Fracture stimulation fundamentals

Abstract

This article highlights the multi-disciplinary nature of multiple fractured horizontal wells in unconventional oil and gas reservoirs. The drilling, geomechanics, reservoir, completion, fracture stimulation, and field execution/operations disciplines must all do their jobs effectively in order to achieve success. Failure in any one discipline likely means project failure. The critical importance of multi-disciplinary success is clearest when you look at the competing objectives of horizontal well fracturing. All of the disciplines can and should work together to develop a horizontal well(s) project objective based on economics, deliverability, and/or estimated ultimate recovery; however, the geomechanics of the project will have a strong impact on whether the project objectives are achieved.The geomechanics need to be considered with respect to the stress state and its impact on hoop stresses and breakdown pressures (critically important to the drilling, completion, and fracture stimulation disciplines). Fracture interference must be considered to determine its impact on fracture width and treating pressure (critically important to the completions, fracture stimulation, and operational disciplines). In addition, the geomechanical effects on the fracture stimulation design and ultimately fracture geometry must be considered when stimulating a transverse horizontal well. From a fracture design perspective, material sourcing of the fracturing fluid (gel or treated water) is primarily a geomechanical issue in unconventional reservoirs, as is the type, size, and concentration of the proppant to be used. Even the designed fluid and proppant volumes should be based on the unconventional reservoir's rock and geomechanical considerations.This article will review some of the multidisciplinary inputs and objectives for multiple fractured transverse horizontal wells in unconventional oil and gas reservoirs. The paper will establish horizontal well fracturing design fundamentals and objectives that include determination of reservoir permeability, geomechanical parameters such as the in-situ stress state, the geomechanical basis of fracture design, and material sourcing. More importantly, this paper shows how rock and geomechanical considerations including fluid and proppant type and volumes can be utilized to design fracture stimulations in unconventional oil and gas reservoirs.