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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.
Abstract This paper will cover the design and installation of BP’s first 15Kpsi Open Hole (OH) completion in the Sultanate of Oman in March 2016 and also the initial execution results of the stimulation treatments in July/August of the same year. This change to the current well design and execution strategy has become necessary due to variable cased hole horizontal well results and greater understanding of the challenges of delivering efficient and sustained gas production from the higher fracture gradient areas of the Barik reservoir. The Khazzan (Barik) development in the Sultanate of Oman operated by BP is a tight gas project, requiring hydraulic fracturing of tight gas resources. Tight gas production from the deep hot reservoirs in the Sultanate of Oman has historically concentrated on cased hole completions stimulated with large hydraulic fractures. The original Basis of Design for Khazzan for Full Field Development consisted of horizontal wells with multiple hydraulic fracturing stages performed within a Cased & Perforated 4-1/2″ liner design. Challenges encountered with the CH approach have included the following: Tight pressure deployment/pumping window within the existing completion design, complicated by a wide variation in areal and vertical stress regime. Variability in the injection response, proppant placement and particularly the quality of the fracture/wellbore connection that would and has been achieved. Lack of predictability regarding post-frac production rate, due to a variation in fracture placement achieved due to above two reasons. In 2014 a decision was made to introduce some flexibility in evaluating suitable fracturing designs incorporating a number of Lower Completion (LC) styles, one of which was a horizontal open-hole completion. Optimizing stimulation performance by evaluating ball dropped activated systems and over-displacement was seen to have significant potential. A multi-disciplinary approach involving drilling, completion, stimulation, intervention and subsurface was performed to ensure Project value was maximized and the objectives delivered. This paper will cover how the pressure rating of the OH completion was designed to 15 kpsi, in excess of the existing CH pressure rating. This includes screening and evaluation of the available open-hole LC system design and operational characteristics suitable to deliver propped gel fractures in 6″ OH for 1,000 m horizontal wells. Screening criteria included; system/equipment technology status, associated drilling requirements and design for "5-7/8″ hole" cost and duration versus the existing 8-3/8″ hole configuration and an ability to meet the well stimulation Statement of Requirements (e.g. fracture placement, zonal isolation). The final system design will be detailed including wellbore orientation and trajectory, hole and casing sizes, zonal access and isolation method(s) and hydraulic fracture parameters, including fracture spacing, geometry and treatment design. Operational results will be presented for well construction and stimulation phases. Well construction results will include drilling performance comparison, wellbore preparation for the completion installation, drill-in/completion fluid requirements and packer spacing/zone selection criteria. Stimulation execution results will include evaluation of execution versus design, comparison of stimulation results for ball drop stage results versus plug and perf results. Assessment of Radioactive (RA) tracer results and evidence for OH packer integrity will also be presented. Conclusions will include an initial comparison of the execution of the drilling, completion and stimulation phases and lessons learned on the success of the design versus the original objectives.
Abstract One often overlooked aspect of hydraulic fracturing is that the majority of reasonable permeability reservoirs (0.1 mD and above), on the North American continent, were in fact originally completed with straightforward hydraulically fractured vertical wells. However, as the average permeability of formations being developed deteriorated, this triggered a transition to multi-stage fractured horizontal wells and not unreasonably the fracture design and techniques that were developed to move from stage to stage were designed to be fit for purpose in these much lower permeability environments. These approaches, while suitable for lower permeability and unconventional formations, are not necessarily appropriate for higher permeabilities and conventional reservoirs. The Khazzan development in the Sultanate of Oman Block 61 includes a multi-layered, reasonable permeability, gas reservoir, which may be categorized as a tight gas reservoir. In such tight gas developments, fractured vertical wells have historically been the preferred completion design, due to favourable economics. Following an extensive appraisal programme, the development of the Barik reservoir in Block 61 was approved in February 2014, and while successful appraisal had taken place with fractured vertical wells, not unexpectedly multi-stage fractured horizontal wells were subsequently proposed as an additional incremental improvement option for development. In order to successfully achieve this, a number of standard operational practices and assumptions associated with North American unconventional horizontals needed to be challenged, adapted and in some cases stopped. The technical journey to deliver an effective multistage well design included an assessment of the impact of assumptions and considerations that drive unconventional practice, eventually leading to the road map to success that was developed. The learning includes three key pilot horizontal wells and clearly demonstrates incremental progression that was achieved, including technical obstacles faced, engagement with a complex stress-regime and how unconventional technology has to be adapted to be fit for purpose for the formation at hand. Not a static solution, the Khazzan development continues in the initial phase with fractured vertical wells achieving a rapid learning-curve and multi-stage fractured horizontal wells being optimized further. The experiences and outcomes from the suite of wells in this project demonstrated that multistage fracturing of horizontal wells requires careful consideration, particularly in the selection of technologies and their application. The approach adopted in this project has led to developing the field with a healthy suite of competing completion techniques that offer best-fit solutions under different scenarios, and this set of complementary options will ensure that the development economics are maximised.
Al-Thuwaini, J.. (Lukoil Saudi Arabia Energy Limited) | Emad, M.. (Lukoil Saudi Arabia Energy Limited) | Ekpe, J.. (Lukoil Saudi Arabia Energy Limited) | Jaffery, M.. (Schlumberger) | Ong, D.. (Schlumberger) | Taoutaou, S.. (Schlumberger) | Ahmad, B.. (Schlumberger)
Abstract Zonal isolation has extreme significance in the construction quality and life of a well. Achieving zonal isolation in deep high- pressure, high-temperature (HPHT) gas wells is a challenging task, and these wells need more attention to achieve zonal isolation than conventional oil or gas wells. In addition to following primary industry best practices, the selection of a cement system appropriate for the environment of the well is very significant. Trapped gas and oil between production and intermediate casing (abnormal annulus wellhead pressure) has been globally recognized as one of the serious challenges facing drilling and production operations. The issue is becoming even more serious since wells are aging and the integrity of the casing portion below the well head is increasingly affected by the shallow-water corrosive environment. The potential safety and environmental hazards of the abnormal annulus pressure, have encouraged LUKSAR (Lukoil Saudi Arabia Energy Limited) to review the current drilling and cementing practices, with the goal of minimizing the impact of the problem, thus improving well life cycle and reducing the frequent work-over interventions. The general guidelines set to resolve the problem focused on eliminating potential leakage paths in the completion and casing strings and emphasized the quality of the primary cementing, especially for casings set on the aquifer zones and production casings. This paper discusses case histories and selection criteria for the different cement systems. It shows how high-performance lightweight sealant across weak zones, fiber-based sealant technology when lost circulation prevails, self healing sealant system where zonal isolation is extremely important, and flexible and expanding sealant for frac candidates are chosen for providing and maintaining well integrity in these extremely remote and challenging HPHT wells.
Bugrayev, Amanmammet (Schlumberger) | Nafikova, Svetlana (Schlumberger) | Taoutaou, Salim (Schlumberger) | Timonin, Andrey (Schlumberger) | Gurbanov, Guvanch (Schlumberger) | Rovshenov, Gadam (Schlumberger) | El Sayed, Mohamed (Dragon Oil) | Hay, Kevin (Dragon Oil)
Abstract Complete and durable zonal isolation is the foremost goal of the cement job. In the deep and high-pressure environment, obtaining such goal is particularly critical, but also challenging due to the additional factors associated with the high drilling fluid densities that limit mud removal efficiency, narrow margins between fracture and pore pressures that cause loss circulation and differential sticking, and cement sheath exposure to downhole stresses during construction and production phases that compromises its integrity. Careful planning is required to ensure all risks are captured and mitigated during the design stage, taking into consideration not only the construction phase, but also post-placement downhole conditions changes caused by temperature, pressure fluctuations, and mechanical shocks during perforation and stimulation operations. Data analysis of the offset wells located in the eastern section of the Caspian shelf showed that conventional cement systems and previously applied cement job designs had limited success in addressing those challenging complex requirements. Thus, a new approach was required. This approach was used in 20 wells in the field with excellent results. Two wells were used to demonstrate the improvements obtained in zonal isolation behind production liners upon implementation of new engineered methodology. The innovative complex approach involved not only the revision of the previously used cement and spacer fluid designs, but also required revisiting and evaluating every aspect of cementing practices to achieve the desired results. Fiber-based spacer technology was introduced to enhance mud displacement and an engineered flexible and expanding cement system to achieve and maintain well integrity. Numerical analysis modelling was used to simulate the stresses that the cement sheath will experience over the well's life and calculate the minimum required mechanical properties of cement to be able to withstand these stresses. The set cement mechanical properties were then customized using a proprietary trimodal particle-size distribution technology to accommodate the expected downhole stresses. Hydraulic isolation improvement was achieved and confirmed by downhole logs.