Raageshwari Deep Gas: Project Overview to Develop a Volcanic Gas Reservoir Punj Sidharth, Shobhit Tiwari, Raymond Joseph Tibbles, Saurabh Anand, Vishal Ranjan, Shashank Pathak, Rajat Goyal, Pranay Shankar (Cairn India Ltd), Rajarshi Das (ONGC),
[email protected] Extended Abstract: Technological advancements have always created opportunities to surpass all constraints and bend the economics of tight hydrocarbon reservoirs towards commercial development. Technical screening and commercial evaluation of any new practices or technology is critical before implementation. These advancements have huge techno-commercial impact on the project drive. Caution however has to be taken on the evaluation of the technology to avoid any complication during the execution stage. With very limited analog field data having resemblance to target reservoirs, the task requires a vigilant and strategic approach in adapting the technology in a fit to purpose case. This paper discusses about a low permeability, moderate CGR volcanic gas condensate reservoir. The average reservoir thickness is ~700m with ~200m of clastic and ~500m of volcanic rocks with highly laminated pay intervals. The average depth of the reservoir ranges from 2,500 m TVDSS to below 3,500 m TVDSS It is a low net to gross system with high porosity reservoir sections bounded by low porosity zones. Average porosity ranges from 8% in volcanic to 12% in clastic reservoir with a relatively high average connate water saturation of 50%.
Average
permeability range from ~0.01mD in the tighter volcanics to ~1mD in the clastics. Fluid system is retrograde gas condensate with excellent quality gas with ~80% methane, low CO2 and no H2S; condensate gravity is ~560 API. Hydraulic fracturing is an integral part of developing such field. This paper aims to summarize all the technical and operational learning observed while development of this challenging deep gas field. A combination of advanced advanced technologies technologies were successfully implemented implemented which lead to optimize optimize the project economics. These technologies include limited entry fracturing in volcanic reservoir which in itself is novel. To target 4 to 5 laminated intervals with single frac stage it was needed to run 4 to 5 separate conventional perforation runs which results in increased operational time and project cost. To cater this, Addressable switch firing system technology was thoroughly evaluated and then successfully implemented for the first time in India. The paper also summarizes fracturing design and its improvisation, which includes the limited entry perforation technique,
estimation of fracture height by temperature logging which resulted to target higher Kh per frac stage and increase the EUR per well. Conventional Plug and Perforation stage for each prospective pay gives full insurance to exploit that pay but required very high number of fracturing stages and eventually results in poor economics. On the contrast Limited entry technique has its inherent risk of inadequate diversion between clusters and losing out pays and reserves. This risk was evaluated and steps were engineered to reduce the same. During each stage of Fracturing, progressive perforating with diagnostics injection and temperature surveys were conducted starting from deepest perforation interval moving up in the well. The results were then validated with Post Frac pressure matching and Temperature/production surveys. The key for successful development of such project lies in the seamless interaction of multidisciplinary teams. Apart from this, enhancements and improvisations were made in various aspects of fracturing operation to increase overall reserve recovery. These improvisations include better frac fluid design using inhouse bore well water with high boron content. Rigorous laboratory tests were conducted at various temperature ranges to ensure stable fluid recipe. In addition optimum surface tension reducing agent was used which helped to increase frac fluid recovery. Critical alterations were made while milling the bridge plugs on coil tubing to significantly reduce milling time by managing large amount of gas and condensate produced, along with milling cuttings, sand, gel and water at surface, which was an issue with regards to conventional surface equipment’s and chaotic flaring of condensate in vicinity of other gas producing wells. The best
practices were followed for optimizing the job design in context to the optimum weight on bit, penetration rate, the fluid system used for milling along with the additives which facilitated the increase in frac fluid recovery and most essentially the differential pressure across the motor. The alterations helped in significantly reducing the milling time and thus the cost of associated services. Finally the paper will summarizes on the flow-back procedures followed for the multiphase flow. The well flow is analyzed in terms of pressure parameters and the phases of flow which decides choke size. The objective of sand free rate and maximum fluid recovery holds paramount importance in the flowback procedures. Detailed planning is required for optimized resource utilization and operational excellence to achieve these goals. Apart from implementation of new technologies, important role was of strategic operational planning which includes simultaneous rig up on two wells any time for Frac. The support units were thus utilized in more efficient manner to achieve a sustainable operational efficiency. The
key factors included effective technology implementation with reduction in unproductive time better through communication. Operational efficiency is imperative in order to more effectively respond to continually changing market forces in a cost-effective manner. The continuous learnings of the campaign will definitely provide an insight in developing similar nature of tight reservoirs in a cost effective manner. One of the key reasons for the successful development of this project was advanced analysis and utilization of data acquired which generated value for the project in longer run.
