Energy is an essential component for prosperity, economic growth, and development and has become a basic necessity for humans, but at the same time, it has an impact on the environment. Therefore, it is believed that, in the coming future, renewable energy will play an important part in fulfilling the energy demand. In that respect, geothermal energy will be vital as it is a continuous source of energy that is not affected by metrological conditions and can be used in power generation or domestic heating. Many countries around the globe are actively producing energy from geothermal resources. However, the extraction of the heat from the subsurface comes with challenges such as subsurface environment, wellbore instability, corrosion, loss of circulation, and cementing operation. However, one of the most challenging and critical tasks is the zonal isolation of the geothermal well. A packer is a tool that is used for the zonal isolation of a well, and at high pressure and high temperature (HPHT) conditions, which is common for geothermal wells. Most of the components of packers fail, causing well integrity issues. This paper gives a review of the forces acting on packers, testing standards, problems encountered by a packer in the HPHT subsurface environment, and designs to overcome those problems.

The critical factors that affect bottomhole stick–slip vibrations during vertical drilling operations are thoroughly investigated and analyzed in this research. Influential factors, such as rotation speed, weight on bit (WOB), bottom hole assembly (BHA) configuration, and formation properties, were studied in order to understand their part in the stick–slip phenomena. The analysis is based on a thorough review of previous research conducted on stick–slip drilling vibrations. A mathematical model was created that not only explains axial vibrations but also includes the torsional vibrations present in stick–slip occurrences, which helps with understanding the stick–slip phenomena better. This model can be used as an analytical tool to predict and evaluate the behavior of drilling systems under various operational circumstances. Furthermore, two drilling tests using a WellScan simulator were performed to validate the research findings and assess mitigation techniques’ viability. These test scenarios reflect the stick–slip vibration-producing situations, allowing us to test mitigation strategies. The finding of this study shows the effectiveness of two tactics for reducing stick–slip vibrations. First was the reduction of WOB, which successfully lowered the occurrence of stick–slip vibrations. The second was the increase in the rotation speed, which helped to control the stick–slip problem and increased the drilling speed. This study explains the complex dynamics of stick–slip vibrations during vertical drilling and offers practical, tried-and-true methods for reducing their adverse effects on drilling operations.

Geothermal wells are subjected to higher loads compared to conventional oil and gas wells due to the thermal cycles that occur during both production and non-production phases. These temperature variations can affect the cohesion of the cement within the formation and casing, creating micro-annuli channels that can ultimately compromise the integrity of the well. Therefore, this study employs an intensive finite element methodology to analyze the debonding criteria of casing–cement systems in geothermal wells by examining over 36 independent models. The wellbore cooling and heating processes were simulated using three cohesive zone models (CZM): Type I (tensile), Type II (shear), and mixed (Type I and II simultaneously). The analysis revealed that Type I debonding occurs first during cooling at a temperature of around 10 °C, while Type II is the primary failure mode during heating. Evaluations of interfacial bonding shear strength (IBSS) values indicated that the debonding of the cement would even occur at high IBSS values (3 and 4 MPa) at a differential temperature of 300 °C, while the other IBSS of 1 MPa withstands only 60 °C. However, achieving an IBSS of 4 MPa with current technology is highly unlikely. Therefore, geothermal well operation and construction must be modified to keep the differential temperature below the critical temperature at which the debonding of the cement initiates. The study also found that debonding during cooling happens at lower differential temperatures due to generally lower values for interfacial bonding tensile strength (IBTS), typically less than 1 MPa. The novelty of the study is that it provides new insights into how specific temperatures trigger different types of debonding, highlights that high IBSS values may not prevent debonding at high differential temperatures, and recommends operational adjustments to maintain temperatures below critical levels to enhance cement integrity. Additionally, this study reveals that debonding during cooling occurs at a lower differential temperature change due to the reduced value of the interfacial bonding tensile strength (IBTS).

Global warming is presently one of the most pressing issues the planet faces, with the emission of greenhouse gasses being a primary concern. Among these gasses, CO₂ is the most detrimental because, among all the greenhouse gasses resulting from anthropogenic sources, CO₂ currently contributes the largest share to global warming. Therefore, to reduce the adverse effects of climate change, many countries have signed the Paris Agreement, according to which net zero emissions of CO₂ will be achieved by 2050. In this respect, Carbon Capture and Sequestration (CCS) is a critical technology that will play a vital role in achieving the net zero goal. It allows CO₂ from emission sources to be injected into suitable subsurface geological formations, aiming to confine CO₂ underground for hundreds of years. Therefore, the confinement of CO₂ is crucial, and the success of CCS projects depends on it. One of the main components on which the confinement of the CO₂ relies is the integrity of the cement. As it acts as the barrier that restricts the movement of the sequestrated CO₂ to the surface. However, in a CO₂-rich environment, cement reacts with CO₂, leading to the deterioration of its physical, chemical, transfer, morphological, and mechanical properties. This degradation can create flow paths that enable the leakage of sequestered CO₂ to the surface, posing risks to humans, animals, and the environment. To address this issue, numerous studies have investigated the use of various additives in cement to reduce carbonation, thus enhancing the cement’s resistance to supercritical (sc) CO₂ and maintaining its integrity. This paper provides a comprehensive review of current research on cement carbonation tests conducted by different authors. It includes detailed descriptions of the additives used, testing setups, curing conditions, methodologies employed, and experimental outcomes. This study will help to provide a better understanding of the carbonation process of the cement sample exposed to a CO₂-rich environment, along with the pros and cons of the additives used in the cement. A significant challenge identified in this research is the lack of a standardized procedure for conducting carbonation tests, as each study reviewed employed a unique methodology, making direct comparisons difficult. Nonetheless, the paper provides an overview of the most commonly used temperatures, pressures, curing durations, and carbonation periods in the studies reviewed.

Torsional vibrations pose a serious challenge in drilling operations and can lead to effects such as stick-slip phenomena, tool wear, and reduced drilling efficiency. While previous research has been conducted on torsional vibrations, there is a notable gap in comparative studies that assess the scalability of downscale models to real-world drilling conditions. This study fills this gap by systematically comparing torsional vibrations in downscale and upscale drill strings under different torque conditions at three different depths, shedding light on scaling effects in drilling vibrations. Numerical simulation was carried out taking into account non-linear interactions, damping effects, and torque variations. The laboratory set-up was for a well length of 15 m and was geometrically scaled to represent an upscale well of 450 m. Certain operational parameters such as rotation speed, torque, density, and friction coefficients were modified to keep realistic dynamic behavior, and all models were run at an identical speed of rotation to enforce consistency. The results show that both the upscale and downscale models exhibited stick-slip behavior, but differences in vibration intensity and stabilization trends point out how scaling affects torsional dynamics. Notably, the upscale bit first faced higher torsional oscillation than the set rotation speed after overcoming stick-slip before stabilizing, whereas the downscale bit went through prolonged stick-slip instability before synchronization. This study enhances the understanding of scaling effects in torsional drilling vibrations, offering a foundation for optimizing experimental setups and improving predictive modeling in drilling operations.

Carbon Capture and Sequestration (CCS) is one of the most important technologies that can help many countries to reduce emissions into the atmosphere and lower their carbon footprint, which in turn can help to achieve the net-zero goal. However, when CO₂ is injected into a suitable geological formation in the subsurface during CCS operations, it is essential to ensure that the well integrity of the legacy well within the Area of Review (AoR) is maintained so that the injected CO₂ will not make its way to the shallow formation, which can ultimately contaminate the Underground Source of Drinking Water (USDW) and make it to the surface, which can have harmful effects on the environment and human health. Hence, this paper presents a semi-quantitative risk assessment framework for legacy wells within a CCS Area of Review (AoR) and for an Underground Injection Control (UIC) Class VI injection well. The method converts a Feature Event and Process screening into an interaction matrix (IM), assigns probability × severity scores using an incident potential matrix (IPM), and derives cause-and-effect metrics to rank barrier elements and wells. The legacy wells are evaluated using a 5 × 5 IM (casing, cement sheath, water composition, gas/CO₂, and USDW), and the injector is assessed using a 7 × 7 IM (adding tubing and packer). From the results, it was found that the risk levels of the Types 2 and 3 wells were the highest, while Types 4–6 clustered in the medium-to-low range, and Types 7–9 and the Class VI well were dominated by low/very low classes. Therefore, it was concluded that the level of risk associated with legacy wells in the AoR depends upon well completion, the well configuration, the number of well barriers, and the depth to which the well penetrates. It was further found that, within the multi-barrier well, the risk level of the first barrier is lower; the risk score continues to increase with each subsequent barrier above it. The most critical elements in the given risk assessment framework for legacy wells in the AoR remain the well cement sheath, casing, and USDW. Meanwhile, the components that affect the well are water composition and the presence of gas/CO₂.