The requirement of tapping new hydrocarbon reserves has pushed the Middle East region to develop its unconventional resources. During the development, longer laterals are drilled to achieve more stages and increase well productivity. This generates more complex intervention activities, including the post-fracturing plug millout with coiled tubing (CT). This study outlines comprehensive evaluation of frac plug milling practices integrated with designing and execution of CT operations to improve overall milling efficiency for these unconventional horizontal wells. Milling optimization was obtained by tackling key enablers of higher efficiency. First, the CT string was precisely engineered to serve the well trajectory and completion size. The tapered wall thickness configuration was strategically planned to maximize stiffness at the highly deviated section while reducing weight on the long horizontal lateral. Plug selection and placement strategy were also meticulously planned to configure the best combination of composite and dissolvable plugs. Since different plug types behave differently during milling, the millout strategy was tailored specifically for each type and their actual downhole environment. The new engineered CT design, coupled with an extended reach tool (ERT), was proven effective in overcoming reach challenges across the long lateral while maintaining sufficient weight-on-bit (WOB) to mill the plugs. The ERT was also observed to enhance milling action due to the vibrations it generated. Those improvements led to faster and smoother operations, resulting in 70% reduction of operating time compared to the baseline established prior to the start of the project. The comprehensive plug placement strategy and better understanding of different plugs behavior in different environments further improved the milling efficiency, as the average milling time per plug was reduced by 80%. Additionally, the reduction in operating time improved the environmental sustainability of the project, as carbon emissions from the CT unit were reduced. The comprehensive engineering design and plug selection strategy delivers significant improvements in millout efficiency. Implementation of key enablers led to performance increase, better resource utilization, and further cost optimization. This achievement also aligns with initiatives to reduce the impact of oil and gas operations on the environment, thus contributing to the goal of achieving net-zero in carbon emission.

Innovation and advances in technology have enabled the industry to exploit lower-permeability and more-complex reservoirs around the world. Approaches such as horizontal drilling and multistage hydraulic fracturing have expanded the envelope for economic viability. However, along with enabling economic viability in new basins come new challenges. Such is the case in the Middle East and North Africa regions, where basin complexity arising from tectonics and complicated geology is creating a difficult geomechanical environment that is impacting the success of hydraulic fracturing operations in tight reservoirs and unconventional resources. The impact has been significant, including the inability to initiate hydraulic fractures, fracture placement issues, fracture connectivity limitations, casing deformation problems, and production impairment challenges. Completion quality (CQ) relates to the ability to generate the required hydraulic fracture surface area and sustained fracture conductivity that will permit hydrocarbon flow from the formation to the wellbore at economic rates. It groups parameters related to the in-situ state of stress (including ordering, orientation, and amount of anisotropy), elastic properties (e.g., Young's modulus and Poisson's ratio), pore pressure, and the presence of natural fractures and faults. Collectively, this group of properties impacts many key aspects determining the geometry of the fracture, particularly lateral extent and vertical containment. Heterogeneity in CQ often necessitates customizing well placement and completion designs based on regional or local variability. This customization is particularly important to address local heterogeneity in the stress state and horizontal features in the rock fabric (e.g., laminations, weak interfaces, and natural fractures) that have been identified as key contributors impacting the success of hydraulic fracture treatments. Given the observation that a wide range of CQ heterogeneity was creating a complex impact on hydraulic fracture performance, CQ classes were introduced to characterize the risk of developing hydraulic fracture complexity in the horizontal plane and the associated impact on well delivery and production performance. They indicate the expected hydraulic fracture geometry at a given location and are analyzed in the context of a wellbore trajectory in a given local stress state. CQ class 1 denotes locations where conditions lead to the formation of vertical hydraulic fractures, CQ class 2 denotes locations where conditions lead to the formation of a T-shaped or twist/turn in the hydraulic fracture, and CQ class 3 denotes locations where conditions lead to the formation of hydraulic fracture with predominantly horizontal components. Wellbore measurements indicate that these CQ classes can vary along the length of the wellbore, and 3D geomechanical studies indicate that they can vary spatially across a basin. By understanding this variability in CQ class, well placement and completion design strategies can be optimized to overcome reservoirheterogeneity and enable successful hydraulic fracturing in more challenging environments. This paper introduces the novel concept of CQ class to characterize basin complexity; shows examples of CQ class variability from around the world; and provides integrated drilling, completion, and stimulation strategies to mitigate the risks to hydraulic fracturing operations and optimize production performance.

No abstract

Openhole multistage (OHMS) completion systems have been available for nearly 20 years. Their introduction was primarily linked to improved operational efficiency, achievable through the elimination of redundant operations, costs, and time from the existing application of plug-and-perf (P&P) solutions. However, increased understanding with time has demonstrated that the most effective applications of the approach are those that offer better connection within the reservoir. Examples of such applications include delivery of fracturing within extended reach wells, application to naturally fractured formations, and use of the OHMS systems in offshore or logistically challenged areas. The use of an OHMS system has a number of potential advantages for certain applications, not least of which is preservation of the uncemented annulus with extensive direct reservoir access within the completion. One of the major advantages of this geometry is that there is an unparalleled and flawless wellbore-to-reservoir communication in place, immediately prior to fracturing. In hard-rock, high-stress-ratio cased-cemented scenarios, where tortuosity and near-wellbore friction can dominate, an ability to avoid such issues in the first place is an advantage. This is particularly true in those horizontal wells drilled and completed in complex stress regimes. In these cases, a complex connection resulting from perforating can often be detrimental to creation of desired fracture width, making proppant placement challenging and thereby reducing the effective fracture conductivity. Within the Khazzan field, in the Sultanate of Oman, such a complex tectonically impacted stress-state exists in the formations of interest, combined with an ancient hard-rock environment exhibiting a wide variance in effective permeability. Early multifractured cased-cemented horizontal well simmediately demonstrated complex fracture-to-wellbore communication behaviour, which was addressed in a number of ways. One of these approaches included plans for deployment of the OHMS as a potential technique to ensure a smoother and simplerfracture-to-wellbore interface. This paper will fully describe the experience of the first OHMS completion deployed in the Khazzan field including details on the fracture design, operational execution, surveillance, post-fracture cleanup, and productivity. The paper will particularly address those aspects related to near-wellbore tortuosity, fracture connectivity, proppant placement, and evidence of connection quality. The paper will assess this completion approach alongside previously applied techniques and report on the potential of the approach for more widespread deployment in resolving fracture complexity.

The Khazzan development in the Sultanate of Oman operated by BP includes a multi-layered gas reservoir with stresses impacted by tectonic activity which has led to numerous challenges around multi-stage hydraulic fracturing of horizontal wells within the field. These wells were primarily focused on cased-cemented horizontal sections through the reservoir but a decision was taken in 2014 to trial openhole multistage (OHMS) completion systems to understand their applicability in this field and the potential advantages such systems could bring with respect to the challenges seen in the cased-cemented systems. Two such systems have been run to date in the Khazzan development. Significant consideration has been given during the planning phase to follow a systematic process of implementation to deliver an effective learning curve with clear understanding of the impact of design and execution changes between wells. This paper will describe the details, including completion and fracturing design, fracturing execution and surveillance, and post-fracturing clean up and production, of the second OHMS well in the Khazzan development. The second well has built on the success of the initial trial and the well has been designed to demonstrate the repeatability and the reliability of this completion type in Khazzan. It was also tailored to further the understanding of some key unknown or uncertain elements of the fracturing treatments following the analysis and interpretation of the first OHMS completion. Specific focus areas that will be addressed in this paper include the use of a hydraulically activated toe fracturing sleeve, the effect of a reduction of mechanical packer spacing on fracture staging performance and efficiency, ball drop efficiency, and overall fracture execution efficiency improvements. A comparison of the system's performance across different reservoir quality will be examined, with the second system having been deliberately deployed in relatively low reservoir quality rock. The impact of various degrees of over-flush and under-flush on the individual fracture stage production performance will be reviewed. This is an important consideration for more conventional Middle East reservoirs and is often perceived to be a barrier to the implementation of the highly efficient systems currently deployed by North America.