New Technique Restores Initial Fluid Efficiency Observed in Mini-Frac and Results in Increased TSO Frac-Pack Success

Abstract

It has been observed that pumping a mini-frac prior to a TSO Frac-pack can impact the effectiveness of the frac-pack. The calculated fluid loss parameters determined in the diagnostic test are often not valid for the main fracture design due to the residual effect of the mini-frac and/or step-rate fluids. A technique will be presented in this paper which allows the calculated fluid loss parameters from the diagnostic test to be used reliably without excessive waiting time for the reservoir to recover to its original leak off characteristics. Fifty plus treatments were evaluated to develop a technique which makes this possible. The use of this technique resulted in a significant change in the success of the TSO designed treatments - success being a TSO type pressure increase while pumping. The success rate to achieve designed TSO, by incorporating the changes described in the paper, was increased over 20 percent with a reduction in time between diagnostic tests and the main frac. In the wells associated with this paper, a borate-crosslinked fluid was used for a mini-frac treatment followed by a step-rate test prior to the main proppant laden frac-pack. The fluid was designed with minimal polymer loading for the well conditions. The resulting mini-frac tests had low fluid efficiencies. It was originally thought that using this fluid, followed by injection of a linear step-rate fluid, would minimize the changes observed in fluid efficiency between the diagnostic test and the main fracture treatment. However, the effect of the diagnostic test on fluid leak off still resulted in less than desired TSO predictability. A technique of adding a pH control additive into the final portion of the step-rate test fluid was found to successfully allow the use of the observed diagnostic test results, honoring the efficiency from the mini-frac test. The quantity and placement of the pH control agent in the step-rate protocol were dependent upon well conditions. The waiting time between the diagnostic test and the main treatment was reduced since a positive, controlled change was applied. The optimum pH reduction for the desired effect was determined in the laboratory and designed into each treatment depending upon well conditions.

Frac Packing: Best Practices and Lessons Learned From More Than 600 Operations

“…Therefore, it results in a higher success rate for TSO during the main frac-packing treatment and a higher net-pressure gain for treatments. Using a pH-control-additive technique could result in 60% higher net-pressure gains than in treatments without a pHcontrol additive (Holcomb et al 2002).…”

“…The injection fluid during minifrac tests could affect the leakoff characteristics of the main frac-packing treatment (Bruce and Jacot 2000;Smith et al 2000;Holcomb et al 2002). This effect should be considered for the main-treatment design with the proper software (Bruce and Jacot 2000).…”

“…The analysis of surface-pressure data (pumping pressure) does not always provide an accurate determination of closure pressure, closure time, leakoff coefficient, and fluid efficiency for cases with high leakoff and fast closure times (Neumann et al 2002). However, "live-annulus" pressure readings will provide an accurate estimation of the aforementioned parameters (Holcomb et al 2002;Neumann et al 2002;Hale et al 2004).…”