Formation damage is a by-product of drilling, completion and production process and is attributed to many factors. In open-hole (OH) and cased-hole (CH) wells, hydrocarbon flow may be impeded by various damaging mechanisms caused by drilling and completion fluids, in-situ emulsions, water block, organic deposition and oily debris left downhole.
Mesophase fluids have been successfully developed to effectively resolve the persistent problem of near-wellbore damage. The physical-chemical properties of the mesophase systems include high oil solubilization, high diffusion coefficients through porous media and the reduction of interfacial tension between organic and aqueous phases to near zero, making them excellent candidates for removing formation damage. The chemistry of mesophase fluids makes the systems excellent choices for superior synthetic or oil-based mud (S/OBM) displacements in casing and for OBM filter cake cleanup in open-hole completion applications.
Mesophase fluids are thermodynamically-stable, optically transparent solutions composed of two immiscible fluids. They differ from ordinary emulsions because they can be prepared with little or no mechanical energy input. They are typically composed of a non-polar or oil phase, an aqueous phase, surfactant(s) and an optional co-surfactant. Depending on how they are formulated, they can exist in a single-phase or in a three-phase system, in which the middle-phase microemulsion is in equilibrium with excess water and oil. The formulation characteristics, phase type, and ultimately, the cleaning efficiency of a microemulsion is dictated by the hydrophilic-lipophilic balance between the surfactant(s) and the physico-chemical environment. The microemulsions described in the study are single-phase where oil and water are co-solubilized by the surfactant(s) and co-surfactants. The water/oil interface has a zero or near-zero curvature, indicative of the bicontinuous phase geometry that produces very low interfacial tension and the rapid solubilization of oil upon contact.
The formation of a mesophase does not ensure the fluid will solubilize oil effectively to leave surfaces water-wet. The mesophase behavior and cleaning efficiency can be altered by salinity, surfactant, co-surfactant, oil type, temperature and particulates. No two wells are identical and the physical and chemical conditions can vary greatly depending on the application. As a consequence, robust, optimized formulations are necessary and validation testing is required to determine the efficacy of a mesophase for a specific application, i.e., OBM displacement/cleanup and removal of formation damage in open-hole and cased-hole wells.
This paper presents a technical overview of mesophase technology and field applications that demonstrate the efficiency of mesophase fluids for removing S/OBM debris and filter cakes, reducing near-wellbore damage and improving well productivity.