Numerical study of underground CO2 storage and the utilization in depleted gas reservoirs

The emission of atmospheric CO2 is the main contributor to global warming and climate change. Carbon capture and storage (CCS) is considered as the most promising technology for slowing down the atmospheric CO2 emissions. Meanwhile, CCS is beneficial for the circulation carbon economy. However, CCS has not been implemented on large scale because of the related risks and the lack of economic incentives. This thesis attempts to focus on these two problems and provide some strategies to address them. Regarding the risks associated with CCS, a parametric uncertainty analysis for CO2 storage was conducted and the general role of different geomechanical and hydrogeological parameters in response to CO2 injection was determined. Regarding the financial incentives of CCS operation, this thesis attempts to increase the cost-effectiveness of CCS through co-injecting CO2 with impurities associated with enhanced gas recovery (CSEGR) and using CO2 as cushion gas in the underground gas storage reservoir (UGSR). In order to understand the thermal-hydrological-mechanical (THM) process of CO2 storage, the THM coupled simulator TOUGH2MP (TMVOC)-FLAC3D was developed. By using the developed TOUGH2MP (TMVOC)-FLAC3D simulator, numerical simulation for hundreds of sampled data was performed for results generated by the Quasi-Monte Carlo method. Based on the simulation results, the general role of different geomechanical and hydrogeological parameters was determined in response to CO2 injection using distance correlation. In addition, a risk factor was defined to characterize the risks of the caprock due to CO2 injection. The results showed that the reservoir permeability and the injection rate are the two most important factors in determining the pressure change. Moreover, the reservoir Young’s modulus plays the most vital role in formation deformation including vertical displacement. The pressure change exhibits a much closer correlation with the risk factor in comparison to the formation deformation, indicating the importance of pressure change in the integrity assessment of the caprock. By using the machine learning approach in support vector regression (SVR), the SVR surrogate model was well-trained based on the data regarding simulated results, and its reliability was verified using the test data. Thereafter, the formation response including the pressure change as well as formation deformation, can be predicted using the trained SVR surrogate model within a very short time. The methods and working scheme applied in this work can be used to guide time and effort spent mitigating the uncertainty in these parameters to acquire trustworthy model forecasts and risk assessments in CCS projects. Attempting to decrease the cost of CCS operation, CO2 injection with impurity gas, i.e., N2 and O2, into a depleted gas reservoir was investigated. The impacts of the key parameters on the performance of CO2 storage and CSEGR were analyzed in detail. The results showed that the effect of impurities on CO2 storage capacity is dependent on the reservoir pressure and temperature conditions, and the concentration of impurities. The depleted gas reservoir with a relatively low temperature and low irreducible water saturation is favorable to the CO2 storage capacity. A low primary gas recovery for the depleted gas reservoir is in favor of CSEGR, while it is suitable for dedicated CO2 storage when the primary gas recovery is high. In addition, it is suggested to produce the CH4 as possible before the operation of CO2 storage and CSEGR. The chromatographic partitioning phenomenon may occur when N2 and O2 were co-injected with CO2 into depleted gas reservoirs, which could be used as a monitoring strategy for the CO2 front and potential CO2 leakage. In addition to the solubility and concentration of the impurity gas would affect this phenomenon, there is a critical water saturation for the occurrence of significant chromatographic partitioning phenomenon associated with determined type and concentration of impurity gas. To increase the cost-effectiveness of CCS, the suitability of utilizing CO2 as the cushion gas in the UGSR was analyzed based on the geological parameters of Donghae depleted gas reservoir in Korea. The cyclic CH4 production and injection were conducted over a period of 15 years to acquire the mixing behavior of CO2 and CH4 in a relatively long-term period. The results showed that the maximum CO2 concentration that can be used for cushion gas is 9% under the condition of production and injection for 120 and 180 days in a production cycle at a rate of 4.05 and 2.7 kg/s, respectively. The typical curve of the mixing zone thickness can be divided into four stages, i.e., the increasing stage, smooth stage, suddenly increasing stage, and periodic change stage. The CO2 fraction in the UGSR, reservoir permeability, and production rate have a significant effect on the breakthrough of CO2 in the production well, while the effect of water saturation and temperature is neglectable. For the purpose of utilizing more CO2 as cushion gas in the UGSR, CO2 is supposed to be injected for supplementation during the operation of UGSR. Generally, the parametric uncertainty analysis conducted in this thesis is beneficial for the risk assessments in CCS projects. Co-injecting CO2 with impurities associated with CSEGR and utilizing CO2 as cushion gas in UGSR are favorable for improving the economic incentives of CCS operation. Therefore, this thesis is beneficial for promoting the application of CCS and mitigating the atmospheric CO2 emissions

Seismic Expressions of Paleokarst

Paleokarst are characterized by epigene and/or hypogene processes in their formation and hold significant numbers of hydrocarbons and other natural resources. This dissertation examines worldwide seismic expression of paleokarst; and specifically, the characterization of paleokarst reservoirs developed across the Cherokee Platform, and in the Arkoma Basin, Oklahoma. Worldwide subsurface paleokarst formations are of Precambrian to Miocene age and found at depths less than 200 m to as great as 8000 m. Karst can be are expressed on seismic records as sinkholes, paleocave collapse, and tower morphologies. Seismic modeling indicates that karst can be modeled and imaged to better understand its subsurface architecture. High variance, negative curvature, bright amplitudes/localized bright spots characterize karst. As part of this dissertation, a worldwide map of paleokarst locations was generated, and geophysical measurements for some of these locations were taken for further analysis. In the Arkoma Basin, the Ordovician Viola Limestone, Mississippian Caney Shale, Pennsylvanian Jefferson Sandstone and Wapanucka Limestone were mapped on seismic data, and paleokarst sinkhole and pipe features were identified. Viola sinkholes can be recognized as structural depressions, characterized by higher seismic variance, and lower positive amplitude, and most-negative curvature. Wapanucka sinkhole features are subtle, show lower variance and higher positive amplitude, and no structural relief. The Ordovician sinkholes are coincident with the Pennsylvanian Wapanucka Limestone which are 610 m apart, with some of these sinkhole features occurring over vertical pipe features. The Viola sinkholes and pipe features are inferred to be a mature epigene karst system. The Wapanucka sinkholes are interpreted as an immature karst system with epigene and hypogene elements. This study indicates for the first-time evidence of pipe features that extend from the Ordovician into the Mississippian, and the presence of Wapanucka sinkhole features in the Arkoma Basin of Oklahoma. In the Cherokee Platform, the term Chat designates residual chert which is either in place or transported, formed by an epigene process, and found above the Miss Lime. The tripolite is internal to the Mississippi Lime formed by in place alteration of the limestone by epigene and/or hypogene processes. I have classified and mapped Chat and tripolitic chert (tripolite) zones by seismic evaluation calibrated by well control with full-wave sonic log data. Chat and tripolite show clear separation on total acoustic impedance from Miss Lime, but no separation with VP /VS, and both exhibit total porosities greater than 20 % with an indication of fracture porosity. Sonic-based normal incidence wedge models for Chat bounded above by Pennsylvanian Shale and below by Miss Lime indicate two seismic expressions are probable: a strong negative amplitude when Chat thickness is above tuning and a weak or non-existent amplitude associated with small impedance contrast between Chat and overlying Pennsylvanian shale. This analysis suggests both the traditional Chat ‘strong response’ and a new ‘dim-out’ exploration approach. Tripolite response is consistently a negative amplitude event that strengthens with increasing tripolite thickness. This study provides an interpretive framework for characterizing Chat and tripolite zones associated with the Mississippian Lime in the US Midcontinent, which may be applicable to areas around the world

Overpressure in the Central North Sea

The Central Graben of the North Sea is characterised by high levels of overpressure. This causes drilling problems and may control the migration and entrapment of hydrocarbons. Pressure measurements from repeat formation tests, mud weight and drilling gas levels have been compiled and interpreted, and integrated with the structural, lithostratigraphic and diagenetic framework of the basin. Interpretation of this data reveals that Jurassic sandstones in the region are divided into a boxwork of pressure cells. These are bodies of rock which are internally in hydraulic communication but externally isolated from adjacent cells by pressure seals. Pressure seals in the region are lithological and vary with depth, in contrast to previous hypotheses of diagenetic or temperature controls. The magnitude of overpressure in a pressure cell is controlled by the structural position of the cell, with high overpressures (close to the lithostatic pressure) occurring in structurally-elevated cells on an axial horst. Lateral hydraulic communication between deep regions and structurally-elevated positions increases the fluid pressure in the permeable sandstones in the elevated regions. This leads to focused vertical fluid flow through the thin aquitard at these elevated regions, which are termed "Leak Points". Here, the pressure seal occurs at the top of the permeable Jurassic sandstone, while in adjacent off-structure regions the pressure seal occurs in the Kimmeridge Clay Fm., the region's petroleum source rock. Analysis of density and sonic log data demonstrates excess mudstone porosity in the overpressured cells, suggesting that disequilibrium compaction is a cause of overpressure in the region. The location of pressure seals within gas-mature source rocks suggests hydrocarbon generation may also play an important role in causing overpressure. Quantitative computer modelling of the basin supports the data-driven model, emphasising lateral flow in Jurassic sandstones beneath the pressure seal and focused vertical flow across formations at structurally-elevated points. The model shows that rapid Cenozoic sedimentation, coupled to low permeability of the mudstone- dominated basin, has led to disequilibrium compaction due to restricted fluid flow. The model suggests that overpressuring began at 40 Ma in Jurassic sandstones of the Graben axis. A link between overpressure-controlled fluid flow and the K-Ar dates of authigenic illite in the Jurassic sandstones is delineated. Measured illite dates coincide with modelled periods of declining fluid flow. A link to the incursion of organic acids from adjacent mudstones into the sandstones is proposed, with the supply of organic acids controlled by the compaction and overpressure in the basin. The distribution of porosity within Jurassic sandstones is examined and is shown to be controlled by the complex distribution of overpressure. Overpressure supports the development of secondary porosity. Products of mineral dissolution are preferentially removed from Leak Points due to enhanced vertical fluid flow. This results in 10-12% excess porosity at 4.6 km depth. Overpressure is a dynamic system, with basin-scale structures such as pressure cells being caused by microscopic changes in pore size. The basin-scale overpressure systems in turn effect pore-scale alterations on the basin. Overpressure is an expression of the complex dynamic interaction of coupled hydrogeological and geochemical processes active throughout the evolution of the basin

Crude Oil Exploration in the World

"Crude Oil Exploration in the World" contains multidisciplinary chapters in the fields of prospection and exploration of crude oils all over the world in addition to environmental impact assessments, oil spills and marketing of crude oils

Tracing back the source of contamination

From the time a contaminant is detected in an observation well, the question of where and when the contaminant was introduced in the aquifer needs an answer. Many techniques have been proposed to answer this question, but virtually all of them assume that the aquifer and its dynamics are perfectly known. This work discusses a new approach for the simultaneous identification of the contaminant source location and the spatial variability of hydraulic conductivity in an aquifer which has been validated on synthetic and laboratory experiments and which is in the process of being validated on a real aquifer

Earth Resources: A continuing bibliography with indexes, issue 10, August 1976

This bibliography lists 506 reports, articles, and other documents introduced into the NASA scientific and technical information system between April 1976 and June 1976. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis

IT\u27S NOT RAINBOWS AND UNICORNS : REGULATED COMMODITY AND WASTE PRODUCTION IN THE ALBERTA OILSANDS

This dissertation examines the regulated oilsands mining industry of Alberta, Canada, widely considered the world’s largest surface mining project. The industrial processes of oilsands mining produce well over one million barrels of petroleum commodities daily, plus even larger quantities of airborne and semisolid waste. The project argues for a critical account of production concretized in the co-constitutional relations of obdurate materiality and labor activity within a framework of regulated petro-capitalism. This pursuit requires multiple methods that combine archives, participant observation, and semi-structured interviews to understand workers’ shift-to-shift relations inside the “black box” of regulated oilsands mining production where materiality co-constitutes the processes and outcomes of resource development and waste-intensive production. Here, the central contradiction pits the industry’s colossal environmental impact and its regulated environmental relations, which – despite chronic exceedances – are held under some control by provincial and federal environmental agents, further attenuated by firms’ selective voluntary compliance with global quality standards as well as whistleblowers and otherwise “troublesome” employees. ‘It’s not rainbows and unicorns,’ explains one informant, distilling workers’ views of the safety and environmental hazards they simultaneously produce and endure as wage laborers despite pervasive regulation. In addition to buttressing geographical conceptualizations of socionatural resource production, contributions arise in the sympathetic engagement with workers, which may hold useful insights for activism against the industry’s environmental outcomes

Advances in Unconventional Oil and Gas

This book focuses on the latest progress in unconventional oil and gas (such as coalbed methane, shale gas, tight gas, heavy oil, hydrate, etc.) exploration and development, including reservoir characterization, gas origin and storage, accumulation geology, hydrocarbon generation evolution, fracturing technology, enhanced oil recovery, etc. Some new methods are proposed to improve the gas extraction in coal seams, characterize the relative permeability of reservoirs, improve the heat control effect of hydrate-bearing sediment, improve the development efficiency of heavy oil, increase fracturing effectiveness in tight reservoirs, etc

Developing a risk assessment model using fuzzy logic to assess groundwater contamination from hydraulic fracturing

Technological advances in directional drilling has led to rapid exploitation of onshore unconventional hydrocarbons using a technique known as hydraulic fracturing. This process took off initially in the US, with Canada following closely behind, but brought with it controversial debates over environmental protection, particularly in relation to groundwater contamination and well integrity failure. Prospective shale gas regions lie across areas in Europe but countries such as the UK are facing public and government turmoil surrounding their potential exploitation. This extent of energy development requires detailed risk analysis to eliminate or mitigate damage to the natural environment. Subsurface energy activities involve complex processes and uncertain data, making comprehensive, quantitative risk assessments a challenge to develop. A new, alternative methodology was applied to onshore hydraulic fracturing to assess the risk of groundwater contamination during well injection and production. The techniques used deterministic models to construct failure scenarios with respect to groundwater contamination, stochastic approaches to determine component failures of a well, and fuzzy logic to address insufficiency or complexity in data. The framework was successfully developed using available data and regulations in British Columbia (BC), Canada. Fuzzy Fault Tree Analysis (FFTA) was demonstrated as a more robust technique compared with conventional Fault Tree Analysis (FTA) and implemented successfully to quantify cement failure. A collection of known risk analysis methods such as Event Tree Analysis (ETA), Time at Risk Failure (TRF) and Mean Time To Failure (MTTF) models were successfully applied to well integrity failure during injection, with the novel addition of quantifying cement failures. An analytical model for Surface Casing Pressure (SCP) during well production highlighted data gaps on well constructions so a fuzzy logic model was built to a 93% accuracy to determine the location of cement in a well. This novel application of fuzzy logic allowed the calculation of gas flow rate into an annulus and hence the probability of well integrity failure during production using ETA. The framework quantified several risk pathways across multiple stages of a well using site-specific data, but was successfully applied to a UK case study where there existed significant differences in geology, well construction and regulations. The application required little extra work and demonstrated the success and limitations of the model and where future work could improve model development. This research indicated that risks to groundwater from hydraulic fracturing differ substantially depending on well construction. Weighing up the risk to groundwater compared with financial gain for well construction will be essential for decision-makers and policy. To reduce the social anxiety of hydraulic fracturing in the UK, decision-makers who face criticism must ensure information is disseminated properly to the public with a well-defined risk analysis which can be interpreted easily without prerequisite knowledge. Finally, although this research is based on onshore hydraulic fracturing, the risk assessment techniques are generic enough to allow application of this research to other subsurface activities such as CO2 sequestration, waste injection disposal and geothermal energy.Engineering and Physical Sciences Research Council (EPSRC