A Novel Application of Closed-Fracture Acidizing
- Maysam Pournik (University of Oklahoma) | Hisham A. Nasr-El-Din (Texas A&M University) | Mohamed A. Mahmoud (Texas A&M University)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- February 2011
- Document Type
- Journal Paper
- 18 - 29
- 2011. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 3.2.4 Acidising, 1.6.9 Coring, Fishing
- acid fracturing
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- 1,231 since 2007
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The success of acid fracturing depends on the conductivity created and retained under closure stress in addition to the length of conductive fracture. The majority of acid-fracturing treatments show a sharp decline in conductivity with increasing closure stress, with almost no significant conductivity after a short production time. As a result, many wells are refractured to restore them to the original productivity after the initial fracture. However, the success of these refracture treatments has been diverse with respect to extent of stimulation.
A new approach to overcome productivity decline of acid-fractured wells is to perform closed-fracture acidizing (CFA) at the appropriate time in the life of the well to keep fractures conductive. An experimental study was conducted to investigate the effect of CFA on already-acid-fractured cores exposed to a certain level of closure stress. Indiana limestone cores were acidized with a typical acid system of 15 wt% hydrochloric acid (HCl) viscosified with a polymer under typical field conditions. After the first acidizing process, conductivity measurements were conducted on acid-etched core faces up to a certain closure stress. While the fracture was kept under the closure stress, a CFA treatment was conducted under the same conditions as the initial acidizing. The re-etched fractures were once again placed under different levels of closure stress, and conductivity measurements were taken at each stress. Experiments were conducted under different conditions of leakoff, polymer concentration, and closure stress after the first acidizing in order to determine the influence of these parameters on the refracturing conductivity.
In all cases, CFA enhanced fracture-face etching, while it significantly increased fracture conductivity under closure stress. However, leakoff, polymer concentration, and closure stress did influence the degree of success of CFA. Leakoff allowance and lower polymer concentration resulted in the most enhanced fracture conductivity in comparison to the initial acid-fracturing process.
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