Abstract
Acid fracturing is a widely accepted technique to enhance production for carbonate reservoirs. This has been considered suitable for Tengiz Unit 2 reservoir development, which is characterized by tight matrix quality and low level of natural fracturing. Given the recent initiation of multi-stage acid fracturing in the development of Unit 2 (U2), it is essential to quickly integrate the most effective operational strategies and the latest data on reservoir characterization into the planning of upcoming operations.
The methodology involved formulating the stimulation plan by integrating open hole logging data from Unit 2 intervals, considering relatively higher water-cut production from new wells, and utilizing acid fracturing simulations informed by existing geomechanical rock properties. This approach aimed to determine the ideal treatment sizes and flow rates for the job designs. The use of conformance control liners (CCL) in the lower completion, coupled with the EverGreen Burner (Management of Residual Materials, MRM, suite) for the initial well cleanup, enables the independent testing of Unit 2 to evaluate the success of the acid fracturing operations completing the full cycle of acid frac execution and assessment.
Every new acid frac job has been based on the experience of the preceding jobs allowing for several areas for improvement. Acid recipe and volumes were the most frequent subjects to change that tested utilization of retarded acid, diverter acid system, pad gel and hydrochloric acid. On the other hand, the different intervals of Unit 2 were targeted for stimulation implying the varying nature of reservoir properties, the water risk and frac gradients in particular. Thus, the wells and reservoir compartments of interest showed contrasting productivity and water-cut that also has been a significant driver to manage the intensity of treatment by injection rate and acid volumes. The staged stimulation approach leveraged the benefits of CCL completion in the tight formation which accommodated selective treatment and delivered proper isolation between the stages. Some on-fly adjustments based on the set of calibration tests are also going to be shared along with the enhancement suggestions for execution process.
The aggregate of rigless equipment, MRM well clean-up spread, slickline/wireline tools, permanent downhole gauges, and CCL well completion provide great flexibility and efficiency in planning and execution of acid fracturing in the described conditions of the tight almost undepleted carbonate reservoir. Analysis of treatment charts might shed light on the effectiveness of treatment fluid systems in terms of anticipated pressure behavior. The well flowing data and further surveillance also backs up the assessment of the acid frac reducing the uncertainties for water and productivity.
