Well delivery in Pre-Cambrian salt with high-pressure floaters in the South of Oman provides several challenges, including Well Control Events, losses, supercharging, salt creeping, casing collapse and a negative drilling windows if section TD is picked incorrectly. The well design does not allow for an additional casing string with redundancy to case of troublesome zones. To overcome this, PDO initiated a barefoot completion as an extra hole section instead of well abandonment. As a wells recovery plan in 2017, PDO initiated different potential options to complete Ara salt wells and one of visible alternative options was to complete wells as open hole "Barefoot" completion. A design solution developed across technical functions on the suitability of barefoot completion in the carbonate reservoirs. The method to drill and complete with 3.615" hole as "Barefoot" was then expedited through detailed design as per the well delivery process. Key factors, which were considered included inflow performance and hole stability, the review of BHA design, drilling hydraulics, fluids selection and barrier considerations for barefoot completion. The operational challenges were reviewed and optimized with each implementation to drive further value. To date three wells recovered successfully with the new barefoot completion method. The wells completed with solids free drilling mud placed across the reservoir section and a suspension plug installed in the upper completion to facilitate rig release. During well testing operations; the suspension plug is removed, the openhole section is clean-up with coil tubing to remove filter cake with Enzyme treatment and finally the carbonate reservoir stimulated with gelled acid. During production tests all wells showed excellent production results and reservoir flowing coverage confirmed by spectrum noise logs (SNL), high precision temperature (HPT) and production logs (PLT). Based on three wells results; it is concluded that openhole completion can offer a valuable completion option for well recovery & may be used for optimization for current designs. The cost of the barefoot completion delivery has reduced by 20%. The production output from the wells is higher than expected; Productivity Index of those wells is relatively much better than the nearby wells. The Newly proposed design provide continuity to develope Ara Salt wells and recovery plan to overcome challenges and avoiding well abandonments. This completion option was reviewed and accepted as base case completion for some deep fields in South of Oman, where oil is encapsulated in high-pressure carbonate floaters and there no risk of water or gas breakthrough. One more additional well was planned to be completed as openhole "Barefoot" completion and cost saving of ~15% over the total well cost was achieved. This recovery option will benefit all the upcoming future wells in the area.
In South Oman, PDO is producing from high Sour Fields (H2S 1-10%) with high reservoir pressures ranging from 50,000 to 100,000kpa for more than 20 yrs. Operating these high sour wells comes with huge challenges and risks, which can easily get escalated to very high levels in case of any integrity issues with the wells. These situations not only provide significant exposure to expensive and risky well interventions but also pose threats to production due to Simultaneous Operations (SIMOPS) issues. The authors describe case studies where team was exposed to these challenging situations due to integrity failures in two such wells. New technologies were implemented which resulted in restoring the well integrity in a very cost effective manner (cost savings worth millions) and also reduced the HSE risks on the nearby operations. As a result, production was safeguarded (3-4% of Station Capacity) by allowing drilling of new wells and oil deferment from existing wells in the nearby area was avoided.
There have been many oil and gas field discoveries in the Cambrian Ara Group intra-salt carbonate rocks in the South Oman Salt Basin. These carbonates represent self-charging petroleum system with over-pressured hydrocarbon accumulation in dolomitized rock encased in the salt. Drilling and completion wells going through salt is challenging. Salt creeping behavior results in issues of stuck pipe during drilling operations, casings deformation and collapse that have led to well suspension and abandonment. The full set of the available historical data analyzed to identify magnitude and history of the problem. The study conducted to estimate of salt creep magnitude, to assess the effect of the salt creep on cement quality, drilling and completion risks. The risk of salt creep on the drilling, completion and long-term well integrity was evaluated with multi-disciplinary integration of geological, geomechanical, petrophysical and well engineering aspects to minimize and mitigate the salt creeping risks. In addition to identify root cause for completion failure and providing recommendations to drilling practices, cementation and completion design that can improve well delivery process. Salt creep behavior presents drilling challenges associated with excessive torque, stuck pipe, casing deformation, and poor cementing job. Salt creep associated risks to drilling and well integrity should be managed and mitigated. Key study findings captured for wells designs were: Salt creep rate increases with depth, salt thickness and differential stress (function of MW)Non uniform loading decreases the collapse rating of the casing and results in casing deformationNon-uniform loading likely due to poor cementing, interface between rigid carbonate intervals and salt, and irregular open hole quality. Studied casing collapse cases could likely be attributed to several factors or combinations of factors such as salt mobility behavior, drilling with low MW, poor cement jobs and loss of internal hydrostatic support for the casing after cement job between liners lap. The improved multi-disciplinary understanding of salt creep is vital to reduce drilling and completion costs, unnecessary well abandonment and achieve good life cycle well integrity i.e. avoid extra side-track and workover cost due to integrity issues. The best practices and conclusions summarized in the study for drilling and completion design expected to benefit the exploration and development projects for the salt encased carbonate reservoirs around the globe.
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