A New Technique for Rapid Estimation of Fracture Closure Stress When Using Propellants

摘要

Minifracs are used to assist with main hydraulic fracturerndesign by generating estimates of the fluid efficiency, closurernstress, fracture geometry, and leakoff coefficient prior to thernmain treatment. Closure stress is frequently determined byrnanalyzing the pressure falloff response after pump shut-downrnusing a Nolte G-Function analysis plot. Comparison of thernmeasured data with the dimensionless Nolte G time indicatesrnclosure when used in combination with the derivative andrnpressure superposition derivative.rnDuring perforating/propellant treatments of wells, the usernof a high-speed downhole digital pressure data recorderrnenables a new rapid technique for determining closure stressrnusing the G-Function and associated methods. The propellantrnevent breaks down the perforations and extends fractures intornthe formation in the time span of tens of milliseconds, and canrnthus be treated as a high-speed minifrac. The analysis methodrnand feasibility of this new technique are demonstrated.rnThe falloff pressure curve after a propellant event,rntypically lasting no more than a few hundred milliseconds, isrnshown in several case histories to provide sufficient closurerninformation. Where these data are available, results arernconsistent with other methods. Although certain favorablernconditions must exist for the method to be applicable, this newrntechnique can be used where a quick estimate of closure stressrnis needed prior to hydraulic fracturing and while equipment isrnin place in the field. Work continues to fully define the rangernof applicability and accuracy of the new technique.