Overcoming OBM Filter Cake Damage Using Micro-Emulsion Remediation Technology across a High-Temperature Formation

Abstract

Abstract Formation damage is one of the main concerns at various stages of drilling, completion and production processes and is attributed to many factors. Either in open-hole or cased-hole completed wells, hydrocarbon flow in the reservoir may be impeded by various damaging mechanisms such as in-situ emulsions, water block, organic deposition and oily debris left downhole. Micro-emulsion fluids are thermodynamically stable, optically transparent solutions of two immiscible fluids formulated with a specialized surfactant blend and/or co-surfactant. They differ from normal emulsions because they can be prepared with little or no mechanical energy input. They typically comprise a non polar (oil) phase, a polar (aqueous) phase, surfactant(s) and an optional co-surfactant. Depending on how they are formulated, mesophase fluids can exist in a single-phase or in a three-phase system wherein the middle-phase microemulsion is in equilibrium with excess water and/or 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 this 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 micro-emulsion alone does not ensure the fluid will solubilize oil effectively to leave surfaces water-wet. The micro-emulsion behavior and cleaning efficiency can be influenced 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 openhole and cased-hole wells. Micro-emulsion fluids were successfully developed to effectively resolve the persistent problem of near-wellbore damage. The physico-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 filtercake cleanup in openhole completion applications. This paper presents a technical overview of micro-emulsion technology and field application in a high- temperature gas environment that demonstrate its efficiency in removing Non-Aqeuous Fluid (NAF) debris and filter cakes, whilst reducing near-wellbore damage and improving well productivity and solids mobility.