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This dissertation focuses on interpreting the spatial variations of seismic amplitude data as a function of rock properties for the Haynesville Shale. To achieve this goal, I investigate the relationships between the rock properties and elastic properties, and calibrate rock-physics models by constraining both P- and S-wave velocities from well log data. I build a workflow to estimate the rock properties along with uncertainties from the P- and S-wave information. I correlate the estimated rock properties with the seismic amplitude data quantitatively. The rock properties, such as porosity, pore shape and composition, provide very useful information in determining locations with relatively high porosities and large fractions of brittle components favorable for hydraulic fracturing. Here the brittle components will have the fractures remain opened for longer time than the other components. Porosity helps to determine gas capacity and the estimated ultimate recovery (EUR); composition contributes to understand the brittle/ductile strength of shales, and pore shape provides additional information to determine the brittle/ductile strength of the shale. I use effective medium models to constrain P- and S-wave information. The rock-physics model includes an isotropic and an anisotropic effective medium model. The isotropic effective medium model provides a porous rock matrix with multiple mineral phases and pores with different aspect ratios. The anisotropic effective medium model provides frequency- and pore-pressure-dependent anisotropy. I estimate the rock properties with uncertainties using grid searching, conditioned by the calibrated rock-physics models. At well locations, I use the sonic log as input in the rock-physics models. At areas away from the well locations, I use the prestack seismic inverted P- and S-impedances as input in the rock-physics models. The estimated rock properties are correlated with the seismic amplitude data and help to interpret the spatial variations observed from seismic data. I check the accuracy of the estimated rock properties by comparing the elastic properties from seismic inversion and the ones derived from estimated rock properties. Furthermore, I link the estimated rock properties to the microstructure images and interpret the modeling results using observations from microstructure images. The characterization contributes to understand what causes the seismic amplitude variations for the Haynesville Shale. The same seismic reservoir characterization procedure could be applied to other unconventional gas shales.
This thesis investigates the relationship between elastic properties and rock properties of the Haynesville Shale using rock physics modeling, simultaneous seismic inversion, and grid searching. A workflow is developed in which a rock physics model is built and calibrated to well data in the Haynesville Shale and then applied to 3D seismic inversion data to predict porosity and mineralogy away from the borehole locations. The rock physics model describes the relationship between porosity, mineral composition, pore shape, and elastic stiffness using the anisotropic differential effective medium model. The calibrated rock physics model is used to generate a modeling space representing a range of mineral compositions and porosities with a calibrated mean pore shape. The model space is grid searched using objective functions to select a range of models that describe the inverted P-impedance, S-impedance, and density volumes. The selected models provide a range of possible rock properties (porosity and mineral composition) and an estimate of uncertainty. The mineral properties were mapped in three dimensions within the area of interest using this modeling technique and inversion workflow. This map of mineral content and porosity can be interpreted to predict the best areas for hydraulic fracturing.
In unconventional resources such as the Haynesville Shale, a proper understanding of natural fracture patterns is essential to enhancing the economic success of petroleum extraction. The spatial density of naturally occurring fracture sets affects drainage area and optimal drilling location(s), and the azimuth of the strike of the predominant fracture set affects the ideal orientation of wells. In the absence of data to directly determine these fracture characteristics, such as Formation Microimaging (FMI) logs, these natural fracture patterns can be analyzed by examining the seismic anisotropy present in the reservoir. Anisotropy introduced from aligned fracture sets creates predictable azimuthal variations in the seismic wavefield. This allows the reservoir anisotropy, and thus the fracturing present in the reservoir, to be studied indirectly through the azimuthal analysis of industry standard 3D seismic data. The work presented here outlines three distinct methodologies, which utilize azimuthal amplitude variations (AVAZ) present in 3D seismic data, to infer fracture characteristics without the need for substantial well log information. Two of these methods have been previously established and assume the reservoir to be characteristic of Horizontally Transverse Isotropic (HTI). The last method is novel and assumes orthorhombic anisotropy when inverting for fracture density and is able to unambiguously invert for fracture azimuth. All methodologies used in this work produced similar results, increasing confidence in the accuracy of these results through statistical repeatability. Fracture density inversion results indicate spatially varying fracture density throughout the area, with a distinct area of higher fracture density present in the Northwestern corner of the area analyzed. Spatially varying fracture density and localized pockets of fracturing is consistent with expectation from analyzing production data and FMI logs from other areas of the Haynesville. Fracture azimuth inversion results showed some variability; however, the novel method presented in this thesis indicates that the azimuth of the predominant fracture set is oriented at a compass bearing of approximately 82 degrees -- rotated slightly counterclockwise from an east-west orientation. Fracture azimuth results agree well with expectations from a regional stress analysis and from examining comparable formations with known fracture patterns in the surrounding area.
Provides comprehensive information about the key exploration, development and optimization concepts required for gas shale reservoirs Includes statistics about gas shale resources and countries that have shale gas potential Addresses the challenges that oil and gas industries may confront for gas shale reservoir exploration and development Introduces petrophysical analysis, rock physics, geomechanics and passive seismic methods for gas shale plays Details shale gas environmental issues and challenges, economic consideration for gas shale reservoirs Includes case studies of major producing gas shale formations
There are many tools and techniques for characterizing oil and gas reservoirs. Seismic-reflection techniques include conventional 2D and 3D seismic, 4D time-lapse seismic, multicomponent seismic, crosswell seismic, seismic inversion, and seismic attribute analysis, all designed to enhance stratigraphy/structure detection, resolution, and characterization. These techniques are constantly being improved. Drilling and coring a well provides the “ground truth” for seismic interpretation. Rock formations are directly sampled by cuttings and by core and indirectly characterized with a variety of conventional and specialized well logs. To maximize characterization and optimize production, many of these tools as possible should be employed. It is often less expensive to utilize a wide variety of tools that directly image or measure reservoir properties at different scales than to drill one or two dry holes.
In recent years, the Haynesville shale has become a target for natural gas exploitation, especially with the advent of horizontal drilling and hydraulicfracturing. Located in East Texas and Northwest Louisiana, it is believed to be one of the largest producing natural gas plays in the U.S., with estimated recoverable reserves of around 75 TCF according to the Energy Information Administration (EIA, 2011). Current total daily production for the entire play is around 5.4 Bcf/d. The economic potential of the Haynesville shale gas play is propelled by recent gradual rebounds in natural gas prices, increased industrial utilization of gas, and expansion of LNG export terminals along the gulf coast due to the lifting of the decades-old ban on exporting petroleum products. Consequently, it is imperative to properly evaluate the petrophysical attributes of the shale in order to understand the reservoir characteristics that may ultimately influence production. This study focused on the petrophysical evaluation of wells in East Texas and Northwest Louisiana. Wireline logs and core data were integrated to provide a predictive template for targeting and landing lateral wellbores within the shale in order to provide useful insight for hydraulic fracture stimulation with the view of optimizing production. The critical factors determined to influence the target zones include geomechanical properties such as brittleness, and geochemical properties such as the mineral volumes in the rock. These were calculated from logs using equations previously published in literature and correlated to nearby core measurements for verification. Already drilled and completed laterals were also evaluated to identify potential refracturing opportunities that could remedy production decline. The stimulation techniques and production outcomes of these laterals were examined in an attempt to identify possible trends and contrasts accordingly. The results show that the geomechanical properties vary across the shale play area. The geomechanical and geochemical properties can be useful in target selection for landing horizontal wells and effective fracture treatments, but they cannot by themselves guarantee productivity as other factors have to be taken into consideration such as completions method. The various operational constraints and development patterns such as different lateral lengths and age/style of completions make it difficult to do effective well-to-well production comparison; however the results points to trends such as longer lateral lengths with greater fracture stages to boost production. Additionally, in some areas, it has been established via the petrophysical analysis that there may be additional intervals in which to land a second horizontal well. This will surely lead to better exploitation and increased production from the reservoir.
Practical Solutions to Integrated Oil and Gas Reservoir Analysis: Geophysical and Geological Perspectives is a well-timed source of information addressing the growing integration of geophysical, geological, reservoir engineering, production, and petrophysical data in predicting and determining reservoir properties. These include reservoir extent and sand development away from the well bore, characterizations of undrilled prospects, and optimization planning for field development. As such, geoscientists must now learn the technology, processes, and challenges involved within their specific functions in order to complete day-to-day activities. A broad collection of real-life problems and challenging questions encountered by geoscientists in the exploration and development of oil and gas fields, the book treats subjects ranging from Basin Analysis, to identifying and mapping structures, stratigraphy, the distribution of fracture, and the identification of pore fluids. Looking at the well-to-seismic tie, time-to-depth conversion, AVO analysis, seismic inversion, rock physics, and pore pressure analysis/prediction, the text examines challenges encountered in these technical areas, and also includes solutions and techniques used to overcome those challenges. Presents a thorough understanding of the contributions and issues faced by the various disciplines that contribute towards characterizing a wide spectrum of reservoirs (Conventional, Shale Oil and Gas, as well as Carbonate reservoirs) Provides a much needed and integrated approach amongst disciplines including geology, geophysics, petrophysics, reservoir and drilling engineering Includes case studies on different reservoir settings from around the world including Western Canadian Sedimentary Basin, Gulf of Guinea, Gulf of Mexico, Milne point field in Alaska, North-Sea, San Jorge Basin, and Bossier and Haynesville Shales, and others to help illustrate key points