The low success rate of curing complete loss of circulation across fractured carbonates in the field, where all kind of loss circulation material and unconventional plugs were tried without success, required better understating of the fractures and changes to the well design and drilling practices to ensure proper zonal isolation and well integrity. This paper describes the successful planning and implementation of these changes and how they improved overall well construction performance. As most of the total losses occurred in the intermediate section, which combines pressurized water injection formation with depleted oil-bearing reservoir, curing process was very often never achieved. Understanding that some areas of the field are naturally highly fractured, but specially characterized by carbonate karst, dissolution, and mega fractures, was critical to map the high-risk area and modify the well design and practices. The innovative risk-based well design was deployed to a series of wells across the field. The isolation between low- and high-pressured layers to prevent casing-to-casing annulus (CCA) sustained pressure[NMF1] throughout well life and, possibility of drilling ahead with no returns with one of layers already secured by previous casing were implemented. Suitable casing seat was selected in such way that critical high pressure and depleted zones were identified and isolated. Water-bearing layers in the upper section was efficiently balanced with enough mud weight and casing point set above risky zone with addition of double mechanical barrier with gas tight feature. Highly fractures formations in the lower section were drilled with significant lower mud weight at minimum overbalance, surge stresses and best possible fluid rheology. Casing running practices were adjusted to avoid inducing losses, cement slurries redesigned for optimum properties at minimum equivalent circulating density (ECD) and cementing jobs were conducted with full returns. The total loss events were significantly mitigated in the campaign, with overall 15% well performance improvement, ensuring zonal isolation, and reduction of future CCA occurrence, which can compromise the production casing integrity after fracking job, involves high remedial work costs, longer shutdown phase and possible production loss. This solution balances performance and costs can serve a technical reference for future application in the basin or other regions with loss-prone environment across large and fractured formations, and well integrity is a concern for operators and service companies.
Drilling S-shape wells across highly heterogenetic formations and at high inclination is particularly challenging due to increased risks, such as differential sticking, total losses and well control. This often leads to poor performance, stuck incidents, fishing operations and sidetrack. This paper aims to share the technological evolution and engineering approach to well planning and operations execution to deliver S-shape wells with long step out and high deviation. A thorough review of operational risks and associated non-productive time was performed in each hole size, namely 16" and 12". This combined with a crescent step-out, due to surface location limitations and production requirements, significantly impacted performance. Comprehensive geological and offset well analysis were put in place to select the best well design and trajectory with focus on risk reduction and outperformance. The main contributing factors to achieve that were divided into different categories: bottom hole assembly (BHA) design and latest directional drilling technology; drilling fluid selection and bridging strategy; casing running considerations; and cementing design. Following the new engineering approach and technology deployment, over 30 S-shape wells have been delivered with various step-out lengths (maximum of 3,500 ft) and tangent inclinations (maximum of 32°). Flowless operations, record wells and longest step-out S-shape were delivered throughout project life. Trajectory planning, optimized light BHA, combined with autonomous directional drilling technology and dynamic survey-while-drilling service were crucial to minimize plan complexity, stuck pipe risk whilst meeting the desired targets. Fit-for-purpose drilling fluid design and bridging strategy further helped on differential sticking and downhole mud losses prevention. For the casing to reach the bottom, it was also essential to have low friction factors through centralization stand-off optimization, lubricity enhancement and customized running schedule. Light cement slurry design and cementing job remote monitoring minimized equivalent circulating density (ECD) while ensuring solid cement bond and well integrity with real-time top of cement identification. The gradual evolution of engineering and technology deployment based on well-customized risk assessment led to drilling the most challenging S-shape wells and record-breaking performance in the gas field in the Middle East. This strategy will serve as a reference for service companies and operators to accelerate learning curve and achieve similar step change operations.
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