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An operator developing a deepwater field in the eastern Mediterranean required to monitor pressures in an upper sand section while producing from the main lower sands. If communication existed between the two zones, a planned late-life workover could be eliminated, reducing development cost. Gauges placed across the upper sands in a pilot hole would transmit pressure data to the production bore using electromagnetic (EM) transmission technology. Ensuring isolation of these gauges by cement was identified as critical in enabling effective EM data transmission and therefore a great deal of focus was placed on the design of the cement job. To perform the operation in as efficient manner as possible a tailored assembly was developed consisting of electronic gauges and EM relays isolated by open hole packers, along with a cementing assembly to allow cementation of the upper part of the string which included an EM receiver and relay in place. The cementing assembly consisted of a frac sleeve to allow the completion to be run and cemented in place, and a disconnect tool for the drill string to be disconnected in one run. Once disconnected from the completion, the abandonment of the pilot hole could continue without a trip out of the hole, saving significant time and costs to the operator. The cementjob design was tailored and verified by lab testing and software modelling to meet the objectives of the job and the unique challenge associated with the placement method proposed. Once the completion was installed in the production bore, communication between the gauges through the EM transmission system was confirmed and monitored during the subsequent well cleanup. The communication test verified annular isolation and system operability. Furthermore, upper and lower zonal isolation was proven by monitoring the gauge data in an interference test when flowing another well.
An operator developing a deepwater field in the eastern Mediterranean required to monitor pressures in an upper sand section while producing from the main lower sands. If communication existed between the two zones, a planned late-life workover could be eliminated, reducing development cost. Gauges placed across the upper sands in a pilot hole would transmit pressure data to the production bore using electromagnetic (EM) transmission technology. Ensuring isolation of these gauges by cement was identified as critical in enabling effective EM data transmission and therefore a great deal of focus was placed on the design of the cement job. To perform the operation in as efficient manner as possible a tailored assembly was developed consisting of electronic gauges and EM relays isolated by open hole packers, along with a cementing assembly to allow cementation of the upper part of the string which included an EM receiver and relay in place. The cementing assembly consisted of a frac sleeve to allow the completion to be run and cemented in place, and a disconnect tool for the drill string to be disconnected in one run. Once disconnected from the completion, the abandonment of the pilot hole could continue without a trip out of the hole, saving significant time and costs to the operator. The cementjob design was tailored and verified by lab testing and software modelling to meet the objectives of the job and the unique challenge associated with the placement method proposed. Once the completion was installed in the production bore, communication between the gauges through the EM transmission system was confirmed and monitored during the subsequent well cleanup. The communication test verified annular isolation and system operability. Furthermore, upper and lower zonal isolation was proven by monitoring the gauge data in an interference test when flowing another well.
Typically, most of the well abandonment practice is reference to the recognized industry standards i.e. NORSOK, UK Oil & Gas and etc, and this is how the wells abandonment was carried out in the past. These practices however evolved/changed over time with lessons learnt and experiences and turn into a fit for purpose solutions for the Client. The shift in international and local standards and regulations for a robust plug and abandonment approach has placed the need for a better and long lasting permanent P&A methodology. Adhering to the existing industry standards in well abandonment is somehow not practical and not cost effective to be implemented in different part of the well, where there are major differences in local regulations, reservoir conditions, caprock thickness, well design philosophy and etc. The magnitude of abandonment cost increase is not at par with the risk reduction in long term hydrocarbon leakage. A fit for purpose solutions is recommended in closing the gap between cost and risk. Due to the extremely varied well architecture between wells, the approach to permanent abandonment varies depending on casing sizes, presence of packers and no of casings present to the caprock area. On top of that, identifying the highest depth for a placement of cement plug will reduce on the amount of plugs to be placed, saving rig time and operational time. So far, 16 idle wells have since been permanently abandoned with the systematic approach of applying caprock restoration concept and reinstating the poor isolation across caprock areas with cement with the assistance of technology to the likes of perf-wash-cement, and hydro mechanical casing cutter. These wells have successfully been abandoned as per host authority standards. This paper will explore a major local oil company’ approach to decommissioning of wells, in line with local regulations enforced, while ensuring a cost effective approach is applied in line with the available technologies.
End-of-well operations can improve drilling performance through selection of the proper tools to optimize rig time and tailoring solutions. For deepwater projects, it is necessary to optimize costs without compromising safety and quality while delivering maximum efficiency. An innovative technique is presented for placing a long cementing plug using sacrificial tubing and a special tool. This method also allowed checking the top of cement (TOC) after a short waiting on cement (WOC) period. Plugging and abandonment operations were performed in deepwater wells in the Caribbean Sea, saving up to two days of rig time by using a single intervention to isolate the openhole length from 600 to 1500 m and allowing continued, timely operations. A case study of this operation is presented that discusses the experience and lessons acquired, which should be beneficial for the industry. Conventional balanced plugs are not efficient in openhole lengths greater than 500 ft because of operational limitations and design considerations. In such scenarios, fit-for-purpose downhole tools can provide reliable solutions, such as using a release mechanism to safely place a cement plug of the necessary length with proper thickening time distributed along the volume pumped. This technique avoids the long WOC times necessary to achieve adequate compressive strength. The release tool enables running sacrificial pipe; placing cement through the sacrificial pipe; displacing cement slurry with a dart, which provides an indication of its latching at the surface; and disconnecting to retrieve the landing string. In the laboratory, a 500-psi slurry compressive strength was obtained after 6 hours and 15 minutes. This allowed the TOC to be tagged after 6 hours of WOC. Because this procedure does not require the 3 1/2-in. stinger to be pulled out of the plug, the risk of spacer contamination in the slurry was reduced. Based on laboratory results, three operations using the release tool and discussed design considerations were performed successfully for the first time in the Caribbean Sea, with no nonproductive time (NPT) or quality issues experienced, saving up to USD 500,000 for the operator. Laboratory tests, such as compressive strength, provided a good indication of the time necessary to tag the TOC, which met the operation objectives. The tool capabilities and operational and design considerations can be used as a reference for projects in similar environments that require alternatives with proven solutions. The main benefit was reduced operator costs for rig daily charges resulting from placing one plug rather than several balanced plugs. This was also beneficial for the mud company because a large spacer volume was not incorporated into the mud. Another benefit was allowing tagging of the plug in the same operation because of the short WOC.
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