Surfactants have long been used to prevent emulsions from limiting flow paths. Weak emulsifying surfactants (WES), however, create reverse oil-in-water emulsions. These emulsions solubilize oil and reduce interfacial tension between oil and water, allowing for increased mobility of oil molecules to be produced through laminated shales and small pore throat sizes. This paper evaluates the successful application of this technology to enhance oil recovery in the Wolfcamp formation.
A data set of 163 wells was selected in Reagan County, Texas. Within the data set, 43 wells were fracture stimulated with WES additives included. Variables, including sand/fluid volume, lateral length, and initial artificial lift method, were analyzed to compare the estimated ultimate recovery (EUR) of wells stimulated with and without WES. The data show that an increase in average EUR was achieved using WES.
Grouping wells by geological bench within the Wolfcamp shows varying results, with significant uplift in particular flow units. Differentiating the unique flow units of the Wolfcamp through log analysis provides clarity to the results. Two common challenges to long-term fracture conductivity are laminated reservoirs that pinch off as pressure declines and lower-permeability formations that experience creep. The mechanisms that restrict flow in each case can be partially mitigated by the ability of solubilized oil globules to flow through tighter pore throats. Additionally, oil globules that are mobilized because of reduced surface tension resulting from the use of WES yield higher recovery efficiencies within a given stimulated rock volume (SRV) than those without.
In addition to greater initial EURs, it has been observed that older producing wells that experience fracture interference by new wells using WES recover production rates more quickly than wells interfered by stimulation treatments not using WES. In some cases, additional reserves are added to older wells that experience hydraulic communication with WES; whereas, wells without WES-included stimulations are less likely to add reserves with hydraulic communication. This suggests that the mechanism for added reserves might not be limited to additional SRV but include a higher recovery factor from the trapped oil molecules that are mobilized by WES.