A New EOR Method

Abstract

Abstract A new method of enhanced oil recovery has been developed and applied to a sector simulation using some of the data from the South Slattery Field, Minnelusa A reservoir. The new method, termed ASPaM, combines features of CO2 miscible flooding with Alkaline-Surfactant-Polymer (ASP) flooding to produce an enhanced WAG flood. A numerical pre-processor program had to be developed to produce the required mixing zone properties of a CO2 front, which are input to the CMG simulator, STARS. STARS is a chemical flood simulator, but cannot accomodate the solvent model. The pre-processor calculates oil and solvent properties based on the Todd-Longstaff procedure. Sensitivity analysis showed this new method can give a much better recovery in comparison to ASP or CO2 WAG flooding for different depositional environments. ASPaM benefits from high micro and macro sweep efficiencies plus miscible flooding, even for a small ASP slug size. The simulation results revealed the recovery from this scheme is considerably better than ASP and CO2 flooding separately. It showed the recovery can be improved and accelerated by the application of ASPaM, and its performance is a function of the miscibility of the CO2-oil miscible zone and the reduction in IFT at the ASP-oil interface at reservoir conditions. Moreover the water/gas ratio of ASPaM is totally different in scale compared to a typical WAG scheme. A significant acceleration and improvement in recovery is achieved with a 10 % pore volume ASP slug size. This work indicates CO2 flooding and sequestration can be stabilized and enhanced if it combines even with a small ASP slug size. The results so far have been very encouraging. Introduction Carbon dioxide has been used for enhanced oil recovery (EOR) purposes since the 1950's (Izgec et al, 2005). Research on the use of CO2 for EOR continues with ever growing interest; however, research concerning terrestrial sequestration of CO2 for environmental purposes is relatively recent (Jessen et al, 2001). The CO2 can make up multi-contact and first contact miscibility with oil at reasonable reservoir pressures while other miscible gases may not reach this point for up to a couple of thousand psi more. Although the microscopic sweep effciency of carbon dioxide flooding is good, its macroscopic sweep effciency is relatively poor due to phase segregation and unfavorable mobility ratio. However, the WAG gas injection scheme was originally proposed to tackle this shortcoming, mainly by using the water to control the mobility of the displacement and to stabilize the front.