Evaluation of a Surfactant: Steam-Soak Pilot Test in the Bolívar Coast, Venezuela

Abstract

This paper presents field test results of sixteen steam soaked wells in which the injected steam was treated with two different surfactants selected in the laboratory as being the most suitable to he applied under Bolivar Coast Conditions. The laboratory research was done by Shell Laboratorium (Netherlands) and Intevep-PDVSA Research Center (Venezuela) and the main selecting criteria was the pressure drop measured in the porous media during steam Foam Flow tests. The two steam Foam Formulations selected were, a long-chain alkyraryl toluene sulphonate (SURFACTANT 1) and a branch-chain alkyraryl benzene sulphonate (SURFACTANT 2). The SURFACTANT 1 was used in nine wells while the SURFACTANT 2 was injected in seven. The stimulation mechanism of SURFACTANT 1 seems to be steam diversion to the less produced sands and for SURFACTANT 2 it appears to be a change of interfacial properties in the water-oil-rock system. Although most of the steam foamed wells had not completed the production cycle, it can he concluded that 60% of them have presented positive response to steam foam. The initial oil rate response was equal to or slightly greater than that expected from a normal cycle, but steam Foamed wells produced up to three times the additional cumulative oil expected (75,000 bls vs. 25.000 bls for a third cycle). This is due to the fact that the decline of the oil production rate was lowered to about 12% pa. which is indeed close to that of primary production. The better oil production performances were obtained when the steam penetrated deeper into previously non productive layers. The maximum diversion registered was close to 90 feet as compared to 35 feet of the initial profile. Introduction Steam soak has proved to be a very efficient re-recovery process in the heavy oil reservoirs on the Bolivar Coast In Western Venezuela. The effectiveness of this method is intimately related to compaction which is the main production mechanism in these reservoirs. In order to minimise the benefits obtainable from this method the oil production should ideally come From all the sands of the reservoir. Nevertheless, the challenge of uniformly distributing the injected steam to each productive sand has been one of the greatest operational problems, At present selective injection is accomplished by the installation of special mechanical completion equipment, but this procedure complicates production operations thereby increasing costs. in order to enhance the steam injection profile and increase the recovery from heavy oil reservoirs, a programme was initiated to evaluate the use of foaming agents to reduce the mobility of steam. Laboratory tests carried out using values of steam quality, steam injection rates, pressure and temperature representative of the prevalent conditions in the Bolivar Coast, resulted in the identification of two appropriate surfactants. There upon a programme of field tests was initiated in Tia Juana, Lagunillas, and Bachquero in order to:Evaluate the capacity of the steam foam mixture to reduce the effective permeability to steam. P. 915^