Storage of energy-related products in the geologic subsurface provides reserve capacity, resilience, and security to the energy supply chain. Sequestration of energy-related products ensures long-term isolation from the environment and, for CO 2 , a reduction in atmospheric emissions. Both porous-rock media and engineered caverns can provide the large storage volumes needed today and in the future. Methods for site characterization and modeling, monitoring, and inventory verification have been developed and deployed to identify and mitigate geologic threats and hazards such as induced seismicity and loss of containment. Broader considerations such as life-cycle analysis; environment, social and governance (ESG) impact; and effective engagement with stakeholders can reduce project uncertainty and cost while promoting sustainability during the ongoing energy transition toward net-zero or low-carbon economies.
It is well known that shale can be a problematic lithology that is capable of creating issues such as tight hole and pipe stuck during a drilling operation. Shale bedding is recognized as one of the key factors that directly contributes to drilling problems. This paper focuses on shale bedding's impact on wellbore stability, which is investigated with the comparison of wellbore stability results of the shale formation with shale bedding and without shale bedding. The geomechanical simulation results show that: (1) the characteristics of wellbore stability polar plot for all well trajectories can be dramatically changed by shale bedding; (2) both well azimuth and well inclination have significant impact on wellbore stability; (3) stress dominated and shale bedding dominated wellbore breakouts can be evaluated; (4) formation strength control and shale bedding strength control wellbore stability are indentified. Based on those simulated wellbore stability characteristics, optimizations for well azimuth, well inclination, well trajectory, and mud weights can be designed for drilling operation to mitigate the potential drilling hazards.
Oil and gas companies are increasingly seeking production from more challenging reservoirs associated with costly geomechanical problems. Knowledge of in-situ rock strength is a fundamental element of geomechanical analysis for the oil and gas industry in estimating such elements as wellbore stability, solids production, hydraulic fracturing, bit selection, cap rock integrity, compaction, and subsidence studies. Specifically, this information is critical for successful drilling of directional, highly deviated, and horizontal wells. In production phase, this provides information to maximize the efficiency of wellbore perforations and hydraulic fracturing, and also assess the requirement for sand control equipment. Log-based rock strength modeling is a technique which enables estimation of in-situ mechanical rock properties from some petrophysical logs. This technique is currently the most popular approach in order to evaluate mechanical rock properties, as laboratory tests are costly and time consuming. The important rock properties which are desired to be determined include; Uniaxial Compressive Strength (UCS), friction angle and cohesion in addition to rock elastic constants (Young's modulus, Poisson's ratio, bulk modulus and shear modulus). This technique has a number of advantages over laboratory measurements of geomechanical properties including (but not limited to): availability of log data, providing continuous property profiles, possibility of modeling weak intervals, low cost, and time effectiveness. In this study, a comprehensive review of currently available empirical equations developed by different authors is provided. In addition, algorithms for all the equations are developed and subsequently coded into a specialized log data management platform designed for petrophysical and Image log Analysis, thus converting it into a powerful tool for rock property estimation for a variety of rock types and specifications.
A real-time wellbore stability analysis capability was developed to help an operator reduce high costs of nonproductive time (NPT) in an area prone to stuck pipe, lost borehole assemblies (BHAs), and lost hole sections. A multidisciplinary team created integrated processes for predrill, dynamic real-time, and post-drill modeling to help identify wellbore instability and pore pressure events that cause kicks, tight holes, and stuck pipe incidents. A Predrill wellbore stability model for the proposed well was built based on offset well data. The model enabled the identification of depth intervals and formations where there are potential wellbore stability issues. A multidisciplinary team consisting of geomechanics engineers, pore pressure specialists and drilling optimization engineers provided 24-hour monitoring of drilling parameter trends and analyzed quad-combo logging-while-drilling (LWD) data in real time to determine the health of the wellbore. This enabled calibration of the predrill model in real time, which consequently served as an ahead-of-bit prediction of undrilled sections of the well. Four wells were drilled in this project. The first two wells had lost hole sections resulting from wellbore stability challenges that caused high NPT costs. The new process was instituted on the third well which resulted in no lost time due to troubled hole sections and subsequently resulting in 30% lower well cost due to reduction in expected NPT. The same results were achieved on the fourth well, which demonstrated repeatability of the new process. The predrill model indicated that a pore pressure ramp was expected and that the operator's planned mudweight and casing program posed potential risks of formation fluid influx and hole breakout with resultant cavings falling into the wellbore. During drilling operations the expected pressure ramp was confirmed by an observed increase in connection gas and cavings across the depth intervals identified in the predrill model. This was communicated to the operator and informed their timely decision to increase the mud weight range for the hole interval and to set the casing shallower than planned to avoid potential hole problems. This multidisciplinary approach to address well challenges by integrating technology, tailored expert response, and collaboratively managed delivery helps to reduce uncertainty, improve safety, and increase efficiency of planned wells and depth intervals. The new process comprising predrill, dynamic real-time, and post-drill phases identifies drilling hazards for correct mitigation. Lessons learned during the drilling operations are documented and applied to subsequent wells for continued improvement of operational parameters and best practices.
With rising energy demand, operators in the Middle East are now focusing on developing unconventional resources. To optimize hydraulic fracture stimulation, most of these deep gas wells are required to be drilled laterally and in the direction of the minimum horizontal stress. However, this poses an increased risk of stuck pipe due to hole instability, differential sticking and skin damage due to high overbalance pressures, which makes drilling these wells challenging and costly. Another major challenge in the Middle East is lost circulation due to natural fractures in carbonate reservoirs. Lost circulation currently accounts for loss of approximately $850-900 million USD per year globally across the industry (Marinescu 2014). This paper presents a case study where a holistic approach; combining geomechanics and drilling technologies were employed to address the drilling challenges specific to unconventional and naturally fractured reservoirs. Ultimately, this approach helped the client to mitigate stuck pipe issues, while proposing a physics/engineering-basedmethodology to reduce losses by sealing fractures, hence providing a roadmap to optimized drilling and mitigation of hazards with associated Non-Productive Time (NPT). The paper demonstrates a holistic approach, combining wellbore stability analysis, managed pressure drilling (MPD) and proposes a novel physics/engineering-based methodology for addressing lost circulation challenges. A 1-D wellbore stability model is initially developed to determine the safe operating downhole pressure limits and to effectively assess the drilling risks associated with the planned wellbore orientation. By accurately determining the required bottomhole pressure to prevent wellbore stability problems, managed pressure drilling technology can be implemented to provide improved drilling hazard mitigation by enabling reduced overbalance pressures, constant bottomhole pressure, and faster reaction time by instantaneously adjusting downhole pressures. A bi-particulate bio-degradable system is used as a lost circulation material (LCM). The bigger size cylindrical particles flowing at a pre-defined rate will form a bridge or a plug across the fracture aperture, providing mechanical stability and the smaller spherical particles will seal the gaps in the bridge there by providing an effective sealing of the fracture opening. From experience, implementing these methodologies and technologies in isolation has not provided satisfactory results. This indicates that a partnership which leverages the strengths of the individual disciplines from the early planning stages is necessary to effectively address the drilling challenges posed by unconventional and naturally fractured reservoirs. For the case study highlighted in this paper, the well was drilled to TD in a timely manner, while maintaining the integrity of the hole, hence confirming the viability of this approach. In addition, the physics and engineering design workflow for bi-particulate bio-degradable LCM demonstrates how it can be effectively deployed to mitigate lost circulation without skin damage to the formation
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