Abstracts: 2007
History of the San Jacinto mercury mine; Baragua mountain range, state of Lara, Venezuela
The only mercury mine in Venezuela is located in the remote Baragua Mountain Range approximately 23 Km. north of the village of Aregue in the state of Lara. Between 1937 and 1941, a cinnabar (HgS) impregnated sandstone was exploited and a small unknown amount of mercury (Hg) was obtained. The mineralized sandstone that was extracted from the mine was broken into small pieces with sledge hammers by hand and placed into an oven fired with wooden logs. The low temperature generated (+ 365º C) was sufficient to convert the cinnabar mineral into the liquid element mercury (Hg), giving off sulfur (S) fumes into the atmosphere. The mining operation lasted four years and was plagued with difficulties, including serious accidents during the excavation of the galleries using dynamite.
In April 1968, the Venezuelan Department of Mines and Hydrocarbons initiated a geological and mining study in the region. The objectives of the project were: 1) to find additional cinnabar deposits in the vicinity of the old mine and 2) to quantify the extension of the mineralization in order to determine whether it was worthwhile undertaking further exploitation based on the price of mercury at the time. In order to achieve the goals of the project, a geological survey was performed in an area of 32 km2 around the mine together with geochemical analyses of samples collected from the surrounding hills and from the dry river beds. The drilling of shallow wells was planned in order to establish the extent of the mineralized sandstone interval with depth. The results of this study indicated that the cinnabar existed as impregnations in the fractures of a turbiditic sandstone layer of the Matatere Formation of Paleocene-Eocene age. This mineralized layer, oriented more or less in a northeasterly direction with steep dips of 50º to the northwest, is 256 feet (90 meters) long and four feet (1.5 meters) thick at the surface outcrop. During the two years the project lasted, no additional mineralized sandstone layers were found within the study area. The detailed geological survey as well as the geochemical analyses proved that: 1) the cinnabar mineralization was limited to one sandstone bed at the mine and 2) reserve calculations of the ore indicated that the quantity of mercury that could be produced from an accessible volume of rock was too small to merit additional exploitation and therefore of minor economic importance.
Competition and performance in oil and gas lease sales and development in the U.S. Gulf of Mexico OCS region, 1983-1999
This report studies petroleum lease sales and development in the U.S. Gulf of Mexico (GOM) Outer Continental Shelf (OCS) using estimated physical and economic measures of performance in offshore petroleum lease sales and development. The physical performance measures include the prospectivity index, expeditious index, and development productivity. The estimated economic performance measures include a profitability index and internal rate of return.
Empirical analysis of lease specific data suggests that the Gulf OCS is just as attractive to the big four oil and gas integrated firms as it was two decades ago. However, there is evidence of an influx of more players in petroleum lease sales and in the development of the region than there was two decades ago. There is also strong evidence from lease prospectivity results suggesting that the risk of lease development failure rises with firm size and water depth.
Regarding lease development productivity, a declining pattern in productivity with firm size from big to small is unmistakable, as is a declining productivity trend over time. Further, there is evidence of rising lease development productivity with water depth. For all categories of leases, the productivity rate in the early 1980s was significantly higher than productivity rate in the early 1990s, notwithstanding the fact that more leases were issued and drilled in the 1980s than in the early 1990s.
In general, our estimated measures of aggregate economic performance, the profitability index and internal rates of return, are relatively low in comparison to returns in the manufacturing sector during the period. The reported low profitability measures notwithstanding, we find that aggregate annual average rate of return on all leases issued from 1983 to 1994 increases with water depth and across time. The same pattern, however, is not evident in the late 1990s, probably because of data limitations. Also, the aggregate average rate of return increases with firm size leases in the 1980s, but no definitive trend is apparent across firm size in the 1990s.
Idle iron in the Gulf of Mexico
Offshore structures are installed to produce hydrocarbons, but at some point in time during the life cycle of the field, when the cost to operate a structure exceeds the income from production, the structure will exist as a liability instead of an asset. Federal regulations require that an offshore oil and gas lease be cleared of all structures within one year after production on the lease ceases. In recent years, the Minerals Management Service has begun to encourage operators to remove structures on producing leases that are no longer "economically viable." The purpose of this paper is to quantify the amount of idle iron that exists in the Gulf of Mexico and to describe its geographic distribution and ownership patterns. The basic question of what idle iron is and why it exists is addressed, followed by a discussion of the policy implications involved in the interpretation of federal regulations. Summary statistics that quantify and define the idle iron inventory is then presented.
Reservoir characterization of the Wilcox Miller sandstone in east-central Louisiana
The Paleocene Middle Wilcox interval in east-central Louisiana typically consists of 15 major, easilycorrelatable sandstone bodies; six of which are oil producers. Of these, the Miller sandstone is one of the important reservoirs within this 800-ft interval. From 1959 to the present it has produced approximately 1.1 million barrels of 40º to 49º API gravity oil within the four township study area (4N/6E, 4N/7E, 5N/6E, 5N/7E). The depositional framework of the sandstone bodies was determined from detailed correlation and mapping, using 1007 E-logs in a 144 square mile area. The Miller sands are interpreted as distributary channels and associated overbank bay fill facies deposited in a lower delta plain setting. This is evident from the detailed net sandstone geometry and overlying lignite that caps the Miller reservoir throughout the study area.
Stratigraphically trapped oil in the distributary channel system and associated facies is believed to haveoriginated in the underlying source rocks; then subsequently, it moved vertically up to its present position through faults and several levels of communicated sandstone bodies (stratigraphic capture). The extremely low southeastwardly dip (<1º) was sufficient to permit lateral movement of oil within the Miller reservoir where it is trapped in depositionally higher sandstone layers or against shale.
Organic geochemistry of Wilcox shale, coal, and oils: Concordia Parish, Louisiana
Results of an organic geochemical study of Middle and Lower Wilcox rocks and oils from a conventional core taken in Concordia Parish, Louisiana, helped determine the potential organic facies thermal maturity and enabled oil-rock correlations. The geochemical techniques applied included: (1) total organic carbon (TOC) and Rock-Eval analyses; (2) visual kerogen analysis for vitrinite reflectance and kerogen typing; (3) whole extract gas chromatography (gc); (4) whole oil gc; (5) pyrolysisgas chromatography (py-gc) of S1 and S2 , and (5) gas chromatography-mass spectrometry (gc/ms) of saturate biomarkers on rock and oil samples. Kerogen microscopy shows a 0.44% Ro mean reflectance for both the coals and the shales and places the coals within the thermally immature lignite - subbituminous rank. Based on the results of the TOC and Rock-Eval analyses, the rock samples were subdivided into four groups according to variations in TOC, hydrogen indices (HI), oxygen indices (OI), and kerogen type.
Results of the kerogen petrography analyses indicate that coals and shales are petrographically different, in that the coals contain much smaller amounts of structured lipids and no amorphous kerogen. The maceral contents of the coals suggest they were deposited in a lower delta plain environment in fresh water marsh and swamp facies. Within the four groups of rock, percentages of amorphous kerogen in the shales as well as kerogen types vary greatly within the sampled interval, with some having adequate potential for oil generation, some could generate gas and others with no oil and gas generating potential whatsoever.
Pyrolysis - gas chromatography (py-gc) S2 data suggest that the coals are capable of generating highly paraffinic crude oils at adequate maturity, whereas the shales would generate less waxy crude oils when mature. Also, the S2 py-gc chromatograms of the shales indicate they are all similar regarding their organic matter constituents.
Gas chromatography-mass spectrometry (gc/ms) analyses on saturate biomarkers (terpane m/z 191) show a close similarity among the coal and shale samples. One of the pentacyclic terpane peaks shows a bionomoretane representing terrigenous organic matter. Major contributors to some of the peaks are probably C30 demethylated hopanes which also indicate a contribution of terrigenous organic matter. The biomarker analyses of these samples also showed very low thermal maturities in agreement with the measured values of about 0.44% (mean value).
Terpane (m/z 191) and sterane (m/z 217) distributions from the biomarker analyses on oil samples within different intervals in the Minter reservoir are very similar, indicating the same organic matter and thermal maturity for both. Also, the terpane distribution in the oils indicates they are quite different from the coals and shales adjacent to the reservoir. The GC/MS data on the oils indicate they are mature and derived from a shaly source rock containing mixed organic matter with bacterial, algal, and terrigenous components. Equilibrium values in hopane isomerization (56%) and those in sterane isomerization (57%) of the oils indicate thermal maturities close to peak oil generation at 0.80 - 0.90% Ro.
Whole extract gas chromatograms show similarities between the coals and shales in that that they are immature and contain essentially terrestrial organic matter. However, the Minter oils were expelled at a thermal maturity of about 0.80 - 0.90 Ro and totally lack any correlation with the coals and shales.
Geology of the Wilds distributary channel complex: Wilcox group of east-central, Louisiana
The Wilds delta comprises a subsurface interval deposited during the transgressive systems tract within Paleocene middle Wilcox time. Because of excellent well coverage through this interval in a four township area of east-central Louisiana, precise mapping based on detailed e-log correlations was possible. Net sand mapping has provided a means of recognizing genetic facies architectures within the Wilds delta. A conventional core collected through the distributary channel portion of the Wilds provided the means of measuring the physical parameters within this thick (50' - 130') channel system.
X-ray radiography of selected intervals, thin section petrography, and detailed petrophysical evaluation indicate that channel fills can differ considerably in architecture within one deltaic system. The data show the Wilds distributary channel to consist mainly of subangular to subrounded, very fine to medium sized quartz grains. Occasional siltstones and shales are interbedded within the sandstone layers; the latter contain flaser bedding, planar laminations and rip-up clasts. Porosity within this predominantly sandstone portion of the channel averages 30%, permeability ranges between 91 and 524 md and average 280 md. Only in those intervals of the channel where the grains are totally cemented by calcite cement are the porosities very low (7%) and permeability is totally lacking. Hydrocarbon accumulations within the Wilds interval in central Louisiana is believed to be the function of stratigraphy, manifested in subtle traps sourced through vertical migration pathways.
Living on the edge of the offshore oil and gas industry: Did it make a difference for the incomes of coastal residents?
The objective is to see if the growth of offshore oil and gas development that took place between 1969 and 2000 resulted in cumulative economic effects that differentiate the economic experience and circumstances of residentsin Louisiana's coastal parishes from the residents of Louisiana's non-coastal parishes. A comparison of the average rate of growth in per capita personal income in coastal and non-coastal parishes revealed remarkably little difference over the entire study period, or for any of the sub-periods considered separately. Comparing the components of the growth, however, shows this equality is misleading during the initial two phases of "energy boom" (1969-80) and "price collapse," (1981-1985) because the contributors to growth were different. A factor which complicates the analysis is that onshore production in coastal parishes peaked early in the 1970s and then fell rapidly. Offshore production became relatively and absolutely much more important in the last half of the period and was largely a stabilizing force. But during this latter period there are no discernable differences between the components of per capita personal income growth of the two groups of parishes and the implication is, that in a broad regional context, the effects of offshore development were temporary and transitory, as were the effects of onshore development during the period, rather than cumulative or permanent. Demographic indicators in the parishes are consistent with this conclusion.
