First Acid Fracturing Unlocks the Production Potential of Tight Tuba Carbonate Reservoir, North Kuwait
Authors: AL-Hassan A.. , Anthony E.. , El-Aziz S. Abd , Abdel-Basset M.. , Mokhtar A.. , Sheikh B.. 
Published: October 2015

Upcoming Reservoirs in North Kuwait will play significant role for meeting NK’s strategic production target. Recent full field study of Sabryia Tuba carbonate reservoir makes it the largest Oil in-Place of the Upcoming Reservoirs in NK. Sabriyah Tuba, though discovered in the 60’s, is still relatively under exploited presently with only 13 active wells with very low total production rate compared to other reservoirs. High reservoir heterogeneity, tightness and poor fluid properties necessitate the application of new stimulation technology targeting good frac conductivity and deep penetration for effective productivity and recovery enhancement. With efforts of a multidisciplinary team, new acid frac fluid, diverter and high leak off control technologies have been designed and executed successfully in two stages covering multiple reservoir layers for the first time in Tuba.

Tuba is tight multilayer limestone reservoir. Owing to the low reservoir transmissibility, even low average well production assisted by Artificial Lift causes near-wellbore (not regional) rapid decline in pressure. Full-scale commercial exploitation of the Tuba reservoir therefore requires advanced technologies for productivity enhancement. The well under study is vertical, drilled in 2012 and completed in Upper and Lower Tuba with conventional matrix acid stimulation which had a very steep post-treatment decline rate. It was selected for first application of acid fracturing due to its excellent reservoir development in higher structure position with high initial pressure and medium oil quality, but low production rate. The job was designed to implement a 3-stage acid frac. The first stage was successfully executed. The second and third stages were combined into one stage due to the vertical communication between all 4 Upper Tuba layers during the data fracture treatment. Many technical and operational challenges were faced and properly handled through integrated communication between different participating teams with lessons learned are to be considered in next designs and executions.

Post acid Frac, a production log (PLT) was recorded and showed greater contribution from the Upper Tuba intervals. The well has been monitored closely where stabilization was observed in short time period represented in stabilized Pump Intake pressure and production rate that has been tripled post stimulation with an estimated reservoir productivity improvement of about ~3 folds from nodal analysis.

The positive result of first acid frac reinforces the action plan to proceed with such stimulation technology.

It is expected that the oil gain potential will be significantly more in horizontal completions. Therefore, acid frac stimulation for 2 Horizontal Tuba’s wells is under study. The success of such application will formulate the drilling, completion and stimulation development strategy for the entire Tuba reservoir including early stimulation to improve initial productivity that will contribute significantly to the NK production target.

This paper describes the design, implementation and production impact of an advanced fiber based acid fracturing treatment that was successfully executed across the cased-hole of a pilot vertical well that is shaping the production enhancement strategy for Sabriya’s Tuba tight reservoir in North Kuwait field. The paper also focuses on the acid fracturing technique that delivers hydraulic acid fractures with deep, infinitely conductive channel compared to conventional acid stimulation techniques previously employed and their immense impact on production.