The Greater Permian Basin includes both conventional and unconventional oil production. While Permian's conventional oil production (via primary, secondary, and enhanced oil recovery) has been very successful over the last half a century, the average primary oil production from its unconventional resource is about 5%. Because of the enormous remaining oil in the Permian, there is a need for formulating robust and cost effective EOR methods for the Permian unconventional production (e.g., Wolfcamp). This paper addresses this issue by providing insights into promising EOR mechanisms based on laboratory and field observations.
We conducted wettability alteration measurements for a typical surfactant and a simple mutual (oil-water) solvent in the Wolfcamp using a Drop Shape Analyzer (DSA) apparatus at reservoir temperature and pressure conditions. We also used these results to explain that wettability alteration, molecular diffusion, and component partitioning would result in improved oil recovery for Wolfcamp shale reservoirs. Similar EOR process applications and the associated mechanisms are the basis for the favorable outcomes of three recent field EOR pilot tests reported by other researchers.
Lab results also indicate that temperature significantly affects water-oil contact angle, while pressure has a minor impact. Mutual solvents show minimal contact angle change under standard and reservoir conditions. However, the effect of mutual solvents on improving oil recovery is based on a different mechanism that entails mass transfer due to mutual solubilization both in water and in the oil phase. For surfactants, even a small concentration notably change contact angles on the core surface and reduce IFT dramatically, especially in low-salinity solutions. Oil mobilization by surfactants is by wettability alteration and adsorption at the oil-water interface.
We present laboratory wettability alteration measurements using a very small concentration of a non-ionic surfactant and a mutual solvent for the Wolfcamp formation. The experimental results are used to explain why the use of low-concertation surfactants and specific mutual solvents enhances oil recovery via the perceived wettability modification. As indicated earlier, these laboratory results shed light on why three recently reported field pilot tests have shown great promise for cost-effective EOR in unconventional shale reservoirs.