Escape Of Fluids Research Articles

Petroleum Geology of Solimoes Basin, Brazil

Solimoes basin is located at the northwestern portion of the South American continent, adjacent to a subandean pericratonic belt. It constitutes a Paleozoic intracratonic basin covering an area of about 600,000 km[sup 2] and displaying a maximum sedimentary thickness of 3400 m. The tectono-sedimentary evolution can be largely related with important events that occurred at the western border of the continent. The regional flexural subsidence and tectonic deformation observed are correlated to two major phases: Pre-Andean (Paleozoic) and Andean (Mesozoic and Cenozoic). In the Andean phase, compression with shear components, of Triassic age, known as the Jurua Tectonism, became very important for oil exploration of the basin. The stratigraphic conditions considered of greatest interest for petroleum exploration comprise Devonian gas and oil sourcing shales and Carboniferous sandstones reservoirs with an evaporitic seal. The main traps are anticlines related to reverse faults. In this context, Petrobras discovered Jurua gas field in 1978 and the Rio Urucu gas and oil field in 1986. These were the first fields discovered in Brazilian Paleozoic basins. Total petroleum fields discovered in Brazilian Paleozoic basins. Total petroleum reserves discovered represent 400 million bbl of equivalent oil. Present migration and accumulation call for previous accumulation in intrabasinalmore » Paleozoic highs and related stratigraphic traps. Late tectonism seems to have resulted in redistribution and/or escape of fluids into new traps. Less disturbed areas are expected to contain original accumulations.« less

Genesis of Gold Deposits in Chugach Terrane of South-Central Alaska--Evidence from Fluid Inclusions: ABSTRACT

Gold-bearing quartz veins occur in shear zones, faults, and joints within the Upper Cretaceous Valdez Group flysch in the Kenai and Chugach Mountains of south-central Alaska. The veins are regionally restricted to areas of medium greenschist-grade metamorphic rocks and are notably absent in lower and higher grade metamorphic rocks. Fluid inclusion studies were conducted on samples of gold-bearing quartz from the Moose Pass, Hope-Sunrise, Port Wells, and Port Valdez districts. Ice and clathrate melting temperatures indicate that the ore-forming fluids had low salinities, ranging from 0 to 5-equivalent wt. % NaCl. These fluids contain appreciable amounts of dissolved gases, as shown by the nearly ubiquitous formation of clathrates during inclusion freezing and by the common presence of three-phase inclusions consisting of aqueous fluid, liquid CO2, and vapor. Total gas content varies from essentially nondetectable to as much as 10 vol. %. Freezing measurements on the inclusion fluids show the gas composition to vary from nearly pure CO2 to mixtures dominated by CH4 and N2We believe that the gold-bearing veins represent pathways for the escape of metamorphic fluids during rapid uplift of the Chugach and Kenai Mountains. The veins are believed to have formed along hydraulic fractures or along dilated preexisting fractures, created when fluid pressure exceeded load pressure. End_of_Article - Last_Page 665------------

Design of Pipelines in Mudslide Areas

Summary A design strategy is presented for routing and configuring pipelines in mudslide areas. This strategy is illustrated with a case study of a pipeline in the Mississippi River Delta. The case study focuses on the geotechnical aspects of pipeline settlement, flotation, and analysis of mudslide forces and stresses. Introduction It is impossible to prevent pipeline failures in an active mudslide area. Key strategies to design pipelines that have acceptable cost and reliability in these areas includeminimum exposure to existing and potential locations of mudslides;minimum lateral soil forces;weighting to minimize penetration into the seafloor;analysis to establish soil loadings, restraints, flexibility, and ultimate strength of the pipeline; anddesign of terminals to incorporate flexibility, repairability, and control of escape of products. Design Strategy The primary objective of the pipeline design process is to design a system that will reliably process is to design a system that will reliably transport products during its lifetime at the lowest total cost. The pipeline design process (Fig. 1) must consider the constraints posed by environment, construction, operations, and design. These constraints are discussed next. Constraints Environmental constraints include definition of the waves, currents, mudslides, fault movements, soils profile, and bathymetry that can influence the pipeline during its lifetime. Construction constraints include the equipment used for fabrication and installation, pipeline steels, welding and quality controls, and pipeline bedding, backfill, and armoring. Operational constraints include desired tie-in points; volumes, pressures, temperature, and corrosivity of fluids to be transported, pipeline maintenance, pipeline repair, fluid pipeline maintenance, pipeline repair, fluid escape-control measures, and acceptable failure incidence. Design constraints include analysis methods to be used, routing guidelines, regulatory requirements and codes, allowable stresses, and factors of safety. Design constraints also include economic and impact considerations. Economic considerations include costs of construction, operation, failure, and repair. Impact considerations include potential effects of the pipeline on other operations and facilities, impacts of the pipeline on the environment, and social and political effects of failures. In view of these constraints, the pipeline designer has to gather the data and information needed to define the constraints at the outset of the engineering process. The design process then focuses on a logical balancing of these constraints to result in an optimal pipeline design. Of particular importance is the use of hazard mitigation techniques in the pipeline design process. Examples of such techniques include process. Examples of such techniques includebackflow valves to prevent escape of fluids,pumping or compression shutdown systems,breakaway couplings to control the points of failure,use of pipe coatings to minimize forces, andincorporation of failure detection and repair systems. Perhaps the most important hazard mitigation technique is perceptive siting and routing of the pipeline to avoid or minimize exposure to present and future hazards, which are discussed next. present and future hazards, which are discussed next. Routing Reconnaissance and Hazard Identification Perceptive routing of pipelines to avoid hazardous Perceptive routing of pipelines to avoid hazardous conditions starts with detailed surveys and geologic study of the potential routes. JPT p. 1985

Hydrothermal alteration of the Hahns Peak Stock, Routt County, Colorado

Hydrothermal alteration and associated lead-zinc-silver sulfide mineralization in the Hahns Peak quartz latite stock, Routt County, Colorado, form a zoned pattern which was identified by detailed geologic mapping plus petrographic and X-ray studies of clays, micas, and feldspars in surface and subsurface samples. Routine analysis of structural state and composition of alkali feldspars was an integral part of the X-ray studies.The two stages of alteration and mineralization identified within the stock are: pervasive albitization with minor deposition of disseminated pyrite and argillic and sericitic alteration strongly localized along fractures and breccia zones accompanied by deposition of pyrite, sphalerite, chalcopyrite, galena, and argentiferous tetrahedrite. The mineral assemblage of albite-orthoclase-quartz-sericite-pyrite indicated albitic alteration probably formed in the temperature range 400 degrees to 500 degrees C and the assemblage of sericite-dickite-montmorillonite-quartz-pyrite indicates that the sericitic and argillic alteration formed in the range of 250 degrees to 350 degrees C. Zones of advanced argillic and sericitic alteration crosscut the pervasive albitic alteration and grade outward into pervasive intermediate argillic alteration in less fractured rock.The mineralogic changes observed in the pervasive alteration zones are interpreted to be the result of gradual changes in solution composition as the hydrothermal solutions ascended in the stock. The mineralogic changes in the advanced argillic and sericitic zones are probably the result of more drastic changes in the solution composition caused by rapid escape of fluids due to release of pressure from structural readjustments in the stock. The changes responsible for sulfide deposition in the advanced argillic and sericitic zones probably were decreasing temperature, increasing pH of the solution, and increasing cation/H (super +) activity ratios in solution.

Clastic Sills and Dikes Associated with Deep-Water Sandstones, Tourelle Formation, Ordovician, Quebec

ABSTRACT The Arenigian Tourelle Formation is dominated by thick, coarse, graded sandstone layers. These poorly-sorted sands were deposited on submarine fans which formed in response to uplift during initiation of the Taconic orogeny. The base of the formation consists of interbedded red and green shales, and rippled dolomitic siltstones, and is injected in spectacular fashion by fine to coarse sandstone dikes and sills. Sills are the dominant type of injection and may exceed 3 metres in thickness. Depth of burial during injection was on the order of 20 to 60 metres, with sand mobilization being the result of liquefaction and perhaps the thixotropic behavior of a primary clay matrix. The source of injected sand in the Cap Ste-Anne section, which was studied in detail, is inferred to have been a sand-filled submarine channel to the southwest of the present outcrop area. Sand was injected laterally along bedding planes and upward from the base to the top of the sequence. Liquefaction was facilitated by sediment loading and compaction under a clay seal, and was triggered by (1) slumps, which are present in the section, and/or (2) earthquakes associated with contemporary orogenesis. Clastic injection did not occur at higher levels in the Tourelle Formation for want of an impermeable clay seal capable of preventing escape of excess pore fluids during compaction.

Relation of Methane Generation to Undercompacted Shales, Shale Diapirs, and Mud Volcanoes

Organic matter commonly makes up a substantial part of freshly deposited muds. During postdepositional history, much of this organic matter is decomposed by biochemical and thermochemical processes, with accompanying generation of methane within the sediments. Likewise during postdepositional history, weight of overburden brings about compaction of mud sediments through expulsion under pressure of interstitial pore water. However, at the same time as pressure on the fluid is tending to increase because of compaction and other factors, the permeability of the sediment tends to be reduced by closer packing of clay particles. Thus it may happen not infrequently that the escape of fluids from a mud or shale body may fail temporarily to keep up with the causes tending to incre se fluid pressure, and in such cases these bodies will become overpressured and undercompacted with respect to surrounding sediments. The generation of methane gas within these mud and shale bodies is an important added factor which tends further to accentuate, or even create, their overpressured, undercompacted state, both by building up additional internal pressure, and also by further impeding fluid expulsion because of the development of a second phase (gas) in the pore fluid. Because of the unstable, semifluid nature of methane-charged undercompacted muds or shales, they frequently find expression in mud or shale diapirs or in mud volcanoes. The importance to petroleum exploration of a causal relation between methane generation and undercompacted shales, shale diapirs, and mud volcanoes is principally that these features thus become indicators of areas or intervals where hydrocarbons have been, or are, actively originating. Although the nearby area of these overpressured features may be unfavorable for petroleum accumulation because of a lack of extensive reservoirs, the surrounding facies, above, below, and laterally adjacent, may be particularly favorable in their relation to both reservoir and source environments.