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

Abstract

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.

Mechanistic analysis of matrix-acid treatment of carbonate formations: An experimental core flooding study

“…Actually, it represents the density of the material. Higher CT number represents materials with higher density while lower CT number represents the materials with lower density [ 78 , 79 ].…”

Evaluation of the effectiveness of mixing hydrochloric acid and organic acid as stimulation fluids in a tight gas carbonate reservoir

“…[13,23,29] Organic acids, unlike hydrochloric acid (HCl), react more uniformly but may not effectively dissolve minerals that contribute to formation damage; therefore, higher volumes are often required to achieve the desired stimulation results. [30,31] Buijse et al introduced an organic acid stimulation fluid model for acid spending in carbonate reservoirs, which takes into account the acid dissociation constant to distinguish between strong (HCl) and weak (organic) acids. [32] Akanni and Nasr-El-Din developed a model that takes into account slight dissociation in aqueous solution and a fractional reaction order, using a modified reaction kinetics method for acetic acid (HAc).…”