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Experimental Investigation of Foam-Acid Injection in Carbonate Formation

Ghanavati, Amir Mohammad | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58764 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Mohammad, Bazargan
  7. Abstract:
  8. Carbonate matrix acidizing is a widely applied stimulation technique for enhancing oil and gas wells productivity through the formation of highly conductive channels known as wormholes. Uniform acid distribution within the target formations is a key factor governing the success of this stimulation method. However, in carbonate reservoirs, strong heterogeneity among productive layers and the presence of preferential flow paths such as fractures and wormholes hinder effective stimulation of less permeable intervals, thereby reducing acidizing efficiency. To address this challenge, diversion methods are employed during acidizing operations to temporarily block highly permeable pathways and redirect the acid toward other production intervals. In this study, the plugging performance of foam as a diverting fluid within wormholes was evaluated. By identifying the key parameters affecting foam stability and plugging strength, the potential for improving foam diversion efficiency in carbonate acidizing was investigated. To achieve this objective, a series of laboratory experiments were conducted, including bulk foam stability tests, acid flooding of carbonate core samples, and foam flooding of cores containing dissolution structures. Screening of foam properties for two amphoteric and anionic foaming agents revealed that increasing CaCl₂ salinity up to 5wt% reduced the half-life of amphoteric foam from 461 minutes in distilled water to 76 minutes. Nevertheless, under various CaCl₂ concentrations, amphoteric foam exhibited superior texture, foamability, and stability compared to anionic foam. Furthermore, amphoteric foam demonstrated a half-life exceeding 9 hours in the presence of 15wt% HCl, and an improvement in stability was observed with increasing acid concentration while maintaining foamability. In contrast, anionic foam was highly sensitive to acid, exhibiting a half-life of less than 2 minutes and failing to form a stable foam in contact with 15wt% HCl. Acid flooding experiments using 1wt% HCl identified injection rate as a critical parameter governing the wormholing process. At an injection rate of 4 cm³/min, a dominant wormhole penetrated the core with the minimum acid volume to breakthrough (98.7 cm³). Injection at rates higher than the optimum, such as 8 cm³/min, resulted in increased acid consumption up to 136.5 cm³, and CT scan images revealed the formation of ramified wormhole with lateral branches and dead-end wormholes advancement. Foam flooding tests conducted in both dominant and ramified wormholes demonstrated that foam quality significantly influences flow resistance and plugging strength. These characteristics were quantified using steady-state pressure drop and resistance factor (the ratio of steady-state pressure drop during foam flow to that during foaming agent solution). Within the foam quality range of 30% to 75%, increasing foam quality enhanced both parameters, whereas a declining trend was observed as foam quality increased from 75% to 95%. At a foam quality of 75%, maximum plugging performance was achieved, with a steady-state pressure drop of 4.7 psi and a resistance factor of 5.22 in the dominant wormhole. Additionally, foam propagation in ramified wormhole led to further increases in steady-state pressure drop and resistance factor, reaching 6.4 psi and 5.82, respectively. Based on these findings, foam injection at a quality of 75% is recommended for temporary wormhole plugging and enhanced diversion performance in carbonate matrix acidizing
  9. Keywords:
  10. Wormhole ; Foam Stability ; Core Flooding ; Carbonate Acidizing ; Foam Diversion ; Foam Plugging Strength

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