Search Results (17)

In petroleum exploration and production, lost circulation not only significantly increases exploration and development costs and operational cycles but may also lead to major incidents such as wellbore instability or even project abandonment. This paper constructs a polymer gel plugging system by optimizing high-molecular-weight polymers, crosslinker systems, and resin hardeners. The optimized system composition was determined as 1% polymer J-1, 0.3% catechol, 0.6% hexamethylenetetramine (HMTA), and 15% urea–formaldehyde resin. Experimental studies demonstrated that during the initial stage (0–3 days) at 120 °C, the optimized gel system maintained a storage modulus (G′) of 17.5 Pa and a loss modulus (G″) of 4.3 Pa. When the aging period was extended to 9 days, G′ and G″ decreased to 16 Pa and 4 Pa, respectively. The insignificant reduction in gel strength indicates excellent thermal stability of the gel system. The gel exhibited superior self-filling capacity during migration, enabling complete filling of fractures of varying sizes. After aging for 1 day at 120 °C, the plugging capacity of the gel system under water flooding and gas flooding conditions was 166 kPa/m and 122 kPa/m, respectively. Furthermore, a complete gel barrier layer formed within a 6 mm wide vertical fracture, demonstrating a pressure-bearing capacity of 105.6 kPa. This system shows good effectiveness for wellbore isolation and fracture plugging. The polymer gel plugging system studied in this paper can simplify lost circulation treatment procedures while enhancing plugging strength, providing theoretical support and technical solutions for addressing lost circulation challenges. Full article

With the intensive development of oil and gas resources leading to a rapid increase in abandoned wells, sealing failures may cause oil and gas leakage and environmental pollution. Systematically investigating the temperature distribution patterns of thermite melting in open-hole abandoned wells under various factors is critical for effective plugging. This study overcomes the limitations of traditional single heat conduction models by integrating thermite reaction kinetics, phase change latent heat, and thermal–fluid–solid multi-field coupling effects, establishing a thermal–fluid–solid coupling model for thermite melting in open-hole abandoned wells. This model provides theoretical guidance for the effectiveness of plugging operations and temperature control during operations. The model was validated through thermite melting experiments: the simulated expansion of the sandstone borehole diameter was 9.8 mm, with a 5.5% error compared to the experimental value of 9.29 mm; and the simulated axial extension at the well bottom was 18.9 mm, with a 4.7% error compared to the experimental value of 17.19 mm, confirming the model’s accuracy. The influence of different lithologies and initial downhole temperatures on the temperature distribution in the open-hole section of abandoned wells under identical conditions was analyzed. The results show that the ultimate melting thicknesses of dolomite, limestone, and granite are 0.0354 m, 0.0350 m, and 0.0234 m, respectively, indicating superior plugging effects in dolomite and limestone. In the initial reaction stage (stage a), the phase change thickness of limestone exceeded that of dolomite by 59.78%, demonstrating better thermite melting and sealing efficacy in limestone. Additionally, model analysis reveals that the initial downhole temperature has a minimal impact on the temperature distribution of thermite melting in open-hole abandoned wells. Full article

Portland cement is the primary barrier material for well abandonment. However, the limitations of cement, especially under harsh downhole conditions, are necessitating research into alternative barrier materials. While several alternatives have been proposed, the screening process leading to their selection is scarcely discussed in the literature, resulting in the non-repeatability of the selection process. This study develops a dynamic multi-criteria decision-making technique for assessing the material options for the abandonment of high-pressure high-temperature (HPHT) wells with exposure to harsh reservoir fluids. The material screening process is performed in ANSYS Granta and a combined technique for order of preference by similarity to ideal solution (TOPSIS) and analytical hierarchy process (AHP) approach is used for ranking the shortlisted material alternatives based on seven material properties proven in the literature to be critical to the long-term integrity of well barrier materials. Nine alternative materials are ranked against Portland cement and high alumina cement. The results show that the top-ranking materials are from the phenol formaldehyde and polyamide–imide groups. Of these, the primary production CO₂ of the polyamide–imide is, on average, about 25 times higher than the primary production CO₂ of the phenol formaldehyde material. A sensitivity analysis of the methodology confirms that the criteria with the highest initial weights are the most impactful in terms of the final rank. The material property values also have an impact on the extent to which variations in their weights affect the hierarchical position of the materials in the TOPSIS-AHP analysis. Despite their higher cost per unit volume, the alternative materials consistently outperformed cement—even when average price was weighted more heavily than the most influential mechanical property. Full article

Salt caverns serve as underground storage for crude oil, natural gas, compressed air, carbon dioxide, and hydrogen. Key stages of cavern development for storage purposes include design, construction, storage, and abandonment. The design phase addresses optimal cavern shape, size, pillar dimensions, number of caverns, the impact of interbeds, and cyclic loading while considering the creep behavior of salt and the mechanical behavior of surrounding layers. During this phase, geological factors such as depth, thickness, and the quality of salt are considered. For construction, two main methods—direct leaching and reverse leaching—are chosen based on design specifications. The storage stage includes the injection and withdrawal of gases in a cyclic manner with specific injection rates and pressures. After 30 to 50 years, the caverns are plugged and abandoned. The geological limitation of salt domes makes it essential to look for more bedded evaporites. This study provides a comprehensive review of bedded evaporites, including their origin and depositional environment. The stability of caverns in all these stages heavily relies on geomechanical analysis. Factors affecting the geomechanics of bedded salts such as mineralogy, physical properties, and mechanical properties are reviewed. A list of bedded evaporites in the U.S. and Canada, including their depth, thickness, and existing caverns, is provided. Additionally, this study discusses the main geomechanical considerations influencing design, solution mining, cyclic loading, and abandonment of caverns in bedded salt caverns. Full article

Palygorskite has shown satisfactory performance in salted water-based fluids, especially as a rheological agent. However, this type of formulation has been used in the petroleum industry only in well drilling operations. This study proposes the development of a salted water-based fluid with palygorskite, which presents an adequate performance as a liquid barrier element in temporary abandonment operations of wells. Based on a factorial design, seven fluid formulations were prepared with varying concentrations of palygorskite and PAC LV and were tested by measuring the HPHT filtrate volume, rheological properties, density, and pH. For comparison purposes, the results of the seven formulations were evaluated against a formulation without palygorskite and analyzed for their performance in abandonment operations. The results showed that the presence of palygorskite reduces filtrate volumes by at least 21%, thereby helping control the pressure exerted by the fluid column, which is the primary requirement for abandonment operations. Furthermore, the fluid that contained the highest amount of palygorskite and PAC LV (20 g and 8 g, respectively) showed the best results regarding filtrate control (11.2 mL) and solid sedimentation. Therefore, it is a very promising alternative for use as a well barrier element in the temporary abandonment of wells. Full article

Plug and abandonment of offshore oil wells is a costly and time-consuming process, yet it is necessary for the ever-increasing number of mature fields in the region of the Danish North Sea, as well as globally. Current practices ensuring durable solutions for the complete zonal isolation of oil wells have a large environmental impact. This paper proposes a novel resin that could be mixed on the platform and pumped into the tubing in a liquid state. The increased temperature inside the oil well initiates the cross-linking reaction of the liquid resin, creating a solid and impermeable barrier. The liquid resin is thermally stable up to 180 °C and can be handled for up to 20 h at room temperature, preventing setting before intended while decreasing environmental impact. The solid resin has a compressive strength of 54 MPa and a steel adhesion strength of 6.27 MPa, highlighting its ability to withstand extreme downhole conditions. Full article

Orphaned and abandoned wells in the United States pose significant environmental risks, including methane emissions, groundwater contamination, and ecosystem degradation. These wells also threaten the integrity of carbon capture and storage (CCS) projects by providing potential leakage pathways for stored CO₂, particularly if they lack proper plugging and well integrity. Although the exact number of orphaned and abandoned wells is uncertain due to poor historical documentation, recent estimates suggest there could be as many as 3.9 million such wells nationwide, emitting approximately 3.2 Teragram (Tg) of methane annually. This study investigates the distribution of orphaned and abandoned wells across the United States, presenting new estimates of documented wells and exploring their methane emissions. Through state-level data analysis, the number of documented orphan wells is estimated to be significantly higher than previously reported. A machine learning model, specifically a RandomForestRegressor, was employed to predict the locations of potential orphan wells, enhancing the ability to target monitoring and remediation efforts. Full article

Plug and abandonment (P&A) operations demand valuable time and resources for operational procedures and materials to establish the well barrier element. This study aims to investigate the application of a water-based fluid as a liquid well barrier element for temporary abandonment, based on estimates of its lifespan and the survival probabilities of downhole temperatures acquired through accelerated life tests. To achieve this, the water-based formulation was tested and exposed to 95, 110, 140, and 150 °C temperatures for time intervals ranging from 1 to 10 days. After the temperature exposure, the fluid properties were verified, and failure was detected by accounting for any deterioration in rheological parameters and/or a substantial increase in filtrate volume. A statistical analysis of the failure data was performed in RStudio 4.1.3 software using the Weibull Model, and the fluid average lifespans and survival probabilities were estimated for the P&A temperatures. The results obtained demonstrate that the degradation of the fluid was only observed for 140 and 150 °C temperatures. According to the results, the fluid is a promising alternative for temporary abandonment until 80 °C, with no need for monitoring once its lifetime expectation exceeds three years at this temperature. For downhole temperatures above 80 °C, the fluid is a possible alternative, however, the operation’s maximum time and monitoring requirements should consider reliability metrics for each temperature. Full article

This study aims to evaluate how the operational procedure adopted for pellet placement and the exposure to subsurface conditions influence the mechanical integrity of bentonite plugs used as barrier elements in the abandonment of petroleum wells. To this end, the plugs were formed by hydrating the pellets directly in water, simulating the onshore procedure, while the offshore plugs were obtained from pellets hydrated in deionized water after immersion in diesel or olefin, which are suggested as displacement fluids. The plugs obtained were tested by compression and adhesion tests. These mechanical tests were also carried out for specimens obtained from plugs exposed to four formulations of synthetic formation waters. The results obtained demonstrated that, in the offshore procedure, the previous contact with olefin may adversely affects the mechanical stability of bentonite plugs, while plugs formed from pellets immersed in diesel presented satisfactory mechanical properties. However, the contact with formation water evidenced that the onshore plug presents superior resistance than the offshore plug previously immersed in diesel. The highly successful performance of the onshore plug was attested by the maintenance of the compressive strength, which exhibited a maximum reduction of 13%, even after exposure to the most saline formation waters. Full article

Background: The clinical management of teeth with complex dens invaginatus (DI) malformations and apical periodontitis may be challenging due to the lack of routine. The aim of this case report is to describe the endodontic treatment of an immature tooth with DI and to discuss strategies for preclinical training for teeth with such malformations. Case report: A 9-year-old male presented with an immature maxillary incisor with DI (Oehlers Type II) and apical periodontitis which was diagnosed by cone beam computed tomography (CBCT). Revitalization was initially attempted but then abandoned after failure to generate a stable blood clot. Nevertheless, considerable increase in both root length and thickness could be detected after medication with calcium hydroxide followed by root canal filling with MTA as an apical plug. Conclusions: The endodontic management of teeth with DI requires thorough treatment planning. In immature teeth, under certain conditions, root maturation may occur even with conventional apexification procedures. From an educational perspective, different strategies including CBCT and 3D-printed transparent tooth models for visualization of the complex internal morphology and redesigned 3D-printed replica with various degrees of difficulty for endodontic training, can be used to overcome the challenges associated with endodontic treatment of such teeth. Full article

With the development of oil exploration, the number of complex situations encountered in the drilling process is continuously increasing. During the operation of large displacement and horizontal wells, the safe density window of drilling fluid is narrow in complex formations and the lost circulation problem is becoming increasingly prominent. This can easily cause the drilling fluid to enter the formation from inside the well through lost circulation channels, which will prolong the drilling cycle, increase drilling costs, affect geological logging, and could cause a series of malignant accidents (such as blowout, sticking of a drilling tool, borehole collapse, and well abandoned). According to the severity, common lost circulation can be classified into three types: fractured lost circulation, karst cave lost circulation, and permeability lost circulation. Currently, researchers are developing different types of lost circulation materials (LCMs) for various lost circulation situations. Compared with conventional lost circulation control methods, the polymer gel lost circulation control technique applies a three-dimensional cage-like viscoelastic body formed via the crosslinking reaction of polymer gels. These materials have strong deformability and can enter fractures and holes through extrusion and deformation without being restricted by lost circulation channels. They then settle in the lost circulation formation and form a plugging layer through a curing reaction or swelling effect. Among the polymer gel LCMs, high-temperature resistant polymer gels can either be used alone or in combination with other LCMs, bringing the advantages of adjustable gelation time, strong lost circulation control ability, and strong filtration ability of the plugging slurry. Moreover, they are suitable for the lost circulation control of microporous leaky layer and have limited influence on the performance of drilling fluids. Therefore, the high-temperature resistant polymer gel lost circulation control technique is increasingly becoming a hot spot in the research of LCMs nowadays. This paper summarizes the research progress into high-temperature resistant functional gels for profile control and water shutoff, lost circulation prevention and control, and hydraulic fracturing. Furthermore, the current application status of high-temperature resistant gels and high-temperature resistant gel temporary plugging agents is demonstrated, followed by a detailed overview of the gel-breaking methods. Overall, this research lays the theoretical foundation for the application and promotion of high-temperature resistant gels. Full article

Wellbore-plugging materials are threatened by challenging plugging and abandonment (P&A) conditions. Hence, the integrity and resilience of these materials and their ability to provide sufficient zonal isolation in the long-term are unknown. The present work focuses on investigating the potential to use zeolites as novel additives to the commonly used Class-H cement. Using four different zeolite–cement mixtures (0%, 5%, 15% and 30%, by weight of cement) where samples were cast as cylinders and cured at 90 °C and 95% relative humidity, the unconfined compressive strength (UCS) testing showed a 41% increase with the 5% ferrierite addition to the Class-H cement in comparison to neat Class-H cement. For triaxial compression tests at 90 °C, the highest strength achieved by the 5% ferrierite-added formulations was 68.8 MPa in comparison to 62.9 MPa for the neat Class-H cement. The 5% ferrierite formulation also showed the lowest permeability, 13.54 μD, which is in comparison to 49.53 μD for the neat Class-H cement. The overall results show that the 5% ferrierite addition is the most effective at improving the mechanical and petrophysical properties based on a water/cement ratio of 0.38 when tested after 28 days of curing in 95% relative humidity and 90 °C. Our results not only demonstrate that zeolite is a promising cement additive that could improve the long-term strength and petrophysical properties of cement formulations, but also provide a proposed optimal formulation that could be next utilized in a field trial. Full article

Reservoir formation waters typically contain scaling ions which can precipitate and form mineral deposits. Such mineral deposition can be accelerated electrochemically, whereby the application of potential between two electrodes results in oxygen reduction and water electrolysis. Both processes change the local pH near the electrodes and affect the surface deposition of pH-sensitive minerals. In the context of the plugging and abandonment of wells, electrochemically enhanced deposition could offer a cost-effective alternative to the established methods that rely on setting cement plugs. In this paper, we tested the scale electro-deposition ability of six different formation waters from selected reservoirs along the Norwegian continental shelf using two experimental setups, one containing CO₂ and one without CO₂. As the electrochemical deposition of scaling minerals relies on local pH changes near the cathode, geochemical modelling was performed to predict oversaturation with respect to the different mineral phases at different pH values. In a CO₂-free environment, the formation waters are mainly oversaturated with portlandite at pH > 12. When CO₂ was introduced to the system, the formation waters were oversaturated with calcite. The presence of mineral phases was confirmed by powder X-ray diffraction (XRD) analyses of the mineral deposits obtained in the laboratory experiments. The geochemical-modelling results indicate several oversaturated Mg-bearing minerals (e.g., brucite, dolomite, aragonite) in the formation waters but these, according to XRD results, were absent in the deposits, which is likely due to the significant domination of calcium-scaling ions in the solution. The amount of deposit was found to be proportional to the concentration of calcium present in the formation waters. Formation waters with a high concentration of Ca ions and a high conductivity yielded more precipitate. Full article

Existing buildings are characterized by the continuous change in the functional requirements of their end-users. As such, they are subjected to renovation or reconstruction, which is associated with total or partial demolition of the buildings, leading to an increase in construction and demolition waste. In addition, the materials abandoning the circular loop leave an adverse impact on the environment. This research integrates the building information modeling (BIM) approach and lean principles to ensure the early involvement of key participants in the decision-making process. This approach aids in planning the sequencing of deconstruction planning phases required before actual demolition activities take place. The paper presents the practical implementation of a BIM plug-in Tool. The assumptions and the scope based on which the plug-in was designed are briefly discussed. A case study for a mechanical, electrical, and plumbing (MEP) BIM model is introduced to illustrate the practical features of the proposed BIM plug-in Tool. The results encourage the selective dismantling of building elements based on the customers’ needs. Building information modeling capabilities in deconstruction planning were also investigated. The proposed tool aids in decreasing the uncertainties involved in demolition projects. The tool can be implemented on a national level to automate the deconstruction projects and optimize the extraction of salvaged building elements. The recovery option for such elements and their final destiny can be secured with sufficient time before their dismantling from their original locations. Full article

Utilization of natural shale formations for the creation of annular barriers in oil and gas wells is currently discussed as a mean of simplifying cumbersome plugging and abandonment procedures. Shales that are likely to form annular barriers are shales with high content of swelling clays and relatively low content of cementation material (e.g., quartz, carbonates). Shales with large content of quartz and low content of swelling clays will be rather brittle and not easily deformable. In this paper we ask the question whether and to what extent it is possible to modify the mechanical properties of relatively brittle shales by chemically removing some cementation material. To answer this question, we have leached out carbonates from Pierre I shale matrix using hydrochloric acid and we have compared mechanical properties of shale before and after leaching. We have also followed leaching dynamics using X-ray tomography. The results show that removal of around 4–5 wt% of cementation material results in 43% reduction in Pierre I shale shear strength compared to the non-etched shale exposed to sodium chloride solution for the same time. The etching rate was shown to be strongly affected by the volume of fluid staying in direct contact with the shale sample. Full article