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Utility of small-angle neutron scattering to quantifying accessible and wettable pores in shale
Published on November 13, 2017
Since 2000, the technological advances of horizontal drilling and hydraulic fracturing in the United States have led to a dramatic increase in hydrocarbon (gas and oil) production from shale formations, changing the energy landscape in the US and worldwide. However, total gas recovery is only 12 to 30%, while the tight-oil recovery rate from shale formations is even lower at 5 to 10%. Dr. Hu s research group has been studying the nano-petrophysical aspects, mainly pore connectivity and wettability, which are unique to shale to lead to steep production decline and low overall production. The group uses an integrated approaches of pycnometry ((liquid and gas), pore and bulk volume measurement after vacuum saturation,, porosimetry (mercury injection capillary pressure, low-pressure gas physisorption isotherm, water vapor adsorption/desorption isotherm, nuclear magnetic resonance cyroporometry), imaging (X-ray computed tomography, Wood’s metal impregnation, field emission-scanning electron microscopy), scattering (ultra- and small-angle neutron, small angle X-ray), as well and the utility of both hydrophilic and hydrophobic fluids as well as fluid invasion tests (imbibition, diffusion, vacuum saturation) followed by laser ablation-inductively coupled plasma-mass spectrometry imaging of different nm-sized tracers. Among a total of 18 SCI papers published in 2017 from Dr. Hu s group, a recent paper of using SANS (small angle neutron scattering) to quantify accessible pore spaces of various shale is published in Scientific Report, is an online, open access journal from the publishers of Nature, with an impact factor of 4.26. The group has been continuing the work to tease out the relationship between topological connectivity, wettability and effective pore accessibility, using a contrast-matching technique with SANS.
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Late Paleozoic subsidence and burial history of the Fort Worth basin
Published on November 01, 2017
The Fort Worth basin in northcentral Texas is a major shale-gas producer, yet its subsidence history and relationship to the Ouachita fold-thrust belt have not been well understood. We studied the depositional patterns of the basin during the late Paleozoic by correlating well logs and constructing structure and isopach maps. We then modeled the one-dimensional (1-D) and two-dimensional subsidence history of the basin and constrained its relationship to the Ouachita orogen. Because the super-Middle Pennsylvanian strata were largely eroded in the region, adding uncertainty to the subsidence reconstruction, we used PetroMod 1-D to conduct thermal-maturation modeling to constrain the postMiddle Pennsylvanian burial and exhumation history by matching the modeled vitrinite reflectance with measured vitrinite reflectance along five depth profiles. Our results of depositional patterns show that the tectonic uplift of the Muenster uplift to the northeast of the basin influenced subsidence as early as the Middle Mississippian, and the Ouachita orogen became the primary tectonic load by the late Middle Pennsylvanian when the depocenter shifted to the east. Our results show that the basin experienced 3.7 -- 5.2 km (12,100 –- 17,100 ft) of burial during the Pennsylvanian, and the burial depth deepens toward the east. We attributed the causes of deep Pennsylvanian burial and its spatial variation to flexural subsidence that continued into the Late Pennsylvanian in response to the growth of the Ouachita orogen and southeastward suturing of Laurentia and Gondwana. The modeling results also suggest that the Mississippian Barnett Shale reached the gas maturation window during the Middle Late Pennsylvanian.
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In situ peridotitic diamond in Indus ophiolite sourced from hydrocarbon fluids in the mantle transition zone
Published on June 09, 2017
In recent years ophiolitic diamonds have been reported mostly from podiform chromitites. However, the mechanism of such diamond formation remains unknown. We report in situ diamond, graphite pseudomorphs after diamond crystals, and hydrocarbon (C-H) and hydrogen (H2) fluid inclusions in ultrahigh-pressure (UHP) peridotitic minerals of the Nidar ophiolite, Indus suture zone. Diamond occurs as octahedral inclusion along with nitrogen (N2) in orthoenstatite. Methane (CH4) also occurs with UHP clinoenstatite (>8 GPa) in orthoenstatite. The graphite pseudomorphs after diamond crystals and primary hydrocarbon (C-H), and hydrogen (H2) fluids are included in olivine. Oriented hematite (?-Fe2O3) exsolutions are also present in the olivines, indicating a precursory ?-Mg2SiO4 phase of the host olivines. This assemblage of diamond, graphite, C-H and H2 has not previously been reported from any ophiolitic peridotite. The hydrocarbon fluids in UHP clinoenstatites and retrogressed ?-Mg2SiO4 strongly suggest their source from the mantle transition zone or base of the upper mantle. We conclude that the peridotitic diamonds precipitated from C-H fluids during mantle upwelling beneath the Neo-Tethys Ocean spreading center.
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Identifying globally synchronous Permian Triassic boundary levels in successions in China and Vietnam using Graphic Correlation
Published on March 30, 2017
Understanding the timing and correlation of significant global events in Earth history is facilitated by the Global Boundary Stratotype Section and Point (GSSP) concept, along with multi-proxy correlation techniques. As an example, the Permian Triassic boundary (PTB) GSSP is used herein to correlate three PTB successions in east and southeast Asia. The PTB is defined using the First Appearance Datum (FAD) of the conodont Hindeodus parvus at the Meishan D section in China. By definition then, Meishan D is the only section on Earth where the FAD of H. parvus represents the beginning of the Triassic, at ~ 251.88 Ma, and thus the end of the Permian. Therefore, when correlating strata in any other section back to the PTB using biostratigraphic data, the local Lowest Observed Occurrence Point (LOOP) of H. parvus will probably not equate precisely to the defined FAD GSSP level (the PTB) for the beginning of the Triassic at Meishan D. The Graphic Correlation method, applied to PTB sites in China and Vietnam, is used herein to demonstrate that LOOPs of H. parvus in other successions are not equivalent in time to the PTB FAD. The LOOP and Highest Observed Occurrence Point (HOOP) for conodont data at two other successions studied, Huangzhishan in China, and Lung Cam in Vietnam, are used to determine the approximate level where the Triassic begins in these successions, resulting in high-resolution correlation among the sections and correlation back to the PTB GSSP level. It is demonstrated that when critical biostratigraphic data are missing, multiple proxy correlation techniques, geochemical, geophysical and, in some regional instances, unique lithostratigraphic information such as coeval ash beds, can be used to aid in locating the boundary in successions that are not the defining GSSP. LOOP and HOOP data are used to establish a Line of Correlation to differentiate between a defining PTB H. parvus FAD versus the H. parvus LOOP in secondary successions, and to project the PTB FAD into secondary sections to define the PTB at these localities. In addition, the timing of H. parvus arrivals at these sections is used to establish rough dispersal rates and patterns in the region.
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