Blanket Deposition Research Articles

Sulphide mineralization and wall-rock alteration in ophiolites and modern oceanic spreading centres

Sulphide mineralization and wall-rock alteration in ophiolites and modern oceanic spreading centres

Oil Potential of Western Gulf of Suez: ABSTRACT

Since 1886, Egyptian and foreign companies have explored the Gulf of Suez by classical mapping and geophysical techniques. During that time 13 oil and gas fields have been discovered. Average daily production currently is of the order of 50,000 BOPD. Structurally, the western Gulf of Suez is divided into two major provinces: West Bakr and West Zeit. In the former, beds characteristically dip to the northeast; in the latter, they dip to the southwest, both in surface outcrop and in subsurface. Within each province, fields are located over structural traps. As a result of drilling it is apparent that the structures resulted from major movement during the early Miocene. A major unconformity occurs at the top of the lower Miocene Nukhul Formation; and the beds of the overlying middle Miocene Belayim Formation transgress on to rocks as old as Precambrian. The Nubia Sandstone, one of the best reservoirs, is a blanket deposit over the whole gulf ranging in thickness from 130 m (425 ft) to in excess of 660 m (2,150 ft). The Miocene sands are more sporadic in their distribution and thickness. Three depocenters are known in West Bakr, Shukheir, and Wacdi Dib areas. Further reservoirs of lesser importance are Cretaceous sands, 6.5 m (21 ft) to 32 m (105 ft) thick throughout the area, Eocene carbonates, and Miocene reefs. Production up to the present has been from structural traps; future expansion of production will depend upon our ability to locate stratigraphic traps. Sands sourced by the shales have seldom given high yields. The hope is that through the generation of depositional environment models it will be possible to define prospects where the optimum sand/shale ratio of 1/4 to 1/6 can be found. End_of_Article - Last_Page 479------------

4378383 Method of making conductive paths through a lamina in a semiconductor device

On the layer 12 a mask 3 corresponding to the desired pattern of holes 15 is provided with via openings 14 having overhanging walls. The layer 12 is selectively etched with a method where the etching attack takes place vertically to the layer surface, and wherein the mask 3 is thinned simultaneously, so that holes 15 are obtained having a cross-section increasing toward the mask 3. If subsequently material 16 for filling the holes 15 is applied in a blanket deposition these holes are completely filled when the material 16 has the same thickness as the layer 12 although the openings over the holes are decreasing with increasing thickness of the material 16. The layer 12 consists preferably of an insulation material, the mask 3 of positive photoresist, and the material 16 of a metal.

Reservoir Management of the Hartzog Draw Field

Summary The Hartzog Draw field is a recently discovered major oil reservoir in northeastern Wyoming. Initial reservoir performance indicated that the field soon would be depleted below the bubble-point pressure. To evaluate secondary recovery possibilities, the working interest owners, cooperated in an extensive reservoir study. Although there were some unique problems. both in evaluating reservoir data and in obtaining a unitization agreement, this effort led to the formation of the Hartzog Draw Unit within 5 years of field discovery. Secondary recovery by waterflooding has begun, and enhanced recovery possibilities are being evaluated. Introduction The Hartzog Draw field, discovered in 1975, is in the Powder River basin of northeastern Wyoming, (Fig. 1). There are 177 wells in the field, producing on 160-acre (647 x 10 3-M2) spacing from the Shannon sand at 9,400 ft (2865 m). Initial oil in place (IOIP) was 350 MMSTB (55.6x 10 6 stock-tank M 3). As the field was developed, pressure measurements revealed that reservoir pressure was dropping rapidly from the initial value of 5,000 psig (34.5 MPa). Reservoir fluid analysis indicated that the oil was an undersaturated black oil with a bubble point of 1,550 psig (10.7 MPa). Pressure reduction significantly below the bubble point would lower ultimate recovery if the field eventually were waterflooded. Prudent reservoir management required that the field be unitized. An operators committee was formed, and under the direction of various subcommittees an extensive reservoir analysis was conducted. This included geological correlation and mapping, reservoir fluid and rock analysis, pressure transient testing, and relative permeability tests. Reservoir simulation studies were conducted to predict remaining primary recovery and secondary recovery for various proposed methods. These efforts resulted in a recommendation to the working interest owners to unitize and begin secondary recovery immediately by waterflooding. The field was unitized in mid-1980, and waterflood facilities currently are being installed. A study of enhanced recovery possibilities by CO, injection is being conducted also. The objectives of this paper are (1) to present the geology. performance history, and reservoir properties of the Hartzog Draw field, (2) to describe the unitization process, and (3) to discuss the current status of field development and plans for enhanced recovery. Field Geology The Hartzog Draw field is a northwest-to-southeast trending, stratigraphically trapped hydrocarbon reservoir. The field is approximately 22 miles (35.4 km) long and from 1 to 4 miles (1.6 to 6.4 km) wide. Oil and gas production is from the Shannon sandstone member of the Cody shale of Upper Cretaceous age. The reservoir sands range from less than 5 ft (1.5 m) to more than 60 ft (18.3 m) thick (Fig. 2), and lie within a 20- to 90-ft (6- to 27-m) sequence of inter-bedded sand, silt, and shale. The Hartzog Draw discovery well is shown in Fig. 3 as a type log for the field. It is believed that the Shannon sand of Hartzog Draw was deposited in an offshore marine shelf setting. The sand originally was spread over the shelf as a blanket deposit. The reservoir was formed by southward-flowing marine currents, which reworked and redistributed the sand in an elongate bar-type deposit. These marine currents varied in strength and energy, as indicated by the sedimentary structures, which range from ripples to large scale trough cross-beds within the reservoir. The grain size of the sand ranges from fine to medium, with an average clay content of about 20%. JPT P. 1575^

Geology of Albion Group of Tuscarawas County, Ohio: ABSTRACT

The Albion Group is the Lower Silurian sequence that was deposited along the northwestern edge of the Appalachian basin. The Albion Group is composed of the Brassfield Limestone and the Clinton Sandstone Formations. The Clinton Sandstone is the major petroleum producing formation in Ohio. Cross sections and isopachous and lithofacies maps indicate that the Clinton Formation occurs as a blanket deposit or a series of overlapping sandstone bodies which intertongue with the Cabothead Shale to the west. Deposition is commonly interpreted to have occurred in a marine-deltaic environment. The sand bodies represent delta channel sands and offshore bars. Hydrocarbon accumulations are stratigraphically controlled by sand-bed facies changes or porosity pinch-outs. The key to petroleum exploration in the Clinton Sandstone is determining the orientation and extent of the sandstone bodies through subsurface mapping. End_of_Article - Last_Page 1015------------

Mathematical models of the geometry of blanket deposits of minerals : IF, 3R. SOVIET MIN. SCI. V8, N5, SEPT–oct. 1972, P516–520

Mathematical models of the geometry of blanket deposits of minerals : IF, 3R. SOVIET MIN. SCI. V8, N5, SEPT–oct. 1972, P516–520

Petrology and Paleogeography of Mississippian Madison Formation in Western Saskatchewan: ABSTRACT

In western Saskatchewan the Mississippian carbonate rocks may be categorized into 5 lithofacies, which individually or collectively can be used to assist the interpretation of the various environments of deposition. The five categories are: (1) impoverished calcareous mudstone, (2) skeletal calcareous mudstone, (3) micritic skeletal or nonskeletal sandstone, (4) poorly washed skeletal sandstone, and (5) calcite-cemented skeletal or nonskeletal sandstone. The impoverished calcareous mudstones dominate the lower part of the Mississippian succession, particularly in the southern part of the study area, where they are composed of bituminous and argillaceous materials as well as nonargillaceous calcareous mudstones. The impoverished calcareous mudstones probably represent sediments deposited in water below wave base on the seaward side of the shelf edge. Collectively, the skeletal lithofacies probably represent shelf-edge deposits. Calcite-cemented crinoidal sandstones accumulated as thick, elongate banks. The poorly washed sandstones are generally at the top and bottom of the banks and the interbank areas show outward gradations from micrite skeletal sandstones on the flanks of the banks to skeletal calcareous mudstones in the centers of the interbank areas. Micritic skeletal sandstones also form blanket deposits that commonly act as platforms upon which the crinoidal banks were built. The nonskeletal sandstones (primarily composed of oolites) probably represent subtidal deposits on the shoreward side of the shelf edge. In the central part of western Saskatchewan they are present in the lower part of the succession and pass laterally southward into shelf-edge deposits. Farther south they are found at higher stratigraphic levels, and they are in lateral continuity with and overlie shelf-edge deposits. The relationships suggest a regression of open marine conditions from north to south. If the Mississippian sequence of southeastern Saskatchewan is used as an analogy, a dolomite-evaporite facies representing a supratidal environment probably existed north of the subtidal deposits, that is, beyond the present subcrop edge of the Mississippian in western Saskatchewan. This postulated distribution of facies suggests that possible hydrocarbon reservoirs similar to those of the Virden area of Manitoba are present in subtidal and shelf-edge deposits along the Mississippian subcrop in Saskatchewan. End_of_Article - Last_Page 959------------

Mathematical models of the geometry of blanket deposits of minerals

Mathematical models of the geometry of blanket deposits of minerals

Early Pennsylvanian Currents in the Southern Appalachian Mountains

Measurement of more than 1200 cross-beds in lower Pennsylvanian sandstones of the southern Appalachian Mountains reveals a broad pattern of sediment transport to the southwest and west. Most of the sand appears to have been derived from the east and to have moved south-westward parallel to the axis of the Appalachian geosyncline. The pattern has a similar alignment to that in the Illinois basin, but it is at right angles to earlier Paleozoic dispersal directions in the Appalachian geosyncline. Little or no sand has been contributed from the Cincinnati arch. The cross-beds are in sheetlike sandstone formations; the sandstone is conglomeratic, contains plant impressions, and is composed of lenticular, channeling, quartzose sedimentation units. The variation in thickness and lateral persistence of sedimentation units is also reflected in a moderate variability of mean cross-bedding directions between adjacent formations, and even within the same formation. Cross-bedding variability between adjacent units is thought to be due to regional changes in the position and orientation of channel-way systems from deposition of one sandstone formation to the next. Changes of cross-bedding azimuths within the same formation may result from channel curvature of local meanderlike deposits or from channel migration as the sands coalesced into a blanket deposit.

Phosphate deposits of the former Japanese islands in the Pacific; reconnaisance report

Most of the deposits occur as an irregular mantle of phosphate or phosphatic clay over and between bizarre pinnacles of raised limestone. Phosphatic solutions from bird droppings attacked the limestone; further weathering and solution produced the phosphatic mantle and shaped the pinnacles. However, the best deposits on Angaur are blanket deposits under swamps and apparently represent further alteration of deposits ofthe first type.

Tungsten-bearing manganese deposit at Golconda, Nevada

The tungsten deposit lies just above the former high water level of Quaternary Lake Lahontan and a short distance east of Golconda, Nevada. Tungsten-bearing manganiferous and ocherous deposits underlie calcareous tufa. The tungsten ores lie blanketlike on an erosion surface which truncates tilted Triassic sediments. Beneath the blanket deposits are veins of similar mineralization which are thought to have provided the source of the overlying ores. The blanket deposits are sufficiently large and contain enough tungsten to justify economic development. The ore minerals are colloidal in origin, tungstic acid having been adsorbed in psilomelane and Iimonite while both were gels. Both the ore-bearing layers and the tufa are considered to be chiefly of hot spring origin rather than the result of precipitation from Lake Lahontan. A jarosite-bearing vein containing small amounts of tungsten crops out at a slightly higher elevation where the hot springs deposit has been removed by erosion. The vein cuts steeply inclined limestone which has been considerably altered to chert and highly silicified with the production of quartzose masses. This vein is thought to be indicative of a still lower level of mineralization than the veins immediately below the blanket deposits. It is believed mineralization started with chertification and silicification but ultimately resulted in precipitation of tungsten, iron, manganese, and tufa. The source of the tungsten is not exposed, but the existence of scheelite deposits in the vicinity suggests the possibility of underlying scheelite or perhaps wolframite-bearing veins.