New Continuous-Mix Process for Gelling Anhydrous Methanol Minimizes Hazards

Abstract

Summary This paper discusses a novel approach to well stimulation with anhydrous methanol-based fracturing-fluid that significantly reduces hazards to personnel and equipment during the fracturing process. Research is presented on the various chemical and engineering process technologies used to develop and evaluate continuously mixed anhydrous methanol fracturing-fluid performance. Field case histories are also discussed. Introduction Since the development of hydraulic fracturing technology as a well completion technique hazardous fluids frequently have been used. These fluids include refined oils, formation condensates, crude oils, acids, alcohols, and a variety of other chemicals and additives. Batch mixing is a common technique used to formulate fluids for fracturing applications. The fluid viscosity is adjusted to the desired level by circulating the base fluid through blending equipment while adding the polymeric gelling agents, buffers, and other chemicals. The fluid must circulate through the equipment many times for the fluid to develop the desired viscosity. When hazardous materials are handled in a multiple-circulation process, the potential for accidents is high. Technological advances in recent years have provided sophisticated fracturing-fluid systems and field equipment, along with microprocessor systems that monitor and control the pumping treatment. These advances have been implemented without compromising the efficiency of the total operation. In many cases, the overall system performance improved significantly. For example, the development of oil-slurried polymer concentrates and polymer hydration units led to the widespread application of continuous-mix processes to mix fracturing fluids. The damage characteristics of any fracturing-fluid system are of paramount importance to successful reservoir stimulation. Formations that have low bottomhole pressure or contain significant concentrations of water-sensitive clays are typically candidates for stimulation with non-water-based fracturing fluids. Problems with clay swelling and migration commonly are encountered in formations containing significant amounts of smectite and illite-type minerals. The degree of formation sensitivity depends on the concentration and type of clay components, clay or mixed clay orientation in the pore channel, and the ion balance between connate water and clay minerals. In low-permeability formations, capillary forces can have a significant effect on production rate and total hydrocarbon recovery. Capillary forces increase proportionally with the surface tension of the formation fluid. When the capillary forces exceed the formation-fluid driving force, a water block may occur. The use of methanol has long been recognized as an effective technique to remove formation water blockage. The miscibility of methanol with formation fluids reduces surface tension, which promotes removal of the water block and enhances fluid recovery.