Reinvigorating Production from High-Pressure Carbonate Reservoirs: An Innovative Stimulation Technique Combining Single Phase Retarded Inorganic Acid System with Coiled Tubing Intervention in South-East Kuwait
Authors: AlShammari B , Slama M , Badrawy K , Rane N , Al-Adwani M , AlOtaibi L , Al-Mousharji M , Al-Mehanna H , Sunagatov R , Fajardo S 
Published: February 2024

Carbonate stimulations typically require formation-dissolving chemicals to eliminate near-wellbore damage by dissolving rock matrix or generating conductive channels such as wormholes to improve connectivity between the wellbore and the reservoir. Hydrochloric acid (HCl) has been a common choice for this purpose. However, commercially available emulsified acids, which contain acid droplets within a hydrocarbon phase, are preferred for acidifying carbonate at high temperatures. Nevertheless, these emulsified acids are usually highly viscous, leading to high friction pressure that cannot be mitigated by conventional friction reducers. In contrast, a more efficient single-phase retarded inorganic acid system (SPRIAS) was introduced to overcome these limitations. This paper presents a successful case study of SPRIAS's application in the oil and gas industry, particularly in high-temperature carbonate reservoirs.

Advanced simulation software was used to model longer, intricate wormholes in high-temperature carbonate reservoirs. Selecting appropriate fluid solutions was crucial to optimize the stimulation treatment results. After laboratory testing, SPRIAS fluid was proposed to enhance the fluid selection. This addition to the selected treatment fluids improved the dissolution profile in the producing zone while reducing the reaction in the formation face. The successful application of SPRIAS resulted in a significant improvement in production rates and a longer productive life for the reservoir. This study demonstrates the effectiveness of SPRIAS in optimizing stimulation treatments for high-temperature carbonate reservoirs.

This study examines two underperforming oil wells, A and B, in South-East Kuwait, completed with 3.5-in tubing and 5.5-in liner, intersecting Middle Marrat, a tight carbonate formation with an average pressure of 9,500 psi and a bottomhole temperature of 240 DegF. The wells have a total depth of 12,700 ft and 13,400 ft, respectively, and production tubing set at 11,300 ft and 11,900 ft. SPRIAS system and viscoelastic diversion system were used to enhance the stimulation treatment results in high-temperature carbonate reservoirs. The execution began with drifting the well to target depth with a 1.75-in coiled tubing (CT), followed by injecting an aromatic solvent mixture across the liner to dissolve organic deposits. A stimulation treatment was performed, including a pre-flush, spearhead acid, and stages of SPRIAS paired with diversion. The post-stimulation production results for both wells showed a 4-to-5-fold increase in oil production. The selected fluids exhibited better solubility and controlled reaction rates, which optimized the treatment volume and increased the profitability of the stimulation treatments.

This paper presents a novel approach to reviving a well's production while maintaining optimal economic values for high-pressure carbonate formations. The success of the proposed stimulation approach delivered breakthrough results and generated new interest in the particular formation. The study increases understanding of the benefits of using SPRIAS in similar environments and serves as a valuable resource for practicing engineers in the oil and gas industry.