| Popis: |
Minifracs are used to assist with main hydraulic fracture design by generating estimates of the fluid efficiency, closure stress, fracture geometry, and leakoff coefficient prior to the main treatment. Closure stress is frequently determined by analyzing the pressure falloff response after pump shut-down using a Nolte G-Function analysis plot. Comparison of the measured data with the dimensionless Nolte G time indicates closure when used in combination with the derivative and pressure superposition derivative. During perforating/propellant treatments of wells, the use of a high-speed downhole digital pressure data recorder enables a new rapid technique for determining closure stress using the G-Function and associated methods. The propellant event breaks down the perforations and extends fractures into the formation in the time span of tens of milliseconds, and can thus be treated as a high-speed minifrac. The analysis method and feasibility of this new technique are demonstrated. The falloff pressure curve after a propellant event, typically lasting no more than a few hundred milliseconds, is shown in several case histories to provide sufficient closure information. Where these data are available, results are consistent with other methods. Although certain favorable conditions must exist for the method to be applicable, this new technique can be used where a quick estimate of closure stress is needed prior to hydraulic fracturing and while equipment is in place in the field. Work continues to fully define the range of applicability and accuracy of the new technique. |
