Robert T. Ryder

The use of vertical seismic profiles in seismic investigations of the earth

During the past 8 years, the U.S. Geological Survey has conducted an extensive investigation on the use of vertical seismic profiles (VSP) in a variety of seismic exploration applications. Seismic sources used were surface air guns, vibrators, explosives, marine air guns, and downhole air guns. Source offsets have ranged from 100 to 7800 ft. Well depths have been from 1200 to over 10,000 ft. We have found three specific ways in which VSPs can be applied to seismic exploration. First, seismic events observed at the surface of the ground can be traced, level by level, to their point of origin within the earth. Thus, one can tie a surface profile to a well log with an extraordinarily high degree of confidence. Second, one can establish the detectability of a target horizon, such as a porous zone. One can determine (either before or after surface profiling) whether or not a given horizon or layered sequence returns a detectable reflection to the surface. The amplitude and character of the reflection can also ...

Black Shale Source Rocks and Oil Generation in the Cambrian and Ordovician of the Central Appalachian Basin, USA

Nearly 600 million bbl of oil (MMBO) and 1 to 1.5 trillion ft3 (tcf) of gas have been produced from Cambrian and Ordovician reservoirs (carbonate and sandstone) in the Ohio part of the Appalachian basin and on adjoining arches in Ohio, Indiana, and Ontario, Canada. Most of the oil and gas is concentrated in the giant Lima-Indiana field on the Findlay and Kankakee arches and in small fields distributed along the Knox unconformity. Based on new geochemical analyses of oils, potential source rocks, bitumen extracts, and previously published geochemical data, we conclude that the oils in both groups of fields originated from Middle and Upper Ordovician black shale (Utica and Antes shales) in the Appalachian basin. Moreover, we suggest that approximately 300 MMBO and many trillions of cubic feet of gas in the Lower Silurian Clinton sands of eastern Ohio originated in these same source rocks. Oils from the Cambrian and Ordovician reservoirs have similar saturated hydrocarbon compositions, biomarker distributions, and carbon isotope signatures. Regional variations in the oils are attributed to differences in thermal maturation rather than to differences in source. Total organic carbon content, genetic potential, regional extent, and bitumen extract geochemistry identify the black shale of the Utica and Antes shales as the most plausible source of the oils. Other Cambrian and Ordovician shale and carbonate units, such as the Wells Creek formation, which rests on the Knox unconformity, and the Rome Formation and Conasauga Group in the Rome trough, are considered to be only local petroleum sources. Tmax, CAI, and pyrolysis yields from drill-hole cuttings and core indicate that the Utica Shale in eastern and central Ohio is mature with respect to oil generation. Burial, thermal, and hydrocarbon-generation history models suggest that much of the oil was generated from the Utica-Antes source in the late Paleozoic during the Alleghanian orogeny. A pervasive fracture network controlled by basement tectonics aided in the distribution of oil from the source to the trap. This fracture network permitted oil to move laterally and stratigraphically downsection through eastward-dipping, impermeable carbonate sequences to carrier zones such as the Middle Ordovician Knox unconformity, and to reservoirs such as porous dolomite in the Middle Ordovician Trenton Limestone in the Lima-Indiana field. Some of the oil and gas from the Utica-Antes source escaped vertically through a partially fractured, leaky Upper Ordovician shale seal into widespread Lower Silurian sandstone reservoirs.

Palynology and Age of Beaverhead Formation and Their Paleotectonic Implications in Lima Region, Montana-Idaho

The syntectonic Beaverhead Formation, a thick unit of conglomerate and sandstone, records major tectogenic and morphogenic events in the Lima region of southwestern Montana and adjacent Idaho. Pollen and spore assemblages selected from critical stratigraphic positions within the formation are used to establish its age limits and to date the prominent tectonic elements which generated the sediments. Floral associations in the lowermost conglomerate beds, such as Tricolpites, Monocolpites, Eucommiidites, and monosulcate gymnosperm pollen, suggest a late Albian to late Cenomanian age for the basal Beaverhead. The middle part of the formation is assigned to the mid-Turonian to late Coniacian interval on the basis of relevant floral associations, such as Triatriopollenites, Proteacidites, Tricolpites, Eucommiidites, and Appendicisporites. The combination of Aquilapollenites, Momipites, and Proteacidites in the remaining third of the unit is indicative of a latest Cretaceous to mid-Paleocene age for the upper Beaverhead Formation. Although some reworking of Paleozoic spores is evident, most of the recorded palynomorphs suggest that Beaverhead sedimentation began as early as late Albia and persisted into the middle to late Paleocene. The tectonic elements which generated the Beaverhead sediments and later deformed them are the Blacktail-Snowcrest arch, the Ancestral Beaverhead Range, uplift in the geosyncline of central Idaho, and northwest-trending upthrusts. The first three elements originated concurrently, approximately during the late Albian to late Cenomanian, and remained the dominant influence on Beaverhead deposition and deformation until the mid-Paleocene. The younger Tendoy, Cabin, and Fritz Creek northwest-trending upthrusts originated in mid-Paleocene time and continued into the late Paleocene or early Eocene.

Seismic amplitude anomalies associated with thick First Leo sandstone lenses, eastern Powder River basin, Wyoming

Several new discoveries of oil production in the Leo sandstone, an economic unit in the Pennsylvanian middle member of the Minnelusa formation, eastern Powder River basin, Wyoming‐Nebraska‐South Dakota, have renewed exploration interest in this area. Vertical seismic profiles (VSP) and model studies suggested that a measurable seismic amplitude anomaly is frequently associated with the thick First Leo sandstone lenses. To test this concept, a surface reflection seismic profile was run between two wells about 12 miles apart. The First Leo was present and productive in one well and thin and barren in the other. The surface profile shows the predicted amplitude anomaly at the well where a thick lens is known to exist. Two other First Leo amplitude anomalies also appear on the surface seismic profile between the two wells, which may indicate the presence of additional lenses.

Interpreted Reflection Seismic Events Near the North Central Corporation Well, Newark Basin, Bucks County, Pennsylvania

dril led a 10,500-ft well in Bucks County, Pennsylvania, to test for oil and gas in TriassicJurassic strata of the Newark Group in the Newark basin. The hole was located about 5 mi southeast of the border fault on the crest of the Revere anticline, a transverse structure that plunges northwestward to-ward the border fault on the crest of the Revere anticline, a transverse structure that plunges northwestward toward the border fault. This drill hole, No. 1 Cabot-KBI, penetrated in descending order 2900 ft of lacustrine red and gray shale (Passaic Formation of Jurassic and Triassic age), 3600 ft of Lacustrine gray and black shale (Lockatong Formation of Triassic age), and 4000 ft of fluvial sandstone and red shale (Stockton Formation of Triassic age). Although the drill hole was abandoned, it revealed excellent gas shows throughout the Lockatong Formation and parts of the Stockton Formation. Acoustic and density logs from the well were converted to a synthetic seismogram that ties stratigraphic intervals in the borehole with seismic events on the nearby, 33-mi-long Seitel ND-l seismic line. Formation contacts, probable intraformational unconformities and lithologic units such as 50-ft-thick fluvial sandstones in the Stockton Formation are identified and traced for tens of miles away from the well. Moreover, beneath the drill site in the Stockton Formation, the 48-fold seismic line shows a large anticline that is subparallel to the border fault. This anticline has no surface expression; Interpreted reflection seismic events near the North Central Corporation Well, Newark Basin, Bucks County, Pennsylvania

Depositional setting of Ordovician and Cambrian rocks in central Appalachian basin along a section from Morrow County, Ohio, to Calhoun County, West Virginia

A 200-mi (320 km) long restored stratigraphic section from Morrow County, Ohio, to Calhoun County, West Virginia, contrasts Ordovician and Cambrian rocks deposited on a relatively stable shelf with those deposited in rift and postrift basins. Lithologic data are from commercial logs and from detailed descriptions of cores in five of the nine drill holes used to construct the section. Particularly instructive was the 2,352 ft (717 m) of core from the Hope Natural Gas 9634 Power Oil basement test in Wood County, West Virginia. Rift basin deposits are dominated by medium to dark-gray argillaceous limestone, argillaceous siltstone, and by green-gray to black shale of probable subtidal origin. Dolomite is the dominant rock type in the postrift basin and adjacent stable shelf deposits. The upper part of the postrift sequence, composed of the Middle Ordovician Black River Limestone, the Middle Ordovician Trenton Limestone, and Middle and Upper Ordovician Antes (Utica) Shale with a high organic content, represents deposition in gradually deepening water on an open shelf.

Stratigraphic Framework of Cambrian and Ordovician Rocks Across Rome Trough, Central Appalachian Basin: ABSTRACT

Restored stratigraphic cross sections drawn primarily through the subsurface of parts of Pennsylvania, Ohio, West Virginia, Kentucky, and Tennessee provide new detailed information to further the understanding of Cambrian and Ordovician sedimentation and tectonics associated with the Rome trough sector of the Appalachian basin. Drilled thickness of the Cambrian and Ordovician sequence ranges from a maximum of about 14,500 ft (4.5 km) along the axis of the trough to a minimum of about 3500 ft (1 km) on the western flank.

Petroleum Source-Rock Potential of Pennsylvanian Black Shales in Powder River Basin, Wyoming, and Northern Denver Basin, Nebraska: ABSTRACT

We analyzed 70 black shale samples from the middle member of the Minnelusa Formation (Pennsylvanian) in the Powder River basin of Wyoming and South Dakota, and from equivalent rocks of Desmoinesian age in the northern Denver basin of Nebraska. Organic-carbon content of these shales ranges from less than 1 to 26 wt. % (average = 5.4 wt. %). The shales contain predominantly type II organic matter and yield an average of 27,000 ppm hydrocarbons upon pyrolysis (S2 yield, Rock-Eval). These data indicate that the shales are excellent potential source rocks. Thermal maturation data (vitrinite reflectance, pyrolysis, hydrocarbon geochemistry) indicate that some hydrocarbon generation has occurred, although complete generation of available hydrocarbons has not occurred or the samples analyzed in this study. We analyzed 12 oil samples from fields producing from the Minnelusa Formation, for comparison with extracts from the black shales. Two, and possibly three, genetic oil types are produced from sandstone reservoirs in the Minnelusa Formation. One type is produced from sandstone reservoirs in the upper member (Permian), and a second type is produced from the middle member Leo sandstones (Pennsylvanian). This second oil type can be subdivided into two subgroups based on chemical composition, although we cannot determine from our data whether these are genetically distinct oils. Extracts from the black-shale samples correlate well with the two or three oil types based on stable carbon isotope composition and detailed molecular hydrocarbon composition determined by gas chromatography-mass s ectrometry (C9+ alkanes and biomarkers). These results suggest that oil produced from the upper and middle members of the Minnelusa Formation in the Powder River basin is derived locally from the Pennsylvanian black shale and is not a product of long-range migration from the Phosphoria Formation in western Wyoming. End_of_Article - Last_Page 935------------

Seismic Models of 15 Stratigraphically Controlled Oil and Gas Fields Containing Sandstone Reservoirs in Rocky Mountain Basins: ABSTRACT

Two-dimensional, normal-incidence, ray-theory seismic models were generated for 15 stratigraphic traps which have accumulated oil and gas in the Rocky Mountain province. The investigation is a feasibility study to determine the seismic character of moderate-sized (6-30 m thick), lenticular sandstone reservoirs in Rocky Mountain basins. The models are noise free and do not include all the complexities of the seismic phenomenon, but they do provide a reasonable indication of the anomaly to be expected for a specific problem and the quality of seismic data required to solve it. The fields chosen for the model studies represent different kinds of stratigraphic traps, and the reservoirs range in age from Late Pennsylvanian to Late Cretaceous. The fields include nine from the P wder River basin, three from the Denver basin, two from the Green River basin, and one from the San Juan basin. Each seismic model was constructed from a detailed geologic cross section and typically consists of 30 layers and several hundred velocity and density values. Effects of inelastic attenuation, interbed multiples and diffractions, are not incorporated in these seismic models. Hydrocarbon effects should be partly represented through the response of acoustic and density logs from which the models were derived. Final synthetic seismic sections are displayed with symmetrical Ricker wavelets at three different frequencies. Many of the 15 fields investigated appear to be detectable on conventional seismic sections, although several of the anomalies are very subtle. The seismic expression of the objectives modeled are manifested by amplitude changes due to acoustic contrasts at stratigraphic boundaries, or to constructive interference of waveforms. End_of_Article - Last_Page 778------------

Middle Member of Minnelusa Formation (Middle and Upper Pennsylvanian)--Implications for Stratigraphic-Trap Oil Accumulations in Powder River Basin, Wyoming: ABSTRACT

The middle member of the Minnelusa Formation (Middle to Upper Pennsylvanian) thins northward across the Powder River basin from about 150 m thick in the Hartville uplift to less than 50 m near the Wyoming-Montana border. Much of the thinning occurs beneath a regional, pre-Permian unconformity, which is identified in the south half of the basin by a mudstone commonly identified as the red shale marker. Cyclically arranged units up to 10 m thick, composed in ascending order of black organic-rich shale, mud-supported dolomite, anhydrite, and quartzose sandstone, characterize most of the middle Minnelusa. The majority of the sandstone units (informally designated in the subsurface as the Leo sandstones) are less than 3 m thick, tabular shaped, and commonly cemented with anhydrite and dolomite. Locally, however, the sandstones, particularly in the first Leo interval, are lenticular and linear, very porous, and attain thicknesses of more than 15 m. Several of these 10 to 15-m thick, linear first Leo sandstone bodies trend northwest across the southern Powder River basin. They probably represent wadi-type channels that have cut across sabkha and associated peritidal deposits during low st nds of sea level. The source of the Leo sandstones is presently uncertain, but at least the lowermost ones appear to be distal equivalents of the Tensleep Sandstone (Desmoinesian) to the northwest. Where the thicker sandstone units of the first Leo cross anticlinal noses such as at Red Bird, Pine Lodge, and Little Buck Creek, they commonly contain stratigraphically trapped oil. The oil in these fields was probably locally derived from the thin (0.5 to 2 m), widespread, black organic-rich shale units in the middle member. The lenticularity, proposed northwest trend, thickness, porosity, and associated probable source rocks make these sandstone units prime targets for oil and gas exploration in the sparsely tested, deep, southern Powder River basin. End_of_Article - Last_Page 778------------