The main challenges for extra low permeability reservoir are injectivity decline and high tubing head pressure (THP) which caused the decreases in hydrocarbon production. The most common causes of deterioration in the reservoir permeability and formation damage include the buildup of in-situ emulsions due to crude oil interaction with drilling and completion fluids, water blockage, asphaltene and paraffin deposition and alteration of near-wellbore wettability. In new wells, near-wellbore formation damage may be caused by emulsion blockages when the whole mud, mud filtrate or completion fluids interact with the formation fluids.
Traditional chemical treatments have been widely used to remediate damaged formations for removal of non-aqueous fluid. Various approaches to tackle this problem have been adopted. For example, acid, solvents and mutual solvents have been applied to improve the reservoir permeability, with varying degrees of effectiveness. Microemulsion fluids with unique propertie such as an ultra-low interfacial tension (IFT), high solvency and compatibility with formation fluids has received great interests and shows great potential to effectively remove emulsion blockages, remove precipitated crude oil macromolecules, and reverse wettability to enhance hydrocarbon production.
In this paper a new in-situ microemulsion formulation consisting of blend of anionic-cationic surfactants (Sa/c) has been developed to assist the fluid recovery for extra low permeability reservoir at dilute concentrations. Ultra low IFT of 3×10−4 mN/m, solubilization parameters of 18, and ultra low critical micelle concentration of 6.8 mg/L were obtained. Freezing point of crude oil was decreased by 18%, together along with 84.5% viscosity reduction by formation of microemulsion. In addition, wettability alteration was also observed.
Lab data shows that the in-situ microemulsion is highly effective in fluid recovery and relative permeability enhancement when applied in stimulation treatments at dilute concentrations.
Filed test by using in-situ microemulsion-assisted fluid recovery with Sa/c was tested in super high temperature-extra low permeability formations (reservoir temperature: 116°C, permeability: 4.5 mD) to demonstrate how this novel technology can significantly enhance hydrocarbon production in poorly producing wells.