Case Histories: Frac Fluid Recovery Improvements of Appalachian Basin Tight Gas Reservoirs

Paktinat, Javad, Stoner, Bill, Williams, Curt, Pinkhouse, Joe

Universal Well Services,159 Northwood Drive, Meadville, PA 16335

The primary purpose of nonionic surfactants used in stimulating Sandstone reservoirs is to reduce surface tension, contact angle and emulsion tendencies.  However, many of these chemicals adsorb rapidly into the sandstone formation, reducing their effectiveness of post frac fluid recovery.

 This study describes the laboratory experiments and field case studies of various surfactants used in the oilfield. Several different surfactants including ethoxylated linear alcohol, nonyl phenol ethoxylate and a microemulsion system were investigated to determine their adsorption properties when injected into laboratory sand packed column. A laboratory simulated comparison study of ethoxylated surfactants and microemulsion was used to identify their water recovery properties from gas wells.

Field data collected from Benson, Balltown, Injun, and Speechley sandstone formations confirms experimental sand packed column and core flow investigations. Reservoirs treated with microemulsion fluids demonstrate exceptional water recoveries when compared with conventional non-emulsifying surfactant treatments.  Wellhead pressures, flowing pressures and production data were collected and evaluated using a production simulator to show effective frac lengths and drainage areas with various fluid/surfactant systems.  These investigations and presented case studies can be used to optimize chemical treatments.  The primary objectives of this study include:

1.        Comparison studies of the microemulsion system with conventional ethoxylated surfactants commonly used in the oilfield to determine their adsorption properties into the proppant pack, surface tension and water recovery.

2.        Experimental data comparing effectiveness of conventional surfactants and microemulsion in non-emulsification, regain permeability, and fracture clean up test.

3.        Case studies and production simulations where microemulsion treatments have improved water recoveries in treated gas wells of Benson, Balltown, Injun, and Speechley formations.

Field data collected from several gas wells stimulated in Appalachian Basin reservoirs illustrates that the microemulsion added to frac fluid exhibits significant advantage over the conventional surfactant treatments when water recovery and increased effective frac length and well productivity are of concern to the operator.