Abstract

High reservoir heterogeneity and tightness necessitate the application of new stimulation technology targeting good fracture conductivity and deep penetration for effective productivity and recovery enhancement. With efforts of multidisciplinary team, new Acid Fracture fluid, diverter and high leak off control technologies have been designed and executed successfully as first time ever covering multiple layers in Mauddud carbonate reservoir in Bahra field.

Mauddud is heterogeneous, tight multilayer limestone reservoir especially in Bahra field which is still under exploration phase despite having initial production early 1975. Owing to the low reservoir transmissibility, production performance has historically been poor, even with Artificial Lift and conventional Stimulation. Therefore, full-scale commercial exploitation of the Mauddud/Bahra reservoir requires advanced technologies for productivity enhancement.

One of the oldest Mauddud vertical wells in Bahra field was drilled in 1974, completed across all Mauddud layers. It was initially produced naturally at very low rate and intermittent flow periods till ceased to flow in 2001. ESP was installed in 2007, and conventional Matrix Acid stimulation was performed with very steep post-treatment decline rate. It was produced intermittently for 4 months, and then closed in due to too low reservoir inflow. This well was selected for first application of Acid-Fracturing due to its relatively good reservoir development with high (~virgin) pressure, but low production rates.

The job was designed to implement one-stage Acid Fracturing using new acid fluid diverter technology to enable covering all perforated Mauddud layers, and maximizing fracture conductivity and penetration. Many technical and operational challenges were faced and properly handled through integrated communication between different concerned teams with lessons learned are to be considered in next designs and executions.

Post-Acid-Fracturing Production results showed initial high rate at high bottom-hole flowing pressure, followed by a gradual decline in rate and pressure representing transient flow period until reached reasonable stabilization. The nodal analysis has estimated post stimulation reservoir productivity improvement by ~3 folds based on the average stabilized rate and pressure.

The positive results of this first Acid Fracturing has set up the foundation for productivity enhancement and Mauddud reservoir development strategy for existing and new planned wells in Bahra field. As a prompt action, 2 more wells (1 existing and 1 new) have been acid fractured with good results.

It is expected that the oil gain potential will be significantly more in Horizontal Completions due to more extended reservoir coverage. Therefore, Acid Fracturing Stimulation for horizontal wells is under study for Bahra Mauddud Reservoir. The success of such application will formulate the drilling, completion and stimulation development strategy for the entire Mauddud Reservoir including early stimulation to improve initial productivity that will contribute significantly to the North Kuwait production target.

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