Single Well Campain Exposes Substantial Opportunity in Barrancas High-Temperature High-Salinity Formation

Chemical EOR is at the edge for high temperature and high salinity, reservoirs. Further challenges appear in these reservoirs such as mixed-wettability, clays with a high content of divalent ions, mid to low permeability, injectivity problems for surfactant and polymers. Nevertheless billions of barrel remain in Barrancas Formation at 98–105 C and 65–85 g/L as TDS (2.2g/L to 3 g/L divalent ions) with some anihidrate content. The usual approach for this type of reservoirs has been to develop alkali-surfactant-polymer formulation with softened water and standard HPAM. However, water desalinisation-softening is very challenging to implement because of economics, environmental and logistic restriction to desalinisation-softening waste disposal. Instead, we targeted the actual water conditions to design the surfactant-polymer cocktail. We collected fluid samples from the six reservoirs producing from Barrancas Formation, and we obtained the equivalent alkane carbon number for each crude oil. An automated robotic platform assisted the formulation screening process. We coreflood outcrop samples to test surfactant polymer performance and multiple samples from three of the six reservoirs restoring wettability. Then, we implemented three single well tracer test with different formulations in the three major fields of Barrancas Formation. We used a new generation of traces manufactured by Restrack which allowed us to obtain a residual oil saturation distribution along the radial direction pre- and post-surfactant polymer injection. Knowing the saturation distribution along the radial direction can assist in the determining the interplay between adsorption, dispersivity, downhole temperature variation and optimal conditions of the surfactant cocktail. The three single wells also seemed to confirm mixed-wet wettability. Because of the residual oil saturation before surfactant-polymer was the equal independent permeability and reservoir quality/capillary desaturation curve. The three single wells recovered from 40% to 18% of the residual oil saturation based on an average volume calculation using the conventional tracers.

Further calculations using new generation tracers indicate that the recovery was affected by suboptimal conditions that vary along the radial direction, operative conditions during production phase that smooth-out traditional tracers. The data obtained by the new generation tracers indicated that the recovery could be locally higher than the conventional tracers calculations.

Adsorption in the single well tracer test was significantly lower than in corefloods (10 times smaller). Dispersivity indicated that for upscaling the surfactant performance to model interwell pilot a cell's size below 1 meter was needed. Alternating surfactant and polymer could improve injectivity of sulfonated polymer rather than simultaneous injection.