Chevron Iraq Limited carried out a drill-stem test (DST) campaign in the Kurdistan Region of Iraq starting in year 2014. Several reservoirs with varying characteristics were targeted.

The designs of the executed stimulation treatments were based on reservoir and fluid information acquired during the drilling phase. The complex carbonate formations presented uncertainties in terms of the formation fluids, lithology, and the type and severity of formation damage that may have been present. This was a challenge toward stimulation fluids design and treatment placement. With the objective of optimizing stimulation treatments in the tested intervals, stimulation design best practices were applied and a three different stimulation methods were utilized including a hybrid matrix acidizing / acid fracturing approach.

In order to design the treatments, open hole logs, drilling fluids damage from mud losses, fluids compatibility, fracture pressures, placement rates, and other well conditions were considered. The bottom-hole pressure recording and the production results measured through the DST operations enabled an in-depth evaluation of the acid response as the campaign progressed and provided valuable data for optimization of the stimulation strategy from one treatment to the next.

This paper explains the stimulation fluids selection, quality assurance, fluids placement design, the three differing stimulation strategies applied and rationale for applying them, operational execution, and evaluation of the results in addition to the lessons learned for the way forward. This will be of interest and may be beneficial to those with similar projects involving complex carbonate reservoirs in northern Iraq and other areas of the world.

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