A new method for screening surfactants for foam diversion applications

Foam diversion is a promising method for diverting acid to formations that would otherwise be bypassed Even though numerous surfactants are being used by the stimulation service companies, there is no reliable or easy-to-use method for screening them. A standard method is proposed in this article. T he method is validated with laboratory diversion tests conducted under high -pressure conditions using Berea sandstone cores. Seven different prescreen ed surfactants were selected for testing the proposed method. Several screening methods have been proposed in the past including static t ests and porous media tests. However they are neither dependable nor standa rd. Therefore, a new screening technique was developed in which optimum val ues of parameters, such as ultimate liquid recovery, recovery at breakthrou gh, cumulative liquid produced to cumulative air produced ratio (L/A), liqu id injection pressure ratio (P2/P1), and breakthrough time during the porou s media tests, were used to select the surfactants that are most likely to help diversion. Based on the new surfactant screening criteria, the overall ranking (from best to worst) of the seven surfactants used in this article was as follows: S3 --> S8 --> S2 --> S6 --> S4 --> S1 --> S5 Among these seven surfactants, four surfactants were selected for further e valuation under high-pressure diversion conditions. Diversion tests were co nducted using four different permeability contrast values. This was the fir st time a screening criterion was tested against diversion results that wer e performed under high pressure and low-permeability conditions. The rankin g of the screening criterion held true for the diversion tests. In order to validate the proposed screening criterion further, foam diversion results were obtained in the presence of residual oil. It was found that the presen ce of residual oil changed the ranking in the high-pressure diversion case. In the presence of oil, the ranking of the diversion tests was exactly the same as that determined by the screening criterion. The screening method i s, therefore, proposed as a standard for selecting surfactants for diversio n purposes.