Steam Alternating Solvent Process: Lab Test and Simulation

Abstract Stimulation of carbonate formations by acid dissolution of the rock has been an efficient and successful method of bimproving production in oil and gas wells. Hydrochloric acid is the normal fluid of choice. However, in high temperature applications corrosion issues limit usage, especially in chrome completions. Acetic acid has been used with some success and with adequate corrosion protection. But due to its low reactivity at higher temperatures, the efficiency with which a gallon of acid dissolves the formation is perceived as low. This perception comes from reaction efficiency of acetic acid reported in the literature ranging in values from 90% at 25 °C to 40% at 121 °C for 2 to 15 wt%, respectively. Acetic acid reaction on calcium carbonate is controlled by its small dissociation constant, 1.754E-05 at 25 °C (77 °F) and therefore is labeled a weak acid. Abstract A new heavy oil recovery process, Steam Alternating Solvent (SAS) process, is studied by lab experiments and corresponding numerical simulation. The SAS process involves injecting steam and solvent alternately, using well configurations similar to those in the SAGD process. This process is designed to combine the advantages of the SAGD and Vapex processes to minimize the energy input per unit oil recovered. Lab experiments were conducted using a 2-D highpressure/ high-temperature model. One baseline SAGD test and one SAS test were performed using oil sample from Cold Lake region. Mixture of propane and methane was used as the solvent in the SAS test. The results showed that the energy input in the SAS process was 47% lower than that of the SAGD process, for recovering the same amount of oil. The post-run analysis revealed that asphaltene precipitation occurred in the porous medium. Numerical history matching of the test data using CMG's STARS reservoir simulator captured the main features of the process. Introduction The main obstacle to produce oil from the large deposits of heavy oil and bitumen resources in northern Alberta is the high viscosity of these oils, usually over 10,000 mPa?s at reservoir conditions. There are generally two types of methods for the reduction of oil viscosity. The first is to increase oil temperature by injecting a hot fluid, such as steam, into the reservoir, or by in situ combustion through injection of oxygencontaining gas. The second method is to dilute the viscous oil by injecting low viscosity hydrocarbons (solvent). As the solvent dissolves and mixes with the viscous oil, the low viscosity solvent-diluted oil can then be recovered. Two processes, Steam Assisted Gravity Drainage (SAGD) and Vapor Extraction (Vapex), have been developed for the recovery of heavy oil and bitumen resources (1, 2, 3) based on the combination of the above viscosity reduction methods and the horizontal well technology. The first has been successfully tested in the field and is moving to commercial scale application (4, 5). The second is presently in the initial field-testing stage (6). The advantage of the SAGD process is its relatively higher oil production rate. However the higher production rate is associated with excessive energy requirements, CO2 generation, and post-production water treatment. The Vapex process has the advantage of lower energy consumption, therefore, less CO2 generation. The major drawback of the Vapex process, however, is its relatively lower oil production rate. In the past several years, modifications, such as ESSAGD (7) and SAGP (8), have been proposed to improve SAGD's energy efficiency. In the ES-SAGD process,

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