Raageshwari gas field is located in RJ-ON 90/1 Block in western India with Cairn Oil & Gas, a vertical of Vedanta Limited as operator of the field. Multistage hydraulic fracturing is required to achieve commercial production from the highly laminated retrograde gas condensate reservoir. It has been observed in almost all wells that the top high PI zones produce a majority of the gas. The wells have a water column across bottom few fracs which prohibits production from these zones. Water unloading through increased drawdown was not successful because of higher PI of the upper fracs. Coiled tubing-based nitrogen lift of the water column is not commercially feasible. It is important to find a low-cost solution for water unloading since bottom zones account for approximately 30% of total gas in place. A solution has been developed using a customized velocity string design, which can unload the water while maintaining high well production. Conventional velocity strings are only installed in late life of gas wells when liquid loading is observed. These conventional designs limit the maximum rate to 2-3 MMSCFD and therefore cannot be used in Raageshwari gas field for water unloading as high individual well rates (8 to 12 MMSCFD) is required to meet field plateau production. After reviewing various options, an innovative and unique velocity string system design was developed which incorporates a customized surface spool and string hanging system. This customized design allows combined or independent gas flow conduits as described below: Through the annulus of velocity string and tubing when higher gas rates are required. Through the velocity string to facilitate liquid unloading due to high gas velocity. Production from both the conduits to meet higher demands than the annulus flow alone. Well integrity was assured by maintaining two independent barriers during commissioning, production phase and also during future string retrieval. This paper will discuss in detail the design considerations of the velocity string and surface hanger system to achieve liquid unloading while maintaining high rate gas production. It will also have details on the dual barrier selection process and the design customization that have been done to ensure cyclic liquid unloading and high rate gas production. This innovative velocity string design is technically a dual completion with a much lower cost and footprint. The same design can be implemented across a wide variety of applications to address well integrity issues, selective zonal production etc. The application of this design in Raageshwari field will ensure planned recovery of gas from the field and will also support plateau production phase. This design can be an efficient and economic technique to develop similar fields.
Objectives/Scope Raageshwari Deep Gas field located in southern Barmer Basin, in the state of Rajasthan (India), consists of a laminated reservoir where conventional fracturing treatments with a single set of perforations are not economical. In order to improve the project economics, limited entry treatment design (Lagrone, 1963) selected for fracturing. The effectiveness of fluid diversion during limited entry fracture treatment in a laminated reservoir was validated using post injection temperature surveys. Methods, Procedures, Process The Limited entry design relies on the pressure drop across the perforations to balance the flow between the various perforation clusters. The treatment design was based on achieving a minimum of 700 psi of perforation friction for adequate diversion between the zones. The perforation friction and number of active perforations was determined using Step Rate/Step Down Tests (SRT/SDT). Post injection temperature surveys were used to confirm fluid entry into the various perforation clusters. Results, Observations, Conclusions The following process was applied to more than 90 fracture stages in 15 wells. The fracturing treatments were modeled using log derived mechanical properties and stress contrasts. Diversion into all the clusters was insured by distributing the available perforations based on the predicted fracturing pressure for each zone. Post injection temperature surveys were used to validate the fracturing models. While somewhat qualitative, the post injection surveys did provide valuable insite in some cases, the fracturing simulator predicted fracture growth out of the desired stage area. The post injection temperature survey helped to validate predictions of: In some cases, post SRT temperature surveys helped justify decisions addition of holes to minimize perforation friction or addition of extra cluster(s) to maximize pay coverage. Novel/Additive Information While the use of temperature surveys to estimate fracture height is not new, we believe that this is the most extensive use of temperature surveys in a medium size project incorporating limited entry.
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