Economic Analysis for Enhanced CO2 Injection and Sequestration Using Horizontal Wells
Authors: Gui P. , Jia X. , Cunha J.C. , Cunha L.B. 
Published: March 2010

Abstract
Carbon dioxide flooding has been recognized widely as one of the most effective enhanced oil recovery processes applicable for light to medium oil reservoirs. Moreover, the injection of CO2 into an oil reservoir is a promising technology for reducing greenhouse emissions while increasing the ultimate recovery of oil.
Numerical reservoir simulation is an important and inexpensive tool for designing EOR CO2 projects and predicting optimal operational parameters. In this work, reservoir simulations performed with a compositional simulator were applied to investigate the macroscopic mechanisms of a CO2 injection process. Horizontal injectors were used to increase injectivity. Compared to traditional vertical wells, horizontal wells are more attractive to improve CO2 flooding economics by increasing injection rate, improving areal sweep and increasing CO2 storage. The effects of several important parameters on the performance of the CO2 process were studied to optimize the process. Operational parameters such as different production schemes, the injector pressure and injection rate were investigated to determine the optimal - operating conditions for simultaneous objectives of higher recovery and higher CO2 storage.
The application of CO2 flooding using horizontal wells can shorten- project life, which is critical to its economics. The simulation results served as the basic input parameters for the economic analysis performed. Furthermore, net present value (NPV) and profitability index results were used to optimize the profitability of the project and to compare the CO2 application using vertical and horizontal wells. The analysis used actual design parameters, including equipment and operating costs. The evaluation emphasized the importance of reservoir characteristics, optimum design of operation parameters and economic factors in the economic feasibility of CO2 injection projects for enhanced oil recovery and sequestration.

Introduction
The carbon dioxide flooding process can increase oil recovery by means of swelling, evaporating and lowering oil viscosity(1, 2). Many injection schemes using CO2 have been applied(3), including CO2 gas injection (continuously), CO2 gas slug followed by water, and others. There are some important factors to be considered during the design of CO2 flooding, including the availability and amount of CO2 to inject, the reservoir conditions, whether mobility control techniques are required and other general operating conditions(4, 5). Among these factors, the knowledge of reservoir conditions is essential to the injection/production process and, thereafter, the economic success of the project. These include the reservoir temperature and pressure, reservoir permeability and porosity, fractures and faults, etc. Field tests of CO2 floods have shown that reservoir heterogeneities, such as fractures, strata discontinuities and pinch-outs, can reduce the effectiveness of the process. CO2 is a highly mobile fluid because of its low viscosity, so fingering and channeling of CO2 or bypassing of oil can affect the volumetric sweep efficiency in CO2 flooding. In this case, mobility control becomes an important issue for the improvement of CO2 applications(6).
With the increase of productivity performance and the decrease of drilling and completion costs, horizontal wells became more cost effective. This paper compares the conventional CO2 flooding process using vertica