رسائل دكتوراة
English
2023
Sustaining Hydraulic Conductivity in Soft/Acid Damaged Carbonate Fractures: Chemical Treatment for Enhanced Performance
Abdul Jamiu Amao, Murtada Al-Jawad , محمود حسن محمد دسوقي
كلية هندسة البترول وعلوم الأرض-جامعة الملك فهد للبترول والمعادن · السعودية
The successful implementation of hydraulic/acid fracture operations in carbonate formations heavily relies on the mechanical properties of the rock post-treatment. Preserving the integrity of the rock is crucial for maintaining conductivity in the created fractures under stress. However, weak formations or excessive acid etching can lead to significant declines in productivity due to rock failure and creep. To address this issue, strengthening chemicals are being explored to enhance rock strength and sustain high stresses, thereby preserving fracture conductivity. Previous studies have demonstrated the ability to alter the mechanical properties of carbonate rocks using strengthening chemicals such as diammonium phosphate (DAP). In the context of acid fracturing, adopting the concept of rock strengthening is vital for sustaining fracture conductivity, which is directly influenced by the stiffness of the rock.Therefore, a systematic experimental methodology was developed to investigate the efficacy of the DAP-strengthening chemical in altering the mechanical properties of carbonate rocks for acid fracturing applications. The stiffness of the rock samples was measured using the non-destructive impulse hammering technique, while acid etching and hydraulic/acid fracture conductivity were evaluated using the API conductivity cell. Various analytical techniques, including Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), and energy dispersive microscopy (EDS), were employed to analyze the treated samples and gain insights into the accompanying changes. Statistical analyses were performed to assess the significance of the strengthening effect, and the parameters of pressure, temperature, and time were systematically varied to understand their influence on the overall outcomes.The results revealed that 1M DAP solution has the potential to significantly enhance the stiffness of the soft and acid-damaged samples by the formation of hydroxyapatite (HAP). As a result, the hydraulic conductivity in both DAP-stiffened intact and DAP-stiffened acidized fractures showed significant improvement, with at least a twofold increase in the short-term and long-term performance in Indiana limestone and even up to eightfold enhancement in Austin Chalk. Furthermore, temperature was identified as the most critical parameter influencing the DAP reaction with calcite in the tested carbonate samples, making it a practical solution for reservoir conditions. These findings promise to address a common challenge in the petroleum industry and mitigate its impact.