The negative impacts of high water cut in mature fields are well known within the oil & gas industry. Water production preventive & mitigative measures are well established and documented: Wireline or coil tubing conveyed diagnostic and work-over operation(s) is one of such common preventive measures. This paper, through a series of integrated case studies will highlight the best practices for wireline conveyed logging and work-overs with one common goal, i.e. to achieve the water production to a minimum acceptable level in deviated high water cut wells. The prolific XYZ field is located in the Northern North Sea and it produces oil from Jurassic Brent Group. Oil production from the XYZ reservoir started in early 1978, with 43 producing wells and 15 water injection wells targeting the Rannoch, Etive, Ness and Tarbert sands. Oil and gas production peaked in 1982 and since then production has steadily declined for this field. The increasing water cut in the wells of this field is presenting a challenge for the operating companies. Production profiling using advanced Production Logging data, casing/tubing integrity check using Multi-Finger Caliper data and saturation monitoring using cased-hole Reservoir Saturation data was done in these wells to ascertain the water producing zones and do the subsequent well intervention, if required. A strategic diagnostic test was designed to precisely evaluate the flow profile using advance production logging tool consisting of 5 mini-spinners & 6 sets of each electrical and optical probes; Real-time data assessment and analysis was done for different flowing rate surveys to validate the findings. Additionally, casing condition was evaluated using Multi-Finger Caliper to decide Plug or Straddle setting depths. Also, new hydrocarbon bearing zones were identified based on cased-hole saturation tool results. The analysis results boosted the cumulative oil production. This study demonstrates the importance of making real time interpretation decisions at the wellsite and the benefit of developing a good working relationship between wellsite engineers and onshore technical support. The results of this work led to the unequivocal determination of major oil and water producing zones in deviated high water cut (95%+) wellbores which further helped in taking workover decisions to carry out water shut off, utilizing either plug or straddle technology. The findings of caliper data determined the appropriate plug or straddle setting depths. The results were compared and confirmed with the nearby well dynamic pressures and production data. The technical approach and processes applied to wells of XYZ field is a valuable example guide to decide water shut off zones and technique of similar plays. This study consists of three integrated case studies from a mature field where water shut-off zones and technologies were decided based on the findings of production logging and well integrity data. Also, re-perforation jobs were performed based on the cased-hole reservoir saturation data results. These strategic workover operations ultimately led to significant increase in hydrocarbon production.
Moho Nord is a deep-water exploration and development project launched off the Congolese coast in March 2013. This huge investment is the largest oil & gas project ever undertaken in the Republic of the Congo and with a capacity of 140,000 barrels of oil per day. This project, operated by TOTAL (with CHEVRON and SNPC as partners) taps deposits located in water depths of 650 to 1,200 meters and connects 28 subsea wells to two Floating Production Units (FPU), with an additional 17 wells developed from a Tension Leg Platform (TLP). The project involves numerous operations as drilling, testing and completing the wells. However, these deep-water operations are extremely cost-intensive and environmentally challenging, thereby representing a high-risk/high-reward scenario. Due to the intrinsic complexities involved in deep-water operations, it demands meticulous operational planning and dictates the use of technology/practices, which maximizes quality information while minimizing rig time; with a minimal impact on the environment. This paper discusses an ongoing success story on Subsea Riser Inspection at Moho Nord, showcasing the unique challenges encountered in the operations. Also, the lessons learnt from the post-operational studies of this campaign can be utilized to optimize the future riser inspection operations globally; to achieve a more engineered approach towards operations. On Moho Nord TLP, a drilling/production riser is a conduit that provides a temporary/permanent extension of a subsea wellhead to the surface drilling/production facility (where the surface BOP is located); but is extremely critical to preserve the operational integrity of the well. Therefore, robust design followed by routine inspection and monitoring of riser integrity is crucial for the campaign’s success. The literature of oil & gas industry doesn’t report many such cases of successful subsea inspection campaigns, thereby making this a unique campaign for the operator. The campaign involved evaluating the internal and external surfaces of 18.75 inch (0.85 inch thick) Drilling & 10.75 inch (0.45 inch thick) Production risers, for which ultrasonic measurement was utilized. This technique allows scanning the pipe with high radial (up to 1.2 inch) and vertical (0.6 inch) resolutions and the measurement resolutions of 0.002 inch are achieved for both the accurate internal radius and thickness. Minimal operational footprint, well known technology, faster logging speed & quick processing in a short turnaround time (TAT) are some of the additional benefits which have resulted in choosing the ultrasonic measurement as the optimal choice for this campaign. So far 16 ultrasonic logs have been recorded in the first 8 wells across the production risers, 7 ultrasonic logs across the drilling riser and a time-lapse analysis is being carried out to continuously monitor the internal and external condition of the drilling & production risers thereby ensuring overall operational integrity of the well. This ongoing project has shown exceptional synergy between various stakeholders in the project, which has resulted in a total of > 200 hrs. of operating time with >99% operational efficiency. This paper documents the lessons learnt, leading to best practices which could be adapted anywhere globally for planning of subsea riser inspection campaigns. Also, the strengths and limitations of the ultrasonic measurement for riser inspection is clearly highlighted.
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