Foams for Effective Gas Blockage in the Presence of Crude Oil

Abstract

Abstract A study of foams for possible application in a new process with a potential for improving production from thin oil rims by formation of effective barriers against gas coning is reported. A total of 48 foaming agents for aqueous and non-aqueous systems have been evaluated using a gas-blockage test, as well as bulk foam stability tests and measurements of relevant surfactant properties. All experiments were performed in contact with sea water and crude oil at elevated temperature. In the gas-blockage test, foam is generated in 2-m long, 8.5-µm2 bead packs by constant-pressure displacement of a surfactant solution by gas at residual oil saturation. Stabilized gas rates through the foam-filled glass-bead pack are subsequently measured as a function of stepwise increasing pressure gradients. Only 4 foams were found capable of reducing gas permeability to the order of 0.1 µm2 or lower, at pressure gradients of 1 to 5 bar/m. These four products were found to be effective also in long-term tests at a constant pressure gradient of 1.5 bar/m. A number of foams known to be efficient gas-blocking agents in oil-free media were non-blocking in presence of residual oil. Bulk stability could not predict the gas-blocking ability for the foams studied. Further, no correlation was found between foam gas-blocking ability and the interfacial tensions, spreading conditions, oil saturation, foam quality, surfactant oil solubilization, or relative wetting abilities of surfactants measured. The four successful products found are fluorinated surfactants, from three different manufacturers, and were effective at 0.5 to 1 wt% concentration. Several fluorinated surfactants failed the gas-blockage test. Possible relations between observed gas-blockage performance and other properties are discussed. The phenomena involved appear to be complex and no clear relation between surfactant properties and foam performance has been found. Speculation is offered on what may be the controlling factors for foam gas-blockage efficiency.