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Effective porosity

About: Effective porosity is a research topic. Over the lifetime, 1199 publications have been published within this topic receiving 26511 citations.


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Journal ArticleDOI
Marco A. S. Moraes1
TL;DR: In this paper, the pore-fluid distribution in the Pendencia Formation is analyzed and microscopic heterogeneity related to the geometrical relationship between preserved primary porosity and diagenetically produced secondary porosity is the main cause of the observed high water saturation.
Abstract: Most of the hydrocarbon reservoirs in the Pendencia Formation, onshore Potiguar basin, northeastern Brazil, are fine- to coarse-grained deltaic and turbiditic lacustrine feldspathic sandstones which contain quartz and feldspar overgrowths, calcite, secondary porosity, dolomite, and chlorite as the principal diagenetic elements. Porosity in these rocks is a complex association of reduced primary porosity (5%), carbonate dissolution porosity (7%) and framework-grain dissolution porosity (6%). Each porosity type displays characteristic textural features which permit recognition and quantification in thin sections. The secondary porosity apparently was produced by corrosive fluids generated from adjacent or deeper shales. The effect of the diagenetic phases on permeability was distinct from their effect on porosity. Initially, quartz and feldspar overgrowths partially obstructed the pore throats, significantly reducing permeability. Later, replacement by calcite of grain or overgrowth boundaries followed by calcite dissolution generated the 8-micrometer-diameter pore throats that control the present permeability system. Among the late diagenetic phases, chlorite was the most harmful to reservoir permeability, affecting especially fine-grained sandstones. The present pore-fluid distributions in the Pendencia reservoirs show that high irreducible water saturations (S[wi] around 40%) are common. These high S[wi] have generally been attributed to chlorite aggregates. However, analysis of the pore structure reveals that microscopic heterogeneity related to the geometrical relationship between preserved primary porosity and diagenetically produced secondary porosity is the main cause of the observed high water saturation. Irreducible water tends to remain held within discontinuous patches of primary porosity as oil fills a continuous network of secondary porosity.

5 citations

Journal ArticleDOI
TL;DR: In this paper, an equation relating shale volume to porosity logs (neutron, density and acoustic logs), which takes into account the effect of matrix, fluid and shale parameters, is introduced.
Abstract: The volume of shale calculation based on naturally occurring gamma rays frequently overestimates shale volume when radioactive material other than shale is present, for example where sand appears to be shale. In this situation, shale volume calculations from other methods are highly recommended in order to avoid overestimation or underestimation of shale volume. This paper introduces an equation relating shale volume to porosity logs (neutron, density and acoustic logs), which takes into account the effect of matrix, fluid and shale parameters. This equation, which is based on the effective porosity definition and the Dresser Atlas (1982) equation, has been successfully applied to many shaly formations, regardless of the type and distribution of shale. Solved examples are used to test and compare this equation and the results come close to what actually exists, with the amount of error ranging from –5 to +5%. The advantages of the proposed equation can be summarised as: (1) it is a function of several parameters that affect the determination of shale volume in one formula; (2) it collects the three porosity tools for a more accurate calculation; and (3) it works best where radioactive material other than shale is present.

5 citations

Proceedings ArticleDOI
23 May 2011
TL;DR: In this article, the authors consider the modelling and upscaling of small scale patchy cements and evaluate the influence on oil-in-place calculation in a Triassic braided fluvial reservoir.
Abstract: This paper considers the modelling and upscaling of small scale patchy cements and evaluates the influence on oil-in-place calculation in a Triassic braided fluvial reservoir. The modelling method replicates the precipitation of cements over a background depositional facies. The detailed modelling on the transition zone where effective porosity may be low but saturation may be higher than expected in the uncemented matrix is the reason for teh increase in oil-in-place in a field-scale study.

5 citations

Journal Article
TL;DR: In this paper, the effect of fluid rock interaction on porosity of reservoir rocks in Tertiary System of Dongying Sag has been analyzed, and the results indicate that organic inorganic interaction and the amount of organic acid and CO 2 produced in the action in source rock pore fluid system are the key factors of the formation of porosity in sandstone.
Abstract: The effect of fluid rock interaction on porosity of reservoir rocks in Tertiary System of Dongying Sag has been analyzed in the paperThe results indicate:(1)organic inorganic interaction and the amount of organic acid and CO 2 produced in the action in source rock pore fluid system are the key factor of the formation of porosity in sandstone; (2)the dissolution of carbonate and aluminosilicate are the important fluid rock interactions to control porosity in sandstone; (3)the amount of carbonate in mudrock has an important influence on the scale of the formation of porosity in sandstone; (4)the abilities of inflow and outflow of fluid during fluid rock interaction determines the development of porosity in sandstoneDue to the influences of the geological and geochemical factors and fluid rock interaction,the three regional porous zones and three regional cemented zones are formed in the profile in Dongying Sag

5 citations

Proceedings ArticleDOI
TL;DR: Porosity reduction in siliceous sedimentary rocks is worthy of detailed study because the processes involved control the final porosity and permeability observed in all oil and gas reservoirs as discussed by the authors.
Abstract: Porosity reduction in siliceous sedimentary rocks is worthy of detailed study because the processes involved control the final porosity and permeability observed in all oil and gas reservoirs. In addition, porosity reduction and petroleum generation and migration may also be related. The effects on porosity reduction of the major porosity-controlling variables are virtually unknown and have been the subject of new experimental studies. Cores of St. Peter Sandstone have been subjected to high effective stress at room temperature and with fluid flow occurring at various rates. Relatively rapid pressure solution occurs even at room temperature in a flowing system.

5 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20236
202232
202162
202065
201971
201847