The primary purpose of surfactants used in stimulating Sandstone reservoirs is to reduce surface tension. Conventional surfactants adsorb rapidly within the first few inches of the sandstone formations, thus losing their effectiveness as the treating fluid leaks off. This results in trapped fluids and poor post fracturing fluid recovery. A surfactant solvent system in the form of a microemulsion can also be used to not only lower surface tension at very dilute concentrations, but alter contact angle and lower capillary pressure to further improve recovery. The unique microcells are also effective in controlling leakoff.
This study describes the laboratory experiments and field case studies of various surfactants used in the oilfield. Several surfactants including an ethoxylated linear alcohol, a nonyl phenol ethoxylate and a microemulsion system were investigated to determine their adsorption properties when injected into laboratory sand packs. Laboratory studies were also conducted to compare the leakoff and water recovery properties from gas wells.
Field data collected from Bradford and Speechley sandstone formations confirms experimental sand pack and core flow investigations. Reservoirs treated with microemulsion fluids demonstrate exceptional water recoveries when compared with conventional surfactant treatments. Wellhead pressures, flowing pressures and production data were collected and evaluated using a production simulator to show effective fracture lengths and drainage areas with various fluid systems.
Lab and field data collected in these studies from Appalachian Basin reservoirs illustrates that the addition of a microemulsion to a fracturing fluid exhibits significant advantages over the conventional surfactant treatments when water recovery, increased effective fracture length and well productivity are of concern to the operator.