Abstract An understanding of trap and fault seal quality is critical for assessing hydrocarbon prospectivity. To achieve this, modern analytical techniques leverage well data and conventional industry-standard 3D seismic data to evaluate the trap, and any faults displacing the reservoir and top seal intervals. Above all, geological interpretation provides the framework of trap and fault seal analyses, but can be hindered by the data resolution, quality and acquisition style of the conventional seismic data. Furthermore, limiting the analysis to only the petroleum system at depth may lead to erroneous perceptions because interpreting overburden features, such as shallow faults or gas chimneys, can provide valuable observations with respect to container performance, and can to help validate trap and fault seal predictions. A supplement to conventional 3D data are high-resolution 3D seismic (HR3D) data, which provide detailed images of the overburden geology. This study utilizes an HR3D seismic volume in the San Luis Pass area of the Texas inner shelf, where shallow fault tips and a sizeable gas chimney are interpreted over an unsuccessful hydrocarbon prospect. Static post-drill fault seal and trap analyses suggest that the primary fault displacing the structural closure could have withheld columns of gas c. 100 m high, but disagree with our HR3D seismic interpretations and dry-well analyses. From our results, we hypothesize that tertiary gas migration through fault conduits reduced the hydrocarbon column in the prospective Early Miocene reservoir, and may have resulted from continued movement along the intersecting faults. Overall, this study reinforces the importance of understanding the overburden geology and geohistory of faulted prospects, and demonstrates the utility of pre-drill HR3D acquisition when conducting trap and fault seal analyses.

Abstract A geological understanding of the way fluids flow through a reservoir is crucial when considering waterflood developments in heterogeneous reservoirs. Recent integrated production geoscience and reservoir engineering studies on the Holland Greensand oil reservoir (Aptian) of the Rotterdam Field in the West Netherlands Basin, are used to illustrate the geological controls on fluid flow through rocks deposited in a clastic inner shelf depositional setting. An integrated understanding of the subsurface has been gained through core, log and production data analysis. Analogous Early Cretaceous Upper Greensand Formation coastal exposures in SW England have been used to gauge the scale of lateral and vertical heterogeneity, and its impact on hydrocarbon and water flow paths. Argillaceous sandstones deposited at the distal margins of a subtidal sand-sheet provide internal reservoir baffles, while fluids are believed to preferentially follow flow paths through associated laterally extensive tempestites. Cemented layers observable in wells are interpreted to be laterally restricted and are not considered as major baffles. These observations have been used to steer static reservoir model construction and subsequent simulation. Results from field testing by production logging tool analysis support the geological concepts developed and the modelling approach used. This work has important implications for defining the approach for future reservoir management and redevelopment in the Rotterdam Field, in particular the well type and configuration and completion strategies post-reservoir flooding. The application of methodologies employed in this study is recommended for similar waterflood developments.

Abstract For the last several decades, gold exploration in Nevada has been strongly focused on sedimentary rock-hosted gold deposits in the Carlin, Cortez, Independence, and Getchell trends in north-central Nevada. Accordingly, less exploration activity has been directed toward the search for similar gold deposits in the eastern Great Basin, south and east of the major trends. Deposits in the central and northern Carlin and Cortez trends are hosted primarily in Upper Devonian middle slope soft-sediment slumps and slides and base-of-slope carbonate debris flows, turbidites, and enclosing in situ fractured lime mudstones. This is in marked contrast to gold deposits in the eastern Great Basin that are hosted primarily in three chronostratigraphic horizons: (1) shallow-water, Cambrian and Ordovician carbonate platform interior, supratidal karsted horizons and shelf lagoon strata, associated with eustatic sea-level lowstands and superjacent, transgressive calcareous shale and siltstone horizons that are deposited as sea level begins to rise, (2) Early Mississippian foreland basin turbidites and debris flows overlying karsted Late Devonian platform strata, and (3) Pennsylvanian and Permian shallow marine basin strata. Stratigraphic architecture in these three horizons was influenced in part by Mesozoic (Elko and Sevier) contractional deformation, including low-angle thrust and attenuation faults, boudinage, and large-scale folds, which in turn affected the orientation and localization of synmineral brittle normal faults. A compilation of past production, reserves, and resources (including historic and inferred) suggests an overall endowment of over 41 Moz of gold (1,275 tonnes) discovered to date in the eastern Great Basin, some in relatively large deposits. Significant clusters of deposits include the Rain-Emigrant-Railroad and Bald Mountain-Alligator Ridge areas on the southern extension of the Carlin trend, the Ruby Hill-Windfall-South Lookout-Pan on the southern extension of the Cortez trend, and the Long Canyon-West Pequop-Kinsley Mountain area near Wells, Nevada. Sedimentary rock-hosted gold deposits extend to the eastern edge of the Great Basin in Utah and Idaho and include the past-producing Black Pine, Barney’s Canyon, Mercur, and Goldstrike mines. The recognition of widespread, favorable host rocks and depositional environments on the Paleozoic platform-interior shelf in the eastern Great Basin opens up vast areas that have been relatively underexplored in the past. A basic premise throughout this paper is that the better we understand the origin of rocks and the depositional and postdepositional processes under which they formed, the more accurately we can make well-founded stratigraphic, sedimentological, structural, geochemical, and diagenetic interpretations. Without this understanding, as well as the rigorous application of multiple working hypotheses to explain our observations, the advance of science and the discovery of gold deposits is problematic.

We interpret seismic-reflection profiles to determine the location and offset mode of Quaternary offshore faults beneath the Gulf of Santa Catalina in the inner California Continental Borderland. These faults are primarily northwest-trending, right-lateral, strike-slip faults, and are in the offshore Rose Canyon–Newport-Inglewood, Coronado Bank, Palos Verdes, and San Diego Trough fault zones. In addition we describe a suite of faults imaged at the base of the continental slope between Dana Point and Del Mar, California. Our new interpretations are based on high-resolution, multichannel seismic (MCS), as well as very high resolution Huntec and GeoPulse seismic-reflection profiles collected by the U.S. Geological Survey from 1998 to 2000 and MCS data collected by WesternGeco in 1975 and 1981, which have recently been made publicly available. Between La Jolla and Newport Beach, California, the Rose Canyon and Newport-Inglewood fault zones are multistranded and generally underlie the shelf break. The Rose Canyon fault zone has a more northerly strike; a left bend in the fault zone is required to connect with the Newport-Inglewood fault zone. A prominent active anticline at mid-slope depths (300–400 m) is imaged seaward of where the Rose Canyon fault zone merges with the Newport-Inglewood fault zone. The Coronado Bank fault zone is a steeply dipping, northwest-trending zone consisting of multiple strands that are imaged from south of the U.S.–Mexico border to offshore of San Mateo Point. South of the La Jolla fan valley, the Coronado Bank fault zone is primarily transtensional; this section of the fault zone ends at the La Jolla fan valley in a series of horsetail splays. The northern section of the Coronado Bank fault zone is less well developed. North of the La Jolla fan valley, the Coronado Bank fault zone forms a positive flower structure that can be mapped at least as far north as Oceanside, a distance of ~35 km. However, north of Oceanside, the Coronado Bank fault zone is more discontinuous and in places has no strong physiographic expression. The San Diego Trough fault zone consists of one or two well-defined linear fault strands that cut through the center of the San Diego Trough and strike N30°W. North of the La Jolla fan valley, this fault zone steps to the west and is composed of up to four fault strands. At the base of the continental slope, faults that show recency of movement include the San Onofre fault and reverse, oblique-slip faulting associated with the San Mateo and Carlsbad faults. In addition, the low-angle Oceanside detachment fault is imaged beneath much of the continental slope, although reflectors associated with the detachment are more prominent in the area directly offshore of San Mateo Point. North of San Mateo Point, the Oceanside fault is imaged as a northeast-dipping detachment surface with prominent folds deforming hanging-wall strata. South of San Mateo point, reflectors associated with the Oceanside detachment are often discontinuous with variable dip as imaged in WesternGeco MCS data. Recent motion along the Oceanside detachment as a reactivated thrust fault appears to be limited primarily to the area between Dana and San Mateo Points. Farther south, offshore of Carlsbad, an additional area of folding associated with the Carlsbad fault also is imaged near the base of the slope. These folds coincide with the intersection of a narrow subsurface ridge that trends at a high angle to and intersects the base of the continental slope. The complex pattern of faulting observed along the base of the continental slope associated with the San Mateo, San Onofre, and Carlsbad fault zones may be the result of block rotation. We propose that the clockwise rotation of a small crustal block between the Newport-Inglewood–Rose Canyon and Coronado Bank fault zones accounts for the localized enhanced folding along the Gulf of Santa Catalina margin. Prominent subsurface basement ridges imaged offshore of Dana Point may inhibit along-strike block translation, and thus promote block rotation.