Osareni C. Ogiesoba

Porosity prediction from seismic attributes of the Ordovician Trenton-Black River groups, Rochester field, southern Ontario

This article integrates three-dimensional (3-D) seismic attributes and log data to determine porosity distribution of the Ordovician Trenton-Black River groups within the Rochester field, southern Ontario. The rocks are composed of tight limestone, parts of which were dolomitized to form porous reservoir rock. Previous studies of the Trenton-Black River dolomite reservoirs have indicated a close relationship between faulting and reservoir development, but few published studies have attempted to examine these relationships using 3-D seismic data. This study explores the stratigraphy and structure of the Rochester fault-related dolomite reservoir using 3-D seismic data and neural networks to predict porosity. By predicting porosity using seismic attributes, vertical and lateral distributions of porosity that can be used to guide development and exploration drilling for optimal hydrocarbon recovery were obtained. The sites of highest porosity were found to be along and within the fault zones. Faults extending from the basement into overlying Paleozoic rocks are composed of several short-plane, vertical, and subvertical fault segments. However, some of these faults appear to have originated and died within the Paleozoic rocks; they cannot be traced to the basement because of little or no offset where they penetrate the basement. Although the five identified attributes are considered important in exploration for fault-related dolomite reservoirs, the single most important attribute to employ is the amplitude envelope because the other attributes are mathematically related to it. Furthermore, the sags that are seen in the Rochester field are due to the combined effects of low-velocity pushdown and faulting. Methods and results presented in this study can be used to explore and develop fault-related dolomite reservoirs elsewhere in similar geologic settings.

Seismic interpretation of mass-transport deposits within the upper Oligocene Frio Formation, south Texas Gulf Coast

We integrated well logs and three-dimensional seismic data to describe a wedge of deformed shallow Frio rocks lying above a major bed-parallel decollement within the upper Oligocene Frio Formation located between the Houston and Norias deltas on the south Texas Gulf Coast. Our analyses show that the identified deformed shallow Frio rocks can be divided into proximal clay-rich and low-permeability sandstones characterized by discontinuous, mounded, and chaotic seismic events; near-proximal, clay-poor, and high-permeability sandstones characterized by parallel to subparallel bedded seismic events; and distal sand-, silt-, and mudstones composed of a mix of proximal and near-proximal rocks. All of the deformed rocks are composed of acoustic-impedance materials that are lower than those of the undeformed shallow Frio and are underlain by low-velocity, overpressured, shale-rich rocks. The mechanism that triggered the collapse of the shallow Frio and subsequent development of mass-transport deposits is attributed to an uprising, overpressured, shale-rich high and the development of a shelf-edge listric fault. Proprietary biostratigraphic data show that the collapse of the shallow Frio in areas between the Houston and Norias deltas occurred between 27.5 and 25.3 Ma—approximately the same time as the Hackberry collapse in the Mississippi delta. In the proximal area, interpreted paleowater depths from biostratigraphic data based on benthic foraminifers range from 60 to 120 ft (20–40 m) in a shallow neritic environment. In contrast, the distal area lies in paleowater depths interpreted to be between 120 and 300 ft (40–90 m) in a middle neritic environment.

Seismic multiattribute analysis for shale gas/oil within the Austin Chalk and Eagle Ford Shale in a submarine volcanic terrain, Maverick Basin, South Texas

AbstractWe conducted seismic multiattribute analysis by combining seismic data with wireline logs to determine hydrocarbon sweet spots and predict resistivity distribution (using the deep induction log) within the Austin Chalk and Eagle Ford Shale in South Texas. Our investigations found that hydrocarbon sweet spots are characterized by high resistivity, high total organic carbon (TOC), high acoustic impedance (i.e., high brittleness), and low bulk volume water (BVW), suggesting that a combination of these log properties is required to identify sweet spots. Although the lower Austin Chalk and upper and lower Eagle Ford Shale intervals constitute hydrocarbon-sweet-spot zones, resistivity values and TOC concentrations are not evenly distributed; thus, the rock intervals are not productive everywhere. Most productive zones within the lower Austin Chalk are associated with Eagle Ford Shale vertical-subvertical en echelon faults, suggesting hydrocarbon migration from the Eagle Ford Shale. Although the quality ...

Diffraction imaging of polygonal faults within a submarine volcanic terrain, Maverick Basin, south Texas

AbstractPolygonal fault systems are common structural features of intracratonic continental margins. The map-view geometry of these faults became apparent with the use of powerful fault-imaging seismic attributes, such as coherence and curvature. However, these attributes lack the amplitude information necessary for lithological evaluation. We developed a 3D diffraction volume that not only imaged faults but also contained amplitude information. From the unmigrated stack volume, we extracted diffractions that were transformed into amplitude envelope and root-mean-square amplitude volumes. These attributes, together with clay volume (Vclay) data, were extracted along interpreted horizons and fault planes. Crossplots between seismic attributes and Vclay enabled linear relationships between the attributes and Vclay, which were used to infer lithological composition within fault zones. Our results found that, although the fault zones were clay filled, some subvertically inclined clay-poor zones that could ser...

Fault imaging in hydrothermal dolomite reservoirs: A case study

Most hydrocarbon fields found within the Ordovician Trenton and Black River Groups of the eastern United States and eastern Canada are associated with basement-related faults. These faults are best imaged by 3D seismic technology. Because of environmental conditions, seismic data often are contaminated by noise that masks fault terminations and reduces signal-to-noise ratio. As a result, seismic horizons are discontinuous, calculated coherence values are affected adversely, and horizon interpretation and fault identification are difficult, if not impossible. Poststack processing is required to attenuate this noise before an optimal interpreta-tion can be done. We conducted a three-step poststack processing flow to attenuate noise and highlight fault terminations. Noise-reducing algorithms consist of frequency-space (f-x) deconvolution, zero-phase filtering, and τ-p filtering. The structural grain of major faults identified with these techniques agrees with the regional strike of major faults previously de...

Correlation between seismic diffractions extracted from vertical seismic profiling data and borehole logging in a carbonate environment

AbstractSeismic diffractions may play an important role in seismic interpretation because they characterize geologic objects that might not be visible for conventional seismic attribute analysis. Diffractivity may be caused by, and consequently may define, tectonic dislocations (faults and fractures), lithologic variations, and fluid saturation within rocks. We have tied seismic diffractions extracted from vertical seismic profiling (VSP) data and borehole logging, from which we recognized the reasons that were responsible for diffractivity of the strata. First, we processed a multisource multicomponent VSP data set to extract seismic diffractions and constructed diffraction images of the strata for all three of the VSP data components. Then, we performed joint analysis of well logs and diffractions to obtain petrophysical attributes associated with diffraction images. We divided the rock succession into several units, which have different diffraction properties. We identified compacted rock, alternating ...

Application of thin-bed indicator and sweetness attribute in the evaluation of sediment composition and depositional geometry in coast-perpendicular subbasins, South Texas Gulf Coast

AbstractMy focus of study is the nature of sediments within late Eocene to middle Oligocene, coast-perpendicular subbasins located on the southwest side of the San Marcos Arch in Refugio County, near the South Texas Gulf Coast. Methods of investigation consist of 3D seismic interpretation, seismic attribute, and isochron mapping. Depositional geometry, inferred sediment composition, and bed-thickness data are examined by extraction of amplitude-envelope, sweetness, and thin-bed-indicator (TBI) attributes from the 3D seismic volume. Four subbasins, numbered SB1 through SB4 from northeast to southwest, are recognized. Although the coast-perpendicular subbasins formed at the same time and by the same processes, the sediment distribution, basin-fill history, and tectonics differ from subbasin to subbasin within the Jackson, Vicksburg, and Frio Formations. Amplitude envelopes extracted at base Jackson and at near-base Vicksburg Formation show that, although the distribution pattern of interpreted sandstone-pro...

Qualities of a good reviewer

Interpretation shares commonalities with Geophysics and the AAPG Bulletin in that it is a peer-reviewed journal. Unlike Geophysics and the AAPG Bulletin , Interpretation is built around special sections headed by a team of special-section editors who are either experts or particularly interested in

Diapiric shale and coast-perpendicular, fault-related subbasins, south Texas Gulf Coast

AbstractCoast-perpendicular shale ridges are rare structural features worldwide, and their origin remains a subject of debate. We studied some coast-perpendicular shale ridges and faults within a minibasin located onshore in Refugio County in the Texas Gulf Coast. We used 3D seismic data, visualization tools, and seismic attributes to examine the geometry of coast-perpendicular diapiric structures associated subbasins (SBs) and faults, and coast-parallel listric faults. Our results indicated that the minibasin is subdivided into four SBs by five diapiric shale ridges that intrude through the fault heaves of down-to-the-basin (synthetic) and coast-perpendicular faults. Three of the SBs are oriented perpendicular to the coast, whereas the fourth has a curvilinear form trending northeast–southwest–southeast. Of the five diapiric shale ridges, three are coast-perpendicular. The other two are curvilinear to the coast. All five diapiric shale ridges are associated with coast-perpendicular faults that bound the ...

Vp/Vs from multicomponent seismic data and automatic PS to PP time mapping

We find that post-critical angle reflected events cause errors and should not be used in the velocity analysis. The accuracy of the technique increases by decreasing the sampling interval in each variable used in the computation of semblance. This however, linearly increases the computational cost. By converting the 0 γ and the PS zerooffset times to the corresponding P-wave times, the correlation of P-wave and PS stacked sections can be implemented automatically. Correlation of the transformed synthetic data (PS to PP time using the estimated / p s V V ) is found to be good (the difference being less than 5%).