Well-Test Analysis Following a Closed-Fracture Acidizing Treatment

Sollman, Mohamed Y.; Hunt, J. L.; Daneshi, T.

doi:10.2118/17972-pa

Cited by 8 publications

(1 citation statement)

References 12 publications

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“…Wormholes increase the flow and oil and gas production from the reservoir by increasing the formation near the wellbore by several magnitudes and have a negative skin factor up to À4. [1][2][3][4][5] During the acidizing process, the injection rate is limited to keep the bottomhole pressure less than the fracturing pressure. [6] Successful carbonate formation acidizing depends on the selected acid systems.…”

Section: Introductionmentioning

confidence: 99%

A novel retarded HCl acid system for HPHT carbonate acidizing applications: Experimental study

Ibrahim

2021

Can J Chem Eng

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Retarded acid systems for high‐pressure and high‐temperature (HPHT) carbonate reservoirs are the key to provide a deep acid penetration and higher acid efficiency. The current study experimentally evaluates a new retarded HCl acid for HPHT carbonate acidizing applications. The acid retardation mechanism is attained by using a polymeric resin‐based composition that restricts the proton mobility of the acid species. Ten Indiana limestone cores were used with the dimensions of 6 in (0.15 m) length and 1.5 in (0.038 m) diameter and average permeability of 9 mD (0.009 0.25emnormalμm2). Two sets of experiments were conducted, one at 250°F (394 K) and another at 300°F (422 K), with acid injection rates from 0.5–10 cm3/min (8.3E−9 to 1.67E−7 m3/s). The pore volume of acid required to breakthrough (PVBT) was monitored. Effluent samples were collected to track the pH and the dissolved material. Computed tomography (CT) was used to scan the core before and after the experiment to determine the wormhole propagation along with the core. The optimum injection rate at 250 and 300°F (394 and 422 K) were found to be 2.5 and 6 cm3/min (1.67E−8 and 1.25E−7 m3/s) with PVBT of 0.41 and 0.43 PV, respectively. The 3D CT scan showed an effective wormhole profile featuring a single dominant trajectory with few branches. These results are confirmed by calcium ion concentration profiles through inductively coupled plasma (ICP) analysis. The use of the new acid system will provide deep penetration with low injected acid volume. As a result, the stimulation job efficiency will improve.

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Section: Introductionmentioning

confidence: 99%

A novel retarded HCl acid system for HPHT carbonate acidizing applications: Experimental study

Ibrahim

2021

Can J Chem Eng

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Acid Re-fracturing: Is it a Good Practice?

2009

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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. 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 re-fractured in order to restore back to the original productivity after the initial fracture. However, the success of these re-fracture treatments has been diverse with respect to extent of stimulation. The effect of re-fracturing on acid fractured wells has not been studied and the conditions that result in success or failure of re-fracturing operations are not understood. An experimental study was conducted to investigate the effect of re-fracturing on already acid fractured cores exposed to closure stress. Indiana limestone cores were acidized with a typical acid system of 15 wt% HCl acid 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 re-fracturing 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 taken at each stress. Experiments were conducted under different conditions of leak-off, polymer concentration and closure stress after the first acidizing in order to determine influence of these parameters on the re-fracturing conductivity. Acid re-fracturing enhanced fracture face etching, while significantly increased fracture conductivity under closure stress. However, leak-off, polymer concentration, and closure stress did influence the degree of success of acid re-fracturing. The refractured sample with leak-off and lower polymer concentration resulted in the most enhanced fracture conductivity in comparison to the initial acid fracturing process. Introduction Acid fracturing is a well stimulation process in which acid dissolution along the face of the hydraulically induced fracture is expected to create lasting conductivity after fracture closure. However, conductivity after fracture closure requires that the fracture face is non-uniformly etched by the acid while the strength of the rock is still maintained at high levels to withstand the closure stress. While the etched pattern has a dominant influence on the resulting fracture conductivity at low closure stresses, conductivity is more dependent upon the strength of fracture face asperities as the surface features along the fracture faces are crushed under higher closure stresses.

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A Novel Application of Closed-Fracture Acidizing

Pournik

Nasr‐El‐Din

Mahmoud

2011

SPE Production &Amp; Operations

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Summary 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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Well-Test Analysis Following a Closed-Fracture Acidizing Treatment

Cited by 8 publications

References 12 publications

A novel retarded HCl acid system for HPHT carbonate acidizing applications: Experimental study

A novel retarded HCl acid system for HPHT carbonate acidizing applications: Experimental study

Acid Re-fracturing: Is it a Good Practice?

A Novel Application of Closed-Fracture Acidizing

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