Tubular Pores Research Articles

Application of a stochastic network pore model to oil-bearing rock with observations relevant to oil recovery

Mercury porosimeter experiments have been traditionally used to investigate the pore structure of oil bearing rocks, although interpretation based upon the oversimplified parallel-bundle model is inadequate to explain many practical aspects of oil recovery. A technique for stochastically assigning the sizes of tubular pore segments placed in a network configuration of interconnected pores has been used to model pore structure and a trial and erro procedure has been devised which gives directly the size distribution of segments comprising the network which will exactly reproduce any observed merc porosimeter penetration curve. The theory is applied to porosimeter tests on a core sample from the Agha Jari Field (Iran). It is evident that the pore distribution function according to a network interpretation comprises a very much greater proportion of larger pores than is inferred from the parallel model. This distortion of the pore size distribution is shown to arise from the inaccessibility of larger segments when surrounded by small pores, a phenomenon that cannot be represented by the parallel-bundle approach. As a quantified interconnecting pore model, the network analysis has potential for investigating oil retention mechanisms in a reservoir, and the probable micro-scale water displacement behaviour of the pore network deduced to rep the core sample is described. Low recovery factors seem to be related to water flowing preferentially through pathways made of larger pores. Entrapment likely in large pores isolated by surrounding smaller ones.

Calculation of hydraulic conductivities of horizons in some major soils in Wisconsin

Hydraulic conductivity between saturation and a tension of 100 cm water was calculated with moisture-retention data for nine soil horizons and compared with results from in situ measurements with the crust test. Agreement was good for sandy, apedal soil horizons with simple packing voids but only if matching factors were used. Results were unreliable in clayey, pedal soil horizons in which a few relatively large planar and tubular pores determine K in the measured tension range, whereas the greatest fraction of total porosity is composed of fine pores inside peds that hardly contribute to flow. Varying the number of pore classes ( n) and the water-filled porosity at saturation made no significant difference in the calculations for the apedal soils, but drastically changed the shape of the calculated curves for the pedal soils. Matching factors based on K sat measurement had to be used for all studied soil horizons, indicating that Marshall's pore-interaction model never predicted K sat accurately.

The random-spheres model for porous materials

In the “random spheres model” for porous materials the porous substance is assumed to consist of a large number of randomly overlapping solid microspheres, the void being constituted by the remaining space between the microspheres. For most porous materials this model is more realistic than the usual tubular pore models. The properties of the model are described, and some applications are presented, the most important being the calculation of the lifetime of a porous catalyst which is clogged by deposits.

Parametric study of the anode of an implantable biological fuel cell

In this paper, electrochemical oxidation of glucose at the concentration level present in human venous plasma is discussed, with the object of determining the feasibility of constructing an implantable fuel cell for powering a prosthetic heart. The model anode considered consists of a diffusing membrane, to prevent blood contact, backed by a porous electrode structure. The latter is assumed to consist of parallel tubular pores of length equal to the electrode thickness. The variation of membrane and electrode parameters and rate constants for glucose oxidation are considered as functions of reaction order and oxidation product under different flow conditions. It is shown that the least optimistic case, oxidation of glucose only to gluconic acid, is apparently marginally feasible.

Geologic Nomenclature and Classification of Porosity in Sedimentary Carbonates

Pore systems in sedimentary carbonates are generally complex in their geometry and genesis, and commonly differ markedly from those of sandstones. Current nomenclature and classifications appear inadequate for concise description or for interpretation of porosity in sedimentary carbonates. In this article we review current nomenclature, propose several new terms, and present a classification of porosity which stresses interrelations between porosity and other geologic features. The time and place in which porosity is created or modified are important elements of a genetically oriented classification. Three major geologic events in the history of a sedimentary carbonate form a practical basis for dating origin and modification of porosity, independent of the stage of lithification. These events are (1) creation of the sedimentary framework by clastic accumulation or accretionary precipitation (final deposition), (2) passage of a deposit below the zone of major influence by processes related to and operating from the deposition surface, and (3) passage of the sedimentary rock into the zone of influence by processes operating from an erosion surface (unconformity). The first event, final deposition, permits recognition of predepositional, depositional, and post epositional stages of porosity evolution. Cessation of final deposition is the most practical basis for distinguishing primary and secondary (postdepositional) porosity. Many of the key postdepositional changes in sedimentary carbonates and their pore systems occur near the surface, either very early in burial history or at a penultimate stage associated with uplift and erosion. Porosity created or modified at these times commonly can be differentiated. On the basis of the three major events heretofore distinguished, we propose to term the early burial stage the late stage telogenetic, and the normally very long intermediate stage mesogenetic. These new terms are also applicable to process, zones of burial, or porosity formed in these times or zones (e.g., eogenetic ceme tation, mesogenetic zone, telogenetic porosity). The proposed classification is designed to aid in geologic description and interpretation of pore systems End_Page 207------------------------------ and their carbonate host rocks. It is a descriptive and genetic system in which 15 basic porosity types are recognized: seven abundant types (interparticle, intraparticle, intercrystal, moldic, fenestral, fracture, and vug), and eight more specialized types. Modifying terms are used to characterize genesis, size and shape, and abundance of porosity. The genetic modifiers involve (1) process of modification (solution, cementation, and internal sedimentation), (2) direction or stage of modification (enlarged, reduced, or filled), and (3) time of porosity formation (primary, secondary, predepositional, depositional, eogenetic, mesogenetic, and telogenetic). Used with the basic porosity type, these genetic modifiers permit explicit designation of porosity origin and evolution. Pore shapes are classed as irregular or regular, and the latter are subdivided into equant, tubular, and platy shapes. A grade scale for size of regular-shaped pores, utilizing the average diameter of equant or tubular pores and the width of platy pores, has three main classes: micropores (< 1/16 mm), mesopores (1/16-4 mm), and megapores (4-256 mm). Megapores and mesopores are divided further into small and large subclasses. Abundance is noted by percent volume and/or by ratios of porosity types. Most porosity in sedimentary carbonates can be related specifically to sedimentary or diagenetic components that constitute the texture or fabric (fabric-selective porosity). Some porosity cannot be related to these features. Fabric selectivity commonly distinguishes pore systems of primary and early postdepositional (eogenetic) origin from those of later (telogenetic) origin that normally form after extensive diagenesis has transformed the very porous assemblage of stable and unstable carbonate minerals into a much less porous aggregate of ordered dolomite and/or calcite. Porosity in most carbonate facies, including most carbonate petroleum reservoir rocks, is largely fabric selective.