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Natural gas hydrates represent a promising clean energy source with vast reserves. Their efficient development is crucial for ensuring the sustainable advancement of human society. However, wellhead instability occurred in the long-term development, which poses a significant challenge that impacts its commercial development. In the present work, the properties of hydrate-bearing sediments were experimentally investigated. It was found that the elastic modulus, cohesion, and internal friction angle of hydrate-bearing sediments exhibit an increase with the effective stress. As an example, when the effective stress increases from 0 MPa to 25 MPa, the normalized elastic modulus exhibits a rise from 1.00 to 1.36. Conversely, the Poisson’s ratio, permeability, and porosity demonstrate a decline in accordance with this trend. As an example, both normalized porosity and permeability decrease to values below 0.40 as the effective stress increases to 25 MPa. Based on the experimental results and previous work, a comprehensive model for describing the effect of both hydrate saturation and effective stress on physical parameters was obtained. Subsequently, a multi-field coupled investigation methodology was developed to evaluate wellhead stability during the long-term development of hydrate-bearing sediments, and the evolution characteristics and mechanisms of wellhead instability were numerically explored. It reveals that development operation using the vertical wellbore decomposes hydrates in the surrounding sediments only within a radius of 19.52 m, which significantly undermines the wellhead stability. Moreover, the wellhead system not only sinks with sediment subsidence but also experiences additional sinking due to the failure of bonding between the wellhead system and sediments. Furthermore, the latter accounts for a significant portion, amounting to approximately 68.15% of the total sinking under the research conditions. This study can provide methodological prerequisites for exploring the impact of various factors on wellhead stability during the long-term hydrate development process.

An unprecedented increase in earthquakes in the U.S. mid-continent began in 2009. Many of these earthquakes have been documented as induced by wastewater injection. We examine the relationship between wastewater injection and U.S. mid-continent seismicity using a newly assembled injection well database for the central and eastern United States. We find that the entire increase in earthquake rate is associated with fluid injection wells. High-rate injection wells (>300,000 barrels per month) are much more likely to be associated with earthquakes than lower-rate wells. At the scale of our study, a well's cumulative injected volume, monthly wellhead pressure, depth, and proximity to crystalline basement do not strongly correlate with earthquake association. Managing injection rates may be a useful tool to minimize the likelihood of induced earthquakes.

Wellhead backpressure is related to the wellhead fluid production, oil pumping equipment energy consumption, and surface gathering and transportation system investment. It is commonly believed that the increase of backpressure can lead to the increase of pump leakage and the decrease of oil well production; nevertheless, the appropriate increase of backpressure is conducive to the reduction of the surface investment costs and the energy consumption. Therefore, it is necessary to optimize the backpressure. In this work, the wellhead backpressure was taken as the starting point, and the surface gathering and transportation system was associated with the mechanical production system. Based on the energy conservation equation, a calculation model of the surface backpressure reflecting the amount of energy loss in the pipe flow process, and a mathematical model of the backpressure and progressing cavity pump production conditions were developed. The research results can provide guidance for the optimization of oil wells.

Sustainable use of groundwater while maintaining economic and social development is a major challenge, and the implementation of wellhead protection areas (WHPA) for public supply wells has been applied as an instrument to overcome it. This study analyzes the WHPA delineation methods: calculated fixed radius (CFR) and two solutions of the WhAEM software (USEPA, 2018 ), one analytical and one semi-analytical. We compare their results with WHPAs generated by a stochastic three-dimensional MODFLOW-MODPATH model in two scenarios: eight pumping wells operating simultaneously and a single well pumping, both at the same public drinking water supply wellfield located on a coastal plain in Jaguaruna County, south Brazil. For the specific hydrogeological settings, all methods produced satisfactory results when delineating a 50-day time-of-travel (TOT) WHPA for a single well. However, as TOT increases, uncertainties are introduced, and the precision of the results is reduced. Multiple well pumping simultaneously presented similar issues regarding uncertainties caused by three-dimensional flow complexities resulting from well interferences. Despite being the simplest method applied in terms of hydrogeological data needs, the CFR method demonstrated reliability in its results. Additionally, we present an analysis comparing the dimensions of the capture zone with the 10- and 20-year TOT WHPAs, indicating that managing the entire capture zone is the best way to protect groundwater against conservative contaminants. Finally, we compare WHPA generated by a stochastic and a deterministic model to understand how uncertainties can affect model results.

During the Deepwater Horizon disaster, a substantial fraction of the 600,000–900,000 tons of released petroleum liquid and natural gas became entrapped below the sea surface, but the quantity entrapped and the sequestration mechanisms have remained unclear. We modeled the buoyant jet of petroleum liquid droplets, gas bubbles, and entrained seawater, using 279 simulated chemical components, for a representative day (June 8, 2010) of the period after the sunken platform’s riser pipe was pared at the wellhead (June 4–July 15). The model predicts that 27% of the released mass of petroleum fluids dissolved into the sea during ascent from the pared wellhead (1,505 m depth) to the sea surface, thereby matching observed volatile organic compound (VOC) emissions to the atmosphere. Based on combined results from model simulation and water column measurements, 24% of released petroleum fluid mass became channeled into a stable deep-water intrusion at 900- to 1,300-m depth, as aqueously dissolved compounds (∼23%) and suspended petroleum liquid microdroplets (∼0.8%). Dispersant injection at the wellhead decreased the median initial diameters of simulated petroleum liquid droplets and gas bubbles by 3.2-fold and 3.4-fold, respectively, which increased dissolution of ascending petroleum fluids by 25%. Faster dissolution increased the simulated flows of water-soluble compounds into biologically sparse deep water by 55%, while decreasing the flows of several harmful compounds into biologically rich surface water. Dispersant injection also decreased the simulated emissions of VOCs to the atmosphere by 28%, including a 2,000-fold decrease in emissions of benzene, which lowered health risks for response workers.

In the development of high-pressure and high-temperature oil and gas reservoirs, the well kick phenomenon often occurs due to abnormal pressure systems, improper field operation and other reasons. During the rushing of a single pipe or vertical column for blowout prevention, the wellhead fluid flow rate is often too high, which directly affects the well control efficiency and success rate. Based on the traditional shut-in procedure and the principle of fluid mechanics, this paper analyses the dynamic change characteristics of the medium flow between the wellhead and the relief line. It proposes to open the throttle valve to divert the wellhead outflow medium when rushing to connect a single pipe or vertical column for blowout prevention. Thus, it improves the shut-in procedure under the well kick condition, and the variation law between different jet flow rates, throttle valve openings, and wellhead flow rates is obtained. The research shows that the improved shut-in method can effectively slow down the flow rate of the wellhead fluid, reduce the pressure fluctuation caused by shut-in, and provide technical support for avoiding the blowout accident caused by the unsuccessful operation of the single blowout preventer.

Ordos Basin is rich in unconventional oil and gas resources. Shale resources are developed in source rock series. With the continuous development, many oil wells have different degrees of blockage in the production process. It has different levels of complex performance in wellhead, wellbore and formation, which seriously restricts reservoir production. The formation fluid, reservoir rock samples and plugging materials were analyzed from multiple angles by means of nuclear magnetic electron microscopy, X-ray and acid dissolution to determine the source and formation mechanism of plugging materials. The analysis results show that the main component of the formation mineral is quartz, and the formation crude oil is mainly alkane. The scale sample is a mixture of formation minerals, scaling and corrosion products, and the content varies greatly. It is considered that the particle migration in the reservoir is an important cause of inorganic damage, and the organic matter damage cooperates with the inorganic damage to make the damage more serious. On this basis, this paper puts forward the organic cleaning of wellhead and wellbore, and then inorganic plugging removal of formation plugging, and constructs the deep acidification system of 12 % HCL + 10 % HBF 4 and 10 % GT-α. The experiment shows that the effective production ratio can reach 3.6, and the effect of acidizing and plugging removal is remarkable. This study has formed an effective plugging treatment technology for shale reservoir, which can provide technical support for similar reservoir acidification.

When offshore exploration wells are carried out, a narrow operating window and prolonged construction period may be encountered, which may lead to the evacuation of the drilling platform. The conductor will be left freestanding in the sea water, posing a great risk to wellhead stability. In this paper, based on finite element simulation of offshore exploratory well freestanding conductors, the stability analysis method is built and evaluation of a well is carried out. It is concluded that in 1 year return period and sea conditions by hanging load return period of 10 years of sea condition, the stability all meet the conditions, but there in 10 years return period of sea state by hanging load and 50 years return period of sea condition did not meet the requirements of stability. In cases where stability requirements are not met, alternative means of retaining the wellhead are recommended. This study has certain guiding significance for the safe and efficient operation of offshore exploration wells.

Huabei Oilfield has a wide range of oil and gas resources. With the pressure of environmental protection and the need for high-quality and cost-effective exploration and development, cluster drilling has also put forward higher requirements. In this oilfield, there is no effective technology in large cluster reservoir, integrated design of drilling and production, surface engineering, intensive construction, recycling of drilling fluid and so on. Taking a block in Bayan as the research focus, combined with geological characteristics, and by means of experiment and theoretical analysis, this paper focuses on the optimization of wellhead layout, trajectory optimization and drilling fluid recycling technology of cluster well, and forms the cluster well drilling and completion technology that is suitable for reservoir characteristics in the target area of Huabei Oilfield, so as to achieve the purpose of reducing cost and increasing efficiency, speeding up production and construction and expanding space.

Hundreds of thousands of unconventional natural gas wells recently constructed across North America have transformed the global energy landscape and generated widespread concern relating to fugitive methane leakage. To date, no studies have evaluated the integrity of unconventional wells post‐abandonment. Here, we evaluated emissions at nine decommissioned unconventional wells within the Montney region of British Columbia, Canada and found two exhibited co‐emission of CH4 and CO2 from surrounding soils indicating integrity failure, releasing up to ∼2,000 kg of CO2‐eq/yr into the atmosphere. A further three wells exhibited statistically significant anomalous CO2 fluxes of ∼500 kg/year from surficial soils around the well, likely associated with minor integrity failure and derived from near total soil‐based aerobic oxidation of fugitive CH4. These findings suggest that more than half of decommissioned unconventional wells may generate emissions, however only relatively small contributions to GHG emissions result that are significantly mitigated through natural soils‐based CH4 oxidation. Plain Language Summary We examined the integrity of decommissioned unconventional wells hosted in the Montney Play of British Columbia, Canada, with a view to constraining emission incidence rates and quantifying potential fugitive emissions to atmosphere. Through monitoring of soil gas fluxes, climatic factors and characterizing gas molecular signatures and surficial sediments, we show that out of nine unconventional wells examined two were co‐emitting small excess amounts of CH4 and CO2 while a further three were emitting excess CO2 from soils around the wellhead indicative of leakage. We conclude that while emissions from some decommissioned unconventional wells may occur, natural soils‐based oxidation may fully convert released CH4 to CO2 and significantly mitigate greenhouse gas emissions from such sources. Key Points First evaluation of leakage of methane from nine decommissioned unconventional gas wells At least five wells (56% of those examined) potentially suffering integrity loss resulting in minimal emissions Methane emissions observed are considerably mitigated through natural soils‐based oxidation