Saturation changes resulting from leakoff during stimulation treatments reduce the relative permeability to hydrocarbons in the invaded zone. Historically, surfactants have been added to stimulation fluids to lower the surface tension of the fluid in order to facilitate cleanup and mitigate formation damage caused by the filtrate, and this approach has become dogma. This paper, while recognizing the importance of low surface tension, focuses primarily on enhancing cleanup by altering wettability. Few studies have been performed to investigate the impact on cleanup resulting from use of surfactants to change formation wettability.
A rapid screening test has been devised to measure the effect that various additives, when added to aqueous fluids, will have on a synthetic core. The effect is determined by measuring the rate at which the fluid, with and without additives, is imbibed into a synthetic core. This rapid screening test has proven to be quite effective, in that it is simple, quick, inexpensive, and, above all, accurate. A further advantage of this method is that it provides a simple method to estimate contact angles and, therefore, provides a good measure of wettability. The simple imbibition test method has been validated by comparing the results from these tests with the results from sophisticated coreflow experiments. Results were further confirmed by greater than 40 successful treatments in the field.
In addition to cleanup performance, the research presented here focused on the environmental impact of the stimulation fluid. The ultimate outcome of the project was a stimulation fluid that performs in a superior fashion while meeting US Environmental Protection Agency (EPA) environmental requirements for offshore discharge in the Gulf of Mexico.