Carbon Dioxide Well Stimulation: Part 2 -- Design of Aminoil's North Bolsa Strip Project (includes associated papers 11928 and 12234 )
Authors: Patton John T. , Sigmund Phil , Evans Brian , Ghose Shanu , Weinbrandt Dick 
Published: December 2007

A CO2 stimulation process has been designed for heavy-oilreservoirs. The process will be applied by Aminoil U.S.A. in their North Bolsa Strip lease of the Huntington Beach field. High oil viscosity (177 cp) and severe faulting have caused poor performance in early attemptsto waterflood this reservoir. Each producing well is to be treated with 2 to 10 tons of CO2 per foot of net pay. Gases produced are separated cryogenically to produce saleable hydrocarbons and reusable CO2. The processing also eliminates possible emissions that might affect air quality. CO2 is reinjected to improve economics.

Introduction

Work in the early 1950's by Jersey Production Researchco., Pure Oil CO., and Oil Recovery Corp. identified the potential for using CO2 as an enhanced oil-recovery agent. However, during those early years, the cost of CO2 usually was greater than the price of crude oil, and there was no incentive to commercialize the process. The escalation of incentives, both economic and political, during 1979-80 prompted Aminoil to examinethe possibilities of using CO2 to enhance the recovery of petroleum.

It is well recognized that CO2 used to displace oil under miscible conditions represents the ultimate inreducing residual oil saturation in the swept portion ofthe reservoir. Residual oil saturations as low as 5% areobtained easily in the laboratory. Intuitively, recovering most of the oil in the swept region should bethe ultimate goal of a recovery process. Hence, most of the developmental work in the past decade was focused on laboratory and field demonstrations of the miscibledisplacement process. The pioneering effort of Chevronand others at Sacroc, the first commercial CO2 application, represents a significant advance in the art. Because of the great diversity with respect to crudeoil properties and reservoir depth, there are many reservoirs, mostly viscous oil, not amenable to the miscibledisplacement process. The same high incentives apply tothese reservoirs, and this has given rise to rapidly expanding laboratory and field programs to enhance oilrecovery by CO2 under immiscible conditions. The results of these studies on immiscible displacement of viscous crudes have been enlightening. Although immiscible CO2 flooding cannot reduce the residual oil saturation significantly, many candidate reservoirs contain such high initial oil saturations that total recovery-barrels of oil transferred from the reservoir to the stock tank-can exceed the high recoveriesthat characterize the miscible process. The work ofBeeson and Ortl off involving linear laboratory cores demonstrated that the total barrels of oil recovered incremently over waterflood as well as the barrels of oil recovered per thousand cubic feet of CO2 injected were comparable for the two processes. Recent laboratory experiments seem to confirm these earlier results, and at least two companies, Phillips and Champlin Petroleum, are operating field projects involving immiscible CO2flooding. Considering the outstanding success of the huff'n'puff single-well steam stimulation process, it seemed possible that similar technology could be successful with CO2. Preliminary field experiments supported by computer simulation show that, under optimal conditions, single-well stimulation with CO2 may indeed be commercial. The profitable range of oil saturations and viscosity aremore limited than for steam, and, hence, the successratio is expected to be lower. More selectivity and better engineering are necessary to achieve an attractive payout of the higher investment associated with the CO2 process.

JPT

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