50 research outputs found
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Geologic Evaluation of Critical Production Parameters for Coalbed Methane Resources, Black Warrior Basin - Final Report
Characterization of coalbed methane occurrence and producibility in the Black Warrior basin of Alabama indicates that geologic factors are the principal controls on the occurrence and producibility of coalbed methane. Results of engineering analysis indicate that application of completion and stimulation techniques may be used to increase recovery once favorable well sites are chosen. Sedimentologic and coal-quality parameters may be used to locate regions for coalbed methane development by characterizing the occurrence, rank, and grade of coal resources. However, high-productivity trends within those regions are localized, and geologic data suggest that productivity trends may be predictable on the basis of structural and hydrologic parameters.
Several highly productive trends occur along northeast-oriented lineaments. These trends evidently are the surface expression of zones of enhanced permeability which apparently are related to fractures. Productive trends also are associated with areas of low reservoir pressure, and salinity maps indicate that fresh water has migrated toward these areas from the southeast margin of the basin. The available data indicate that structure and hydrology are critical production parameters that may be used to identify favorable well sites within regions containing significant, high-quality coal resources.Bureau of Economic Geolog
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Geologic Evaluation of Critical Production Parameters for Coalbed Methane Resources, Part II, Black Warrior Basin
Geologic evaluation of critical production parameters for coalbed-methane resources in the Black Warrior basin of Alabama employed an interdisciplinary approach that utilized structural, coal-quality, sedimentologic, hydrologic, and engineering data. Results indicate that geologic factors are a major control on the producibility of coalbed methane and that completion techniques may be used to increase recovery if tailored to specific geologic settings. Sedimentologic and coal-quality parameters may be used to locate regions for coalbed methane development by characterizing the occurrence, rank, and grade of coal resources. However, high-productivity trends within those regions are localized, and geologic data suggest that productivity trends may be predictable. Several highly productive trends occur along northeast-oriented lineaments. These lineaments are the inferred surface expression of zones of enhanced permeability which are related to fractures. Productive trends also are associated with areas of low reservoir pressure, and salinity maps indicate that fresh water has migrated toward areas with low reservoir pressure. The available data indicate that structure and hydrology are critical production parameters that may be used to identify favorable well sites within regions containing significant coalbed-methane resources.Bureau of Economic Geolog
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Area balance and strain in an extensional fault system: Strategies for improved oil recovery in fractured chalk, Gilbertown Field, southwestern Alabama. Annual report, March 1996--March 1997
Gilbertown Field is the oldest oil field in Alabama and produces oil from chalk of the Upper Cretaceous Selma Group and from sandstone of the Eutaw Formation along the southern margin of the Gilbertown fault system. Most of the field has been in primary recovery since establishment, but production has declined to marginally economic levels. This investigation applies advanced geologic concepts designed to aid implementation of improved recovery programs. The Gilbertown fault system is detached at the base of Jurassic salt. The fault system began forming as a half graben and evolved in to a full graben by the Late Cretaceous. Conventional trapping mechanisms are effective in Eutaw sandstone, whereas oil in Selma chalk is trapped in faults and fault-related fractures. Burial modeling establishes that the subsidence history of the Gilbertown area is typical of extensional basins and includes a major component of sediment loading and compaction. Surface mapping and fracture analysis indicate that faults offset strata as young as Miocene and that joints may be related to regional uplift postdating fault movement. Preliminary balanced structural models of the Gilbertown fault system indicate that synsedimentary growth factors need to be incorporated into the basic equations of area balance to model strain and predict fractures in Selma and Eutaw reservoirs
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GEOLOGIC SCREENING CRITERIA FOR SEQUESTRATION OF CO2 IN COAL: QUANTIFYING POTENTIAL OF THE BLACK WARRIOR COALBED METHANE FAIRWAY, ALABAMA
Sequestration of CO{sub 2} in coal has potential to reduce greenhouse gas emissions from coal-fired power plants while enhancing coalbed methane recovery. Data from more than 4,000 coalbed methane wells in the Black Warrior basin of Alabama provide an opportunity to quantify the carbon sequestration potential of coal and to develop a geologic screening model for the application of carbon sequestration technology. This report summarizes stratigraphy and sedimentation, structural geology, geothermics, hydrology, coal quality, gas capacity, and production characteristics of coal in the Black Warrior coalbed methane fairway and the implications of geology for carbon sequestration and enhanced coalbed methane recovery. Coal in the Black Warrior basin is distributed among several fluvial-deltaic coal zones in the Lower Pennsylvanian Pottsville Formation. Most coal zones contain one to three coal beds that are significant targets for coalbed methane production and carbon sequestration, and net coal thickness generally increases southeastward. Pottsville strata have effectively no matrix permeability to water, so virtually all flow is through natural fractures. Faults and folds influence the abundance and openness of fractures and, hence, the performance of coalbed methane wells. Water chemistry in the Pottsville Formation ranges from fresh to saline, and zones with TDS content lower than 10,000 mg/L can be classified as USDW. An aquifer exemption facilitating enhanced recovery in USDW can be obtained where TDS content is higher than 3,000 mg/L. Carbon dioxide becomes a supercritical fluid above a temperature of 88 F and a pressure of 1,074 psi. Reservoir temperature exceeds 88 F in much of the study area. Hydrostatic pressure gradients range from normal to extremely underpressured. A large area of underpressure is developed around closely spaced longwall coal mines, and areas of natural underpressure are distributed among the coalbed methane fields. The mobility and reactivity of supercritical CO{sub 2} in coal-bearing strata is unknown, and potential exists for supercritical conditions to develop below a depth of 2,480 feet following abandonment of the coalbed methane fields. High-pressure adsorption isotherms confirm that coal sorbs approximately twice as much CO{sub 2} as CH{sub 4} and approximately four times as much CO{sub 2} as N{sub 2}. Analysis of isotherm data reveals that the sorption performance of each gas can vary by a factor of two depending on rank and ash content. Gas content data exhibit extreme vertical and lateral variability that is the product of a complex burial history involving an early phase of thermogenic gas generation and an ongoing stage of late biogenic gas generation. Production characteristics of coalbed methane wells are helpful for identifying areas that are candidates for carbon sequestration and enhanced coalbed methane recovery. Many geologic and engineering factors, including well construction, well spacing, and regional structure influence well performance. Close fault spacing limits areas where five-spot patterns may be developed for enhanced gas recovery, but large structural panels lacking normal faults are in several gas fields and can be given priority as areas to demonstrate and commercialize carbon sequestration technology in coalbed methane reservoirs
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Area balance and strain in an extensional fault system: Strategies for improved oil recovery in fractured chalk, Gilbertown Field, southwestern Alabama. Final report, March 1996--September 1998
This project was designed to analyze the structure of Mesozoic and Tertiary strata in Gilbertown Field and adjacent areas to suggest ways in which oil recovery can be improved. The Eutaw Formation comprises 7 major flow units and is dominated by low-resistivity, low-contrast play that is difficult to characterize quantitatively. Selma chalk produces strictly from fault-related fractures that were mineralized as warm fluid migrated from deep sources. Resistivity, dipmeter, and fracture identification logs corroborate that deformation is concentrated in the hanging-wall drag zones. New area balancing techniques were developed to characterize growth strata and confirm that strain is concentrated in hanging-wall drag zones. Curvature analysis indicates that the faults contain numerous fault bends that influence fracture distribution. Eutaw oil is produced strictly from footwall uplifts, whereas Selma oil is produced from fault-related fractures. Clay smear and mineralization may be significant trapping mechanisms in the Eutaw Formation. The critical seal for Selma reservoirs, by contrast, is where Tertiary clay in the hanging wall is juxtaposed with poorly fractured Selma chalk in the footwall. Gilbertown Field can be revitalized by infill drilling and recompletion of existing wells. Directional drilling may be a viable technique for recovering untapped oil from Selma chalk. Revitalization is now underway, and the first new production wells since 1985 are being drilled in the western part of the field
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Structure, Sedimentology, Coal Quality and Hydrology of the Black Warrior Basin in Alabama: Controls on the Occurrence and Produciliblity of Coalbed Methane
Geologic evaluation of critical production parameters in the Black Warrior basin employed an interdisciplinary approach that utilized structural, sedimentologic, coal-quality, hydrologic, completion, and production data. Results indicate that geologic structure affected sedimentation, coalification, hydrogeology, and the ultimate occurrence and producibility of coalbed methane. Geologic trend analysis was used to characterize regional coalbed-methane potential, and results indicate that many parts of the basin have untapped resources. Some highly productive trends coincide with northeast-trending structures that apparently are zones of enhanced fracture permeability. Water-production data indicate that many high-permeability trends exist that are not associated with exceptional coalbed-methane production and that the coal beds are structurally compartmentalized reservoirs. Water-level data indicate that all highly productive coalbed-methane wells occur where reservoir pressure has been lowered significantly. Therefore, highly productive areas apparently represent structural compartments where formation pressure has been lowered enough to facilitate desorption of a large quantity of methane. Results of this research suggest that completion technology and field design can be tailored to specific geologic settings to produce from reservoir compartments that are readily depressurized, thereby optimizing reservoir drainage.Bureau of Economic Geolog
Temporal fine structure of nightime spike events in auroral radio absorption, studied by wavelet method
The auroral absorption spike event, occurring generally at the onset of a substorm, is distinguished by its high intensity and short duration. This paper reports the presence of a fine structure within the spike event. Analysis of selected examples using the Morlet wavelet shows that within the 1 – 2 min duration of the spike are significant modulations with periodicities in the bands 15 – 60 s (67 – 16 mHz), and 5 – 10 s (200 – 100 mHz), the former being the stronger. The slower fluctuations can amount to more than 10% of the absorption, and they were observed in every example (seven out of nine) in which the spike was moving poleward. They were absent in the other two cases, when the spike moved equatorward. In the examples studied, the 15 – 60 s absorption pulsations were accompanied by magnetic micropulsations of impulsive type (Pi) having a periodity that was similar or harmonically related. The connection is only close while the spike event is moving. Consideration of the details suggests that both the magnetic and the absorption pulsations are related to the acceleration process at substorm onset, the flux of energetic particles into the auroral zone producing the radio absorption being modulated with, though not by, the geomagnetic field variations. The 5 – 10 s pulsations, which are considerably weaker, appeared in both the absorption and the magnetic records, but in this case with no obvious connection between them
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Area balance and strain in an extensional fault system: Strategies for improved oil recovery in fractured chalk, Gilbertown Field, southwestern Alabama -- Year 2. Annual report, March 1997--March 1998
Gilbertown Field is the oldest oil field in Alabama and has produced oil from fractured chalk of the Cretaceous Selma Group and glauconitic sandstone of the Eutaw Formation. Nearly all of Gilbertown Field is still in primary recovery, although waterflooding has been attempted locally. The objective of this project is to analyze the geologic structure and burial history of Mesozoic and Tertiary strata in Gilbertown Field and adjacent areas in order to suggest ways in which oil recovery can be improved. Indeed, the decline of oil production to marginally economic levels in recent years has made this type of analysis timely and practical. Key technical advancements being sought include understanding the relationship of requisite strain to production in Gilbertown reservoirs, incorporation of synsedimentary growth factors into models of area balance, quantification of the relationship between requisite strain and bed curvature, determination of the timing of hydrocarbon generation, and identification of the avenues and mechanisms of fluid transport