Using abandoned gas wells as geothermal resources for energy production is an effective way to extract geothermal energy from geological formations. These abandoned wells have the potential to ...significantly contribute in the rising global demand for energy without requiring the land disruption resulting from deep drilling or digging, processes necessary for energy extraction from geological formations via more traditional methods. In this paper, a method to extract geothermal energy from abandoned gas wells is proposed. The method offers an efficient, economical, and environmentally-conscious way to generate electricity. A mathematical model of a thermal and hydraulic coupling process is constructed, and a 3D numerical model is generated to study the process of geothermal energy extraction by retrofitting an abandoned gas reservoir into a geothermal reservoir. Using the model, heat extraction and fluid flow are analyzed over a period of 50 years. The heat production, electricity generation, and thermal recovery over the lifetime of the reservoir indicate that a commercially viable geothermal dual well system can produce geothermal energy effectively. Dual-well systems contain at least one injection well and one production well. They are composed of a two-way flow system in which the fluid flows into the reservoir via an injection well and returns from the production well having absorbed thermal energy from the surrounding rocks. Sensitivity analysis of the main parameters controlling the average outlet temperature of the fluid from the sedimentary geothermal system reveals that abandoned gas wells are a suitable source of geothermal energy. This energy can be harvested via a method whose use of reservoir fluids differs from that of the traditional method of closed-loop circulation via a borehole heat exchanger. Here, it is demonstrated that abandoned oil and gas fields can be repurposed to be geothermal energy sources that provide low-cost electricity and are economically sustainable.
A wide variety of well drilling techniques and well completion methods is used in the installation of dewatering and artificial recharge wells for the purpose of construction dewatering. The ...selection of the optimal well type is always a trade-off between the overall costs of well completion and development, the optimal well hydraulics of the well itself, the hydraulic impact of the well on its surroundings, and the required operational life span of the well. The present study provides an analytical framework that can be used by dewatering and drilling companies to quantify the contribution to head loss of typical dewatering and artificial-recharge well configurations. The analysis shows that the placement of partially penetrating wells in high-permeability layers could promote the use of quick and cheap installation of naturally developed wells using jetting or straight-flush rotary drilling. In high-permeability layers, such wells can be favorable over wells completed with filter pack, which require extensive well development to remove the fines from the filter cake layer. The amount of total head loss during discharge/recharge at a volumetric rate of 20 m
3
/h per meter of filter length, into or from a gravely aquifer layer, is reduced by factors of 3–4 while using naturally developed well types instead of well types completed with a filter pack that contains a filter cake layer due to borehole smearing.
Summary
Retrofitting depleted oil wells to extract geothermal energy is considered as one of the promising proposals to extend the overall economic life of oil and gas well. For successful ...implementation of this initiative, a comprehensive overview covering all aspects of geothermal energy extraction from abandoned oil well should be taken into account including technical, economic considerations as well as regulations and policies of respective local governments. Unfortunately, most reported studies have been focused only on one or two aspects, primarily on technical and economic aspects. Little or no study has focused on the policy sector. Moreover, these findings have been scattered, creating difficulties to extract essential information and dragging further development of the technology. This paper is therefore prepared with the objective to provide a comprehensive overview on the geothermal energy extraction from abandoned oil well, technical challenges in its implementation, economical consideration on the conversion of the well and government policy on energy especially geothermal energy and regulation on the utilization of abandoned oil well. To achieve this objective, extensive literature reviews are conducted with more attention given to recent studies on the field. Challenges on the development of this technology are discussed from technical, economic, and policy perspectives. Based on the identified challenges, required research and development as well as necessary policies for further advancement of this technology are outlined and discussed. By providing this comprehensive information, this review paper may serve as a good foundation and guidelines on the conversion of abandoned oil wells into geothermal energy wells.
Horizontal wells play an often overlooked role in hydrogeology and aquifer remediation but can be an interesting option for many applications. This study reviews the constructional and hydraulic ...aspects that distinguish them from vertical wells. Flow patterns towards them are much more complicated than those for vertical wells, which makes their mathematical treatment more demanding. However, at some distance, the drawdown fields of both well types become practically identical, allowing simplified models to be used. Due to lower drawdowns, the yield of a horizontal well is usually higher than that of a vertical well, especially in thin aquifers of lower permeability, where they can replace several of the latter. The lower drawdown, which results in lower energy demand and slower ageing, and the centralized construction of horizontal wells can lead to lower operational costs, which can make them an economically feasible option.
Casing and cement impairment in oil and gas wells can lead to methane migration into the atmosphere and/or into underground sources of drinking water. An analysis of 75,505 compliance reports for ...41,381 conventional and unconventional oil and gas wells in Pennsylvania drilled from January 1, 2000—December 31, 2012, was performed with the objective of determining complete and accurate statistics of casing and cement impairment. Statewide data show a sixfold higher incidence of cement and/or casing issues for shale gas wells relative to conventional wells. The Cox proportional hazards model was used to estimate risk of impairment based on existing data. The model identified both temporal and geographic differences in risk. For post-2009 drilled wells, risk of a cement/casing impairment is 1.57-fold 95% confidence interval (CI) (1.45, 1.67); P < 0.0001 higher in an unconventional gas well relative to a conventional well drilled within the same time period. Temporal differences between well types were also observed and may reflect more thorough inspections and greater emphasis on finding well leaks, more detailed note taking in the available inspection reports, or real changes in rates of structural integrity loss due to rushed development or other unknown factors. Unconventional gas wells in northeastern (NE) Pennsylvania are at a 2.7-fold higher risk relative to the conventional wells in the same area. The predicted cumulative risk for all wells (unconventional and conventional) in the NE region is 8.5-fold 95% CI (7.16, 10.18); P < 0.0001 greater than that of wells drilled in the rest of the state.
Hydraulic fracturing operations are generating considerable discussion about their potential to contaminate aquifers tapped by domestic groundwater wells. Groundwater wells located closer to ...hydraulically fractured wells are more likely to be exposed to contaminants derived from on-site spills and well-bore failures, should they occur. Nevertheless, the proximity of hydraulic fracturing operations to domestic groundwater wells is unknown. Here, we analyze the distance between domestic groundwater wells (public and self-supply) constructed between 2000 and 2014 and hydraulically fractured wells stimulated in 2014 in 14 states. We show that 37% of all recorded hydraulically fractured wells stimulated during 2014 exist within 2 km of at least one recently constructed (2000–2014) domestic groundwater well. Furthermore, we identify 11 counties where most (>50%) recorded domestic groundwater wells exist within 2 km of one or more hydraulically fractured wells stimulated during 2014. Our findings suggest that understanding how frequently hydraulic fracturing operations impact groundwater quality is of widespread importance to drinking water safety in many areas where hydraulic fracturing is common. We also identify 236 counties where most recorded domestic groundwater wells exist within 2 km of one or more recorded oil and gas wells producing during 2014. Our analysis identifies hotspots where both conventional and unconventional oil and gas wells frequently exist near recorded domestic groundwater wells that may be targeted for further water-quality monitoring.
Millions of abandoned oil and gas wells are scattered across the United States, causing methane emissions and other environmental hazards. Governments are increasingly interested in decommissioning ...these wells but want to do so efficiently. However, information on the costs of decommissioning wells is very limited. In this analysis, we provide new cost estimates for decommissioning oil and gas wells and key cost drivers. We analyze data from up to 19,500 wells and find median decommissioning costs are roughly $20,000 for plugging only and $76,000 for plugging and surface reclamation. In rare cases, costs exceed $1 million per well. Each additional 1,000 feet of well depth increases costs by 20%, older wells are more costly than newer ones, natural gas wells are 9% more expensive than wells that produce oil, and costs vary widely by state. Surface characteristics also matter: each additional 10 feet of elevation change in the 5-acre area surrounding the well raises costs by 3%. Finally, we find that contracting in bulk pays: each additional well per contract reduces decommissioning costs by 3% per well. These findings suggest that regulators can adjust bonding requirements to better match the characteristics of each well.
Recent work indicates that oil and gas methane (CH4) inventories for the United States are underestimated. Here we present results from direct measurements of CH4 emissions from 138 abandoned oil and ...gas wells, a source currently missing from inventories. Most abandoned wells do not emit CH4, but 6.5% of wells had measurable CH4 emissions. Twenty‐five percent of wells we visited that had not been plugged emitted > 5 g CH4 h−1. Stable isotopes indicate that wells emit natural gas and/or coalbed CH4. We estimate that abandoned wells make a small contribution (<1%) to regional CH4 emissions in our study areas. Additional data are needed to accurately determine the contribution of abandoned wells to national CH4 budgets, particularly measurements in other basins and better characterization of the abundance and regional distribution of high emitters.
Key Points
Abandoned wells are likely a minor source of methane in four production regions
Plugging of inactive wells may be an effective means to reduce gas leakage
Coalbed and natural gas methane both contribute to emissions from abandoned wells
We analyze the co-seismic groundwater level responses to four great earthquakes recorded by China's network of groundwater monitoring wells. The large number of operational wells (164 wells for the ...2007 Mw 8.5 Sumatra earthquake, 245 wells for the Mw 7.9 Wenchuan earthquake, 228 wells for the Mw 9.0 Tohoku earthquake and 223 wells for 2012 Mw 8.6 Sumatra earthquake) and co-seismic responses provide an opportunity to test hypotheses on mechanisms for co-seismic water level changes. Overall, the co-seismic water level responses are complex over large spatial scales, and there is great variability both in the sign and amplitude of water level responses in the data set. As shown in previous studies, permeability change, rather than static strain, is a more plausible mechanism to explain most of the co-seismic responses. However, we find through tidal analysis of water level responses to solid Earth tide that only one third of these wells that showed a sustained post-seismic response can be explained by earthquake-induced permeability change in aquifers, and these wells had sustained (>30 days) water level changes. Wells that did not show sustained changes are more likely affected by permeability changes only immediately adjacent to the wellbore.
•Co-seismic responses to four great Asian earthquakes across were reported.•The data compilation covers large spatial scales and multiple earthquakes.•We quantify their characteristics, and evaluate their mechanisms.•Many water level changes are a consequence of permeability changes in the well bore and not aquifers.
Data from around the world (Australia, Austria, Bahrain, Brazil, Canada, the Netherlands, Poland, the UK and the USA) show that more than four million onshore hydrocarbon wells have been drilled ...globally. Here we assess all the reliable datasets (25) on well barrier and integrity failure in the published literature and online. These datasets include production, injection, idle and abandoned wells, both onshore and offshore, exploiting both conventional and unconventional reservoirs. The datasets vary considerably in terms of the number of wells examined, their age and their designs. Therefore the percentage of wells that have had some form of well barrier or integrity failure is highly variable (1.9%–75%). Of the 8030 wells targeting the Marcellus shale inspected in Pennsylvania between 2005 and 2013, 6.3% of these have been reported to the authorities for infringements related to well barrier or integrity failure. In a separate study of 3533 Pennsylvanian wells monitored between 2008 and 2011, there were 85 examples of cement or casing failures, 4 blowouts and 2 examples of gas venting. In the UK, 2152 hydrocarbon wells were drilled onshore between 1902 and 2013 mainly targeting conventional reservoirs. UK regulations, like those of other jurisdictions, include reclamation of the well site after well abandonment. As such, there is no visible evidence of 65.2% of these well sites on the land surface today and monitoring is not carried out. The ownership of up to 53% of wells in the UK is unclear; we estimate that between 50 and 100 are orphaned. Of 143 active UK wells that were producing at the end of 2000, one has evidence of a well integrity failure.
•Oil and gas well barrier elements can fail.•The percentage of wells with barrier element failure is between 1.9% and 75%.•Pennsylvanian shale wells have well barrier and failures rates of 6.3% or less.
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