Three-dimensional architecture of a coalesced, collapsed-paleocave system in the Lower Ordovician Ellenburger Group, central Texas

AAPG Bulletin ◽  
2004 ◽  
Vol 88 (5) ◽  
pp. 545-564 ◽  
Author(s):  
Robert G. Loucks ◽  
Paul K. Mescher ◽  
George A. McMechan
Keyword(s):  
Three Dimensional ◽  
Lower Ordovician ◽  
Central Texas

Characterization of a coalesced, collapsed paleocave reservoir analog using GPR and well‐core data

Geophysics ◽  
2002 ◽  
Vol 67 (4) ◽  
pp. 1148-1158 ◽  
Author(s):  
George A. McMechan ◽  
Robert G. Loucks ◽  
Paul Mescher ◽  
Xiaoxian Zeng
Keyword(s):  
Host Rock ◽  
Three Dimensional ◽  
Near Surface ◽  
Lower Ordovician ◽  
Central Texas ◽  
Integrated Interpretation ◽  
Core Descriptions ◽  
Ground Penetrating ◽  
The City

The three‐dimensional architecture, spatial complexity, and pore‐type distribution are mapped in a near‐surface analog of a coalesced, collapsed paleocave system in the Lower Ordovician Ellenburger Group near the city of Marble Falls in central Texas. The surface area of the site has dimensions of about 350 × 1000 m. The data collected include about 12 km of 50‐MHz ground‐penetrating radar (GPR) data arranged in a grid of orthogonal lines, 29 cores of about 15‐m length, and detailed facies maps of an adjacent quarry face. Electrical property measurements along with detailed core descriptions were the basis of integrated interpretation of the GPR data. Three main GPR facies are defined on the basis of degree of brecciation in the corresponding cores: undisturbed host rock, disturbed host rock, and paleocave breccia. This GPR facies division defined the major paleocave trends and the distribution of porosity types, which correlate with reservoir quality. Highly brecciated zones are separated by disturbed and undisturbed host rock. The breccia bodies that outline the trend of collapsed cave passages are up to 300 m wide; the intervening intact areas between breccias are up to 200 m wide. Understanding the breccia distribution in a reservoir analog will help in defining strategies for efficient development of coalesced, collapsed paleocave reservoirs.

Jujuyaspis borealis and associated trilobites and conodonts from the Lower Ordovician of Texas and Utah

1987 ◽  
Vol 61 (1) ◽  
pp. 112-121 ◽  
Author(s):  
James H. Stitt ◽  
James F. Miller
Keyword(s):  
United States ◽  
South America ◽  
North American ◽  
The United States ◽  
International Agreement ◽  
Lower Ordovician ◽  
Central Texas ◽  
North And South America ◽  
First Time ◽  
North And South

Jujuyaspis borealis is reported from earliest Ordovician (North American usage) limestones in central Texas and western Utah, the first time this species has been recognized in the United States. Jujuyaspis is a widespread olenid trilobite that occurs near the base of the Tremadoc Series in a variety of lithologies in North and South America, Europe, and Asia. When international agreement is reached on the exact horizon at or near the base of the Tremadoc Series that is to be used as the Cambrian–Ordovician boundary, Jujuyaspis will likely prove to be a very useful taxon for recognition of the boundary interval.

Modeling 3D porosity and permeability from GPR data in the Ellenburger Dolomite, central Texas

Geophysics ◽  
2011 ◽  
Vol 76 (6) ◽  
pp. J35-J46 ◽  
Author(s):  
Hussein Harbi ◽  
George A. McMechan
Keyword(s):  
Signal To Noise Ratio ◽  
Velocity Ratio ◽  
Three Dimensional ◽  
Carbonate Reservoir ◽  
Horizontal Orientation ◽  
Air Interface ◽  
Porosity And Permeability ◽  
Central Texas ◽  
Ground Penetrating ◽  
Velocity Tomography

Three-dimensional porosity and permeability were modeled in an Ellenburger carbonate reservoir analog from 2D crosshole and 3D surface survey ground-penetrating radar (GPR) data. Two-dimensional GPR crosshole velocity tomography, 3D migration of the GPR surface data, and porosity and permeability calibration to GPR attributes results in 3D porosity and permeability predictions that provide a consistent model of the paleocave structures and facies distributions. Picking the maximum instantaneous amplitude of the direct arrival wavelet for velocity tomography reduces uncertainties caused by a low signal-to-noise ratio, uncorrelated noise, and the interference between reflections and critical refractions at the earth/air interface. The GPR velocity is anisotropic with an average vertical to horizontal velocity ratio of 0.93, which is attributed to the dominance of the relatively horizontal orientation of the maximum porosity and permeability. Porosity and permeability trends are influenced by regional northeast-southwest and northwest-southeast striking conjugate fractures associated with the Pennsylvanian Ouachita orogeny and breccia facies generated by three episodes of burial and the resulting paleocave collapses. At depths [Formula: see text] from the present surface, large brecciated dolomite and limestone blocks have low porosity and low permeability. Between a depth of [Formula: see text] and [Formula: see text] irregular fracture orientations and distributions associated with collapse breccias have a higher average porosity and permeability. A deeper zone ([Formula: see text] to [Formula: see text] in depth), has intermediate permeability and porosity. Porosity and permeability could not be calibrated in open voids. Thus, the predictions are applicable to the core-scale to which they were calibrated, but are lower bounds for the whole volume, which contains breccias, karst, and fractures that increase both porosity and permeability at larger scales.

The orbit of Pluto over a long interval of time

1966 ◽  
Vol 25 ◽  
pp. 227-229 ◽  
Author(s):  
D. Brouwer
Keyword(s):  
Periodic Orbit ◽  
Numerical Integration ◽  
Restricted Problem ◽  
Three Dimensional ◽  
The Third ◽  
Circular Restricted Problem ◽  
Resonance Relation

The paper presents a summary of the results obtained by C. J. Cohen and E. C. Hubbard, who established by numerical integration that a resonance relation exists between the orbits of Neptune and Pluto. The problem may be explored further by approximating the motion of Pluto by that of a particle with negligible mass in the three-dimensional (circular) restricted problem. The mass of Pluto and the eccentricity of Neptune's orbit are ignored in this approximation. Significant features of the problem appear to be the presence of two critical arguments and the possibility that the orbit may be related to a periodic orbit of the third kind.

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