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Porosity

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H. L. Vacher – One of the best experts on this subject based on the ideXlab platform.

  • Matrix permeability of the confined Floridan Aquifer, Florida, USA
    Hydrogeology Journal, 2004
    Co-Authors: David A. Budd, H. L. Vacher
    Abstract:

    El Acuífero Superior de Florida conserva gran parte de su porosidad deposicional y, como resultado, se comporta como un acuífero multi-poroso: de doble porosidad (acuífero poroso fracturado) a favor del buzamiento, donde se halla confinado, y de triple porosidad (acuífero poroso fracturado y kárstico) en sentido opuesto, en la zona en que se comporta como libre. La permeabilidad de la matriz en la región confinada está comprendida entre menos de 10^−14,4 y 10^−11,1 m^2, según determinaciones hechas a partir de 12.000 medidas de mini-permeámetro en 1.210 rodajas de testigos. Se ha distinguido quince clases texturales de calcita ( n =2.298) y dos de dolomita ( n =983), y las facies ejercen un gran control en la permeabilidad de la matriz. Como consecuencia, la arquitectura de las facies de los carbonatos Eocenos y Oligocenos que forman la zona confinada del acuífero controla la distribución lateral y vertical de la transmisividad de la matriz. Las facies más permeables son grainstones o grano-soportadas sin matriz (mediana de permeabilidad de 10^−12,4 m^2) y dolomitas sacaroideas (10^−12,0 m^2). Ambas son responsables de aproximadamente el 73% de la transmisividad de los testigos ensayados, aunque sólo constituyen el 24% de su espesor. El examen de las ecuaciones de flujo en acuíferos porosos fracturados sugiere que la permeabilidad de estas facies más permeables es lo suficientemente elevada como para no poder despreciar la permeabilidad de la matriz en la modelación hidráulica de dichos sistemas de doble porosidad. La proyección de la estratigrafía regional y de las tendencias de las facies en la parte del acuífero ubicado en sentido contrario al buzamiento, que tiene carácter de libre y está más karstificado, predice que las permeabilidades mayores son debidas al incremento de los porcentajes de grainstones y dolomitas sacaroideas. Por tanto, es probable que la transmisividad de la matriz deba ser tenida en cuenta en el sistema de triple porosidad de la región. L’aquifère floridien supérieur de la péninsule de Floride contient plus que sa porosité de dépôt et, par conséquent, est un aquifère à porosité multiple: double porosité (aquifère fracturé poreux) en aval-pendage, là où l’aquifère est captif, et triple porosité (aquifère karstique et fracturé poreux) en amont-pendage, dans la région où il est libre. La perméabilité de matrice dans la région captive est comprise entre moins de 10^−14,4 et 10^−11,1 m^2 d’après 12.000 mesures par miniperméamètre sur 1.200 m de carottes. Quinze classes texturales de calcaires ( n =2.298) et deux classes de dolomies ( n =983) ont été reconnues; il existe un fort contrôle du faciès sur la perméabilité. En effet, l’architecture des carbonates de l’Eocène et de l’Oligocène qui constituent la partie captive de l’aquifère contrôle la distribution latérale et verticale de la transmissivité de la matrice. Les faciès les plus perméables sont les grainstones ( k médian, 10^−12,4 m^2) et les dolomies saccharoïdes (10^−12,0 m^2). Ces deux faciès rendent compte de 73% environ de la transmissivité dans les carottes étudiées, bien qu’ils ne contribuent qu’à 24% environ de l’épaisseur. L’examen des équations d’écoulement en aquifères fracturés poreux suggère que la perméabilité de ces faciès les plus perméables est assez importante pour que la perméabilité de matrice ne puisse pas être écartée dans la modélisation de l’hydraulique de ces systèmes à double porosité. Si l’on projette ces tendances de la stratigraphie régionale et des faciès à l’amont-pendage, la partie non captive et karstifiée de l’aquifère laisse prévoir de fortes perméabilités dues à des pourcentages croissants de grainstones et de dolomies saccharoïdes. Il est donc très probable qu’il sera nécessaire de prendre en compte la transmissivité de matrice dans un système à triple porosité dans cette région. The Upper Floridan Aquifer of peninsular Florida retains most of its depositional Porosity and, as a result, is a multi-Porosity aquifer: double Porosity (fractured porous aquifer) downdip where the aquifer is confined, and triple Porosity (karstic, fractured porous aquifer) in the updip, unconfined region. Matrix permeability in the confined region varies in the range

Qiu Long – One of the best experts on this subject based on the ideXlab platform.

  • A New Type of Secondary Porosity–Quartz Dissolution Porosity
    , 2020
    Co-Authors: Qiu Long
    Abstract:

    As one of the most stable petrogenetic minerals in clastic reservoir, quartz is generally considered to be indissoluble to directly form secondary Porosity during diagenesis, and the dissolved rim of quartz in reservoir has been thought to be the result of dissolution of cements that substituted quartz formerly. In this study, quartz was found to have been dissolved directly in the reservoir of Hetaoyuan formation in Biyang depression, and form a new genetic type of Porosity, i.e. quartz dissolution Porosity, which is one of the most important Porosity types in reservoir in the studied area. The dissolution of quartz reaches 2%~7%, and sometimes up to more than 8% of microscopic Porosity in the reservoir rock,, which accounts for 10%~35% of total Porosity. Several lines of microscopic evidence for quartz dissolution are listed as follows: (1) Partial dissolution of clastic quartz. Quartz was dissolved partially to form irregularly rim, isolated grains, intercrystalline pores, sometimes quartz grains can be dissolved partly, and even completely, and result in the formation of stretched pores. (2) Dissolution of quartz develops along contact seam, the opening of contact seams can form irregular pore throat, which couldnot be the result of dissolution of quartz substituting cements. (3) Partial dissolution of quartzose detritus, the erosion of the detritus is obvious, and sometimes it can form honeycombed micropores. (4) Shape of carbonate components, both carbonate cements and debritus do not show much dissolution in reservoir rocks of the studied area, however, adjacent quartz grains were dissolved obviously, this further reveals that quartz was dissolved directly. Quartz dissolution in the studied area is the result of sedimentary environment, diagenesis, and evolution of formation water. Biyang depression was an arid to semi arid subtropical enclosed fault trough lake during deposition, and the depositional environment of which was an alkaline lake. The original formation water of the reservoir was alkaline to strong alkaline. As a result, together with the influence of alkaline strata, formation water remains its alkalinity mostly during the stages of burial diagenesis. Under such environment, quartz was unstable and easily dissolved. However, early diagenetic stage B is the most important formation period of quartz dissolution and such genetic type of Porosity. The existence of aboundant quartz dissolution pores provides new possibility for the interpretation of quartz dissolution itself, SiO 2 cement, secondary Porosity formation, as well as for reservoir prediction and evaluation in clastic reservoir.

Huining Xu – One of the best experts on this subject based on the ideXlab platform.

  • numerical study on seepage flow in pervious concrete based on 3d ct imaging
    Construction and Building Materials, 2018
    Co-Authors: Jiong Zhang, Ruiping Ming, Li Li, Huining Xu
    Abstract:

    Abstract Pervious concrete specimens are prepared for CT (Computed Tomography) imaging and numerical simulation to observe pore characteristics and study law of seepage flow. 3D reconstruction based on CT imaging is utilized to generate virtual 3D pervious concconcrete structures, extract the connected pore network models, and analyze the target Porosity, actual Porosity, 3D Porosity etc. Pore characteristics analysis shows the 3D Porosity, and average planar Porosity can generally represent the actual Porosity, and 3D connected Porosity is close to the effective Porosity. The connected pore network models are used to simulate the water seepseepage flow using CFD (Computed Fluid Dynamics) method. The seepage flow simulation shows the permeable capacity increases clearly with increasing Porosity under the same inlet pressure. The relationship between seepage velocity and pressure gradient is obtained and fitted by the nonlinear Forchheimer formula. The acquired hydraulic conductivity can be used to assess the seepage flow capacity.