Yates Field is a large, naturally fractured, carbonate reservoir in west Texas. The estimated recovery after 84 years of production since 1927 is about 35% after primary depletion, water and gas injections. Laboratory and field production data indicate that Yates is an oil-wet reservoir system. Consequently, it is expected that wettability alteration can improve Yates recovery by changing to more favorable water-wet condition. A field pilot with one injector and one producer using a new, anionic surfactant was performed in Yates to determine if the surfactant can improve oil production via lower interfacial tension and wettability alteration mechanisms. This paper shows a field case study of an integrated use of a geological model, reservoir simulator, tracer test data, and laboratory results to design a surfactant pilot in the fractured carbonate Yates Field. Reservoir simulation models were calibrated by matching the bromide tracer test results. The models were used to quantify the fracture properties and study different injection scenarios. The optimal schedule was to inject multiple cycles of a 3% surfactant, at a rate of 500 b/d for 12 hours, and then shut-in the injector for 12 hours. A total of 50,000 lb of surfactant was injected into the pilot area.

Surfactant residues (Tween 80 Esters and Tween 80 free Polyols) were determined in Maryland tobacco treated with a fatty-alcohol-type sucker-control formulation. The levels of residues in leaves decreased throughout the growing and air-curing periods, but decreased the most during the first 24 hours after treatment. Factors affecting Tween 80 residue levels included dosage and location of leaves on the plant.