Simulating Oil Recovery During CO2 Sequestration Into a Mature Oil Reservoir
Authors: Babak O. , Deutsch C.V. 
Published: March 2010

Utilization of CO2 for enhanced oil recovery (EOR) and sequestration processes not only reduces greenhouse emissions, but also awards economic benefits. Enhancing oil recovery using sequestration is an optimization process that requires careful analysis. In CO2 EOR, the main purpose is to maximize oil recovery using the minimum quantity of CO2, while at the same time, sequestering the maximum amount of CO2 in the field. The Kartaltepe Field, having 32 ºAPI gravity oil in a carbonate formation, in southeast Turkey has been considered in this study. Reservoir rock and fluid data were evaluated and merged into CMG's STARS simulator. A history matching study was done with production data to verify the results of the simulator with field data. From the results of the simulation runs, it was realized that CO2 injection can be applied to increase oil recovery, but sequestering high amounts of CO2 was found out to be inappropriate for the Kartaltepe Field. Therefore, it was decided to focus on oil recovery while CO2 was sequestered within the reservoir. Oil recovery was about 23% of OOIP for the field in 2006. It reached 43% of OOIP by injecting CO2 after properly defining production and injection scenarios.

Introduction

Global warming is a term used to describe the observed increases in the average temperature of the Earth's atmosphere and oceans. The average global temperature rose 0.6 ± 0.2 ºC over 150 years, and the scientific opinion on climate change is that it is likely that " most of the warming observed over the 20th century is attributable to human activities."(1,2)

Factors that may be contributing to global warming are the burning of coal and petroleum products (sources of anthropogenic greenhouse gases (GHG) such as carbon dioxide, methane, nitrous oxide, ozone) and deforestation(3). It is estimated that the global radiative forcing of anthropogenic carbon dioxide (CO2) is approximately 60% of the total due to all anthropogenic greenhouse gases so that climate change is mainly driven by emissions of CO2(4).

The United Nations Framework Convention on Climate Change (UNFCCC) was drafted in 1992 by a majority of the world's nations in response to global concern over human-induced climate change. A central, and often controversial, issue in these negotiations has been the use of terrestrial carbon sinks (e.g. forests, agricultural soils) to reduce CO2 emission levels(5). The Kyoto Protocol to the UNFCCC included provisions for industrialized nations to manage carbon sinks in order to meet specified emissions-reduction targets. Under the Kyoto Protocol to the UNFCCC, adopted in December 1997, industrialized nations agreed on a target to reduce their greenhouse gas emissions on an average of 6 to 8% below 1990 levels between the years 2008 and 2012(6).

Deep ocean and geologic sequestration are the only choices to dispose of large amounts of CO2 safely and economically for long-term periods. Geologic sequestration, a prospective technology to reduce large amounts of CO2 released into the atmosphere, involves the capture of CO2 from hydrocarbon emissions, transportation of compressed CO2 from the source to the field, and injection and storage of CO2 into the subsurface.