This paper presents an analysis of the stimulation treatment design and the optimization of the stimulation treatments in the challenging ultra-HPHT environment (400°F and 15000psi) of the Krishna-Godavari (KG) basin, East Coast, India. In greater detail, the paper focuses on how the perforation placement and the stimulation treatment design have been optimized for each zone of a multi-zone treatment program in a deviated well to address the specific challenges (geological, completion, operational and logistical) associated with the environment.
An in-depth analysis was performed on the stimulation design prior to mobilization of stimulation equipment and crew. The treatments were designed by utilizing as inputs tailored petrophysical and geomechanical models, well design data, stimulation material properties and equipment capacities, and analysis of prior stimulation experience in this area. Extensive sensitivity analysis was carried out to come up with the optimum perforation depths and stimulation treatment. Subsequently, when on location, the treatment design was fine-tuned using real-time data to optimally place the fracture. The overall goal was to determine the best stimulation treatment for the offshore well without inducing negatively impacting either the reservoir production or ultimate recovery. From adherence to fundamentals of well and frac design to completion optimization, major efforts were made in the treatment optimization for each zone based on the challenges associated with the KG basin. These challenges, in no particular order, include high temperature and high pressure, proximity to water zones and the necessity to isolate treatment stages using unconventional methods, presence of high fluid loss zones, and logistical/space constraints inherent from the offshore location.
Stimulation treatments implemented in this field in the past were analyzed to better understand the pros and cons of the various stimulation techniques and practices that were employed. A key learning from this exercise was that the stimulation fluid selection is of utmost importance. With a BHST of 400°F, stimulation fluids that can provide adequate stability under these conditions are limited. This led to an increased focus on the engineering design of stimulation treatments in the pre-planning phase, which was then optimized as real-time data was acquired. Wellbore re-entry issues led to further re-evaluation and redesign of the perforation strategy. Improvements in treatment sizing were made during the stimulation as water zones needed to be avoided or stress conditions needed to be corrected from early design conditions assumed. Furthermore, upon completion of each stimulation stage, proper and unconventional isolation methods were needed from earlier stimulation due to tubular limitations. Post-frac evaluation using hydraulic fracture pressure match indicated that 3 out of the 5 zones were stimulated with highly conductive and long fractures, while minimal size treatments were placed in 2 troublesome zones. Also, treating a high-risk water zone was avoided. In conclusion, the authors believe that the stimulation program was optimally designed and conducted in an area with limited success in years past by using sound engineering in all the phases of the design and implementation.
