This paper details the planning, design and execution of a successful campaign to perforate five HPHT wells, using Coiled Tubing (CT), in the UK Central North Sea. The project goal was to perforate extended intervals, in live well conditions, in one run and leaving no guns or restrictions downhole. The well conditions presented challenges to the design and operation of CT in this campaign. Challenging factors included: The use of high yield strength CT (130,000ksi grade material). Wellhead pressure up to 9,000 psi. Bottomhole pressure up to 12,500 psi. Estimated BHT 375° F. Estimated FWHT 320° F. Well depths of 21,000 ft MDRKB. Deployment of up to 1,645 ft of 2 7/8″ perforating guns. Perforating gun string retrieval to surface. No rathole to drop guns due to: Penetration of the reservoir water bearing zone, potentially leading to produced water and scaling issues in later well life. Access required across the formation for data acquisition and reperforation operations. Cost and time involved drilling hard HPHT formations. Job design was critical to the success of the operation and consideration given to learnings from similar previous operation. This included selection and analysis of CT material, size, wall thickness and managing potential CT collapse pressure following reservoir perforation. Further analysis, included calculation of CT stretch, circulation pressure, and wellbore solids removal studies. Reverse circulation through the CT was carried out. This would increase the effectiveness of fluid displacement when creating an underbalance situation prior to perforation. In order to maintain pressure barriers specific tooling was required to minimise the risk during this operation. The completion design is discussed with specific attention to the process of eliminating the requirement to deploy and recover perforating guns whilst maintaining control of the surface pressure. The ability to maintain a dual pressure barrier within the completion saved considerable time over the conventional method of recovering long gun strings with pressure at the wellhead. An important element contribution to the success of the operation was the completion of additional equipment tests completed prior to the commencement of operations. The testing demonstrated equipment was fit for purpose and established critical interfaces as well as creating synergies with the multi-vendor delivery team. The fine-tuned operational and procedural aspects of the job and led to several modifications to equipment and procedures. Further testing was completed to confirm functionality the data acquisition, allowing monitoring and recording of pressures, circulation rate and depth control. The job design, planning, qualification of equipment and the use of dedicated competent personnel lead to the successful perforation campaign of five HPHT wells without any accidents, environmental spills or lost time and within budget.
Well intervention operations in extended-reach wells with sand, proppant, or other fill or in openhole wells are becoming important especially in the Middle East, where many exiting long openhole laterals need to be stimulated to maintain existing production. New laboratory and field results with a lubricant and a 2 ⅛-in. fluid hammer tool are shown to significantly increase the coiled tubing (CT) reach in laterals with sand. These results can be extended to openhole wells, as the coefficients of friction (CoF) between CT and metal casing completely covered with sand or an openhole are similar. While theoretically increasing the CT diameter could extend the CT reach, in practice, this may not be always possible due to completion size limitations or logistical challenges with onshore road transport or offshore crane lifting/deck loading limitations. Hydraulic technologies such as fluid hammer tools and downhole tractors have extended the CT reach significantly in cased wells, but their successful application in long openhole laterals has not been reported in literature. In addition, metal-on-metal lubricants are used in cased wells with laterals longer than 10,000 ft, but their application in similarly long sand-screen-completed or long openhole laterals is much more limited due to the higher friction. In this paper, laboratory and field results with a lubricant and a new 2 ⅛-in. fluid hammer tool are presented for sand-screen-completed wells. The lubricant was initially tested in laboratory for compatibility with representative formation rock samples. Given the fact that the lubricant itself contains a clay stabilizer component, it performs better than other commercial lubricants tested in low-, medium-, and high-permeability rock samples. The fluid pumped through the CT and 2 ⅛-in. fluid hammer tool creates pressure pulses with frequency of 8 Hz by opening and closing a valve inside the tool. These pressure pulses generate axial and radial forces that act simultaneously on counteracting the friction force between the CT and the formation: the axial force increases the bottom hole assembly (BHA) tensile load; and the radial force reduces the normal contact force, and thus the friction force. Combining the effects of the lubricant and the new 2 ⅛-in. fluid hammer tool in a pre-job CT modeling software results in CoFs reduced by 50-60%, from a default value of 0.36 without any friction reduction technology to 0.15-0.18 when both the lubricant and the tool are used. Laboratory testing with the lubricant alone showed that CoF between CT and a surface completely covered by sand decreases by 40-50%, from the default value of 0.36 to 0.18-0.22, for temperatures between 20 and 98°C. These CoFs were validated against field data from a sand-screen-completed well in the North Sea. Friction reduction of this magnitude is expected to significantly extend the CT reach in long openhole laterals. In this paper, the lubricant and the new 2 ⅛-in. fluid hammer tool are briefly described and the data acquired during the laboratory testing and field operation is discussed. These results improve the current industry understanding of the CT friction in sand-filled cased wells and openhole wells and show great benefits in using the extended-reach CT technology consisting of the lubricant, the 2 ⅛-in. fluid hammer tool, and the CT modeling software for extending the CT reach in sand-filled cased and openhole laterals.
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