Minimizing formation damage is an important parameter to be considered to have expected production rates. Formation damage can happen at any phase during drilling, completion or production and is attributed by too many factors. Formation protection is critical while drilling the production zone because damage to the formation can adversely affect the well's production potential. This pay zone damage is minimized with the use of drill-in fluids, specialized fluids for "drilling in" and protecting oil/gas production formations. Damage to the pay zone, including fine solids migration into the formation permeability channels, in-situ emulsions, water block, organic deposition, oily debris, clay swelling within the formation pore spaces and irreversible reactions with invading polymers, reduce the average permeability of the formation, resulting in lower production rates. Most formation damage caused by conventional drilling fluids is by fluid invasion containing barite, finely ground drill solids and/or weighting material. The formation damage is even more critical in horizontal/inclined wells where the reservoir exposure is more and production rates are high.
Micro-Emulsion fluids are thermodynamically stable, optically transparent solutions comprising two immiscible fluids. They differ from ordinary emulsions because they can be prepared with little or no mechanical energy input. Micro-Emulsions typically comprise a non-polar or oil phase, a polar or aqueous phase, surfactant(s) and an optional co-surfactant. Depending on how they are formulated, micoemulsions can exist in a single-phase or in a three-phase system, in which the middle-phase microemulsion is in equilibrium with the excess water and oil. The formulation characteristics, phase type, and ultimately, the cleaning efficiency of a microemulsion are 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 Micro-Emulsion behavior and cleaning efficiency can be altered by salinity, surfactant, co-surfactant, oil type, temperature and particulates. A robust, optimized formulation is necessary and validation testing is required to determine the efficacy of a micro-emulsion for a specific application, i.e., OBM displacement/cleanup and removal of formation damage in openhole and cased-hole wells.
Micro-Emulsion fluids were successfully developed to effectively resolve the persistent problem of near-wellbore damage. The physical-chemical properties of the micro-emulsion 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 Micro-Emulsion 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 openhole completion applications.
This paper presents a technical overview of micro-emulsion technology and field applications that demonstrate the efficiency of Micro-Emulsion fluids for removing S/OBM debris and filter cakes, reducing near-wellbore damage and improving well productivity.