacement. This method of
using CO2 appears to have the greatest potential for recovery of oil that would
not have been recovered using conventional production methods.
The main objectives of this paper are to investigate the most important
reservoir and operational parameters in CO2 flooding and to provide guidelines
to maximize CO2 injection performance for different levels of reservoir
heterogeneity. Several compositional simulation models were generated using
actual field data. For each model, reservoir heterogeneity was evaluated using
Lorenz and Dykstra Parsons coefficients. The different compositional simulation
models were setup to investigate the effects of key parameters such as
injection rates, injection patterns, well spacing, injection scheme (Continuous
CO2, WAG, and SWAG), WAG cycle length, vertical to horizontal permeability, and
horizontal injection wells on the recovery factor and production of CO2
projects.
Those different heterogeneous models were used to simulate different scenarios
over a wide range of both reservoir and operational parameters and provided a
comprehensive data set to evaluate the CO2 flood effectiveness in a variety of
conditions. More than 700 simulation runs were designed using Experimental
Design techniques to test those parameters. Several correlations (proxy models)
were also developed and blind tested to check their effectiveness in predicting
the performance of combination of parameters that were not even tested. As a
result of this work, it is possible to use experimental design to test the
performance of CO2 injection. It can be performed with acceptable accuracy by
performing a limited number of runs; hence, reducing the time, effort, and
money.
It was observed that the use of different heterogeneous models resulted in
different overall field performance. Our results also showed that implementing
WAG and horizontal wells enhance the oil recovery significantly.
Introduction
Carbon Dioxide gas injection has been becoming increasingly important for oil
recovery and environmental considerations in oil field development and CO2
sequestration. The miscible CO2 gas injection is becoming more and more popular
amongst other EOR techniques. This can be related to the higher oil prices as
well as the availability of more CO2 sources considering the global regulations
and restrictions on CO2 emissions.
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