Dissolution porosity

Burley, S.D. Kantorowicz, J.D. (1986) Thin section and SEM textural criteria for the recognition of cement-dissolution porosity in sandstones. Sedimentology, 33, 587-604. 

Late cements causing post-dissolution porosity reduction include minor kaolinite and late ferroan calcite. Late ferroan dolomite is an important cement in all porous sandstones of the 0-35 well, where it reduced porosity by 4.2% on average (ranging from trace amounts to 20%). In the diage-netic maturity classification of Schmidt MacDonald (1979a) the Catalina Sandstone is semimature. 

The most common origin of secondary porosity in sandstones studied is due to dissolution of plagioclase or else dissolution of carbonate that replaced plagioclase. Replacement of silicate minerals by calcite is not uncommon, and much of the plagioclase dissolution porosity may actually be replacement-calcite dissolution porosity. We know of no way to resolve this problem. For purposes of calculations, we assumed that plagioclase was dissolved. 

The dissolution of framework grains and early dolomite cement has significantly enhanced porosity in many Latrobe sandstones. Within these sandstones, about 2 to 10% porosity is estimated to have been created by dissolution. The proportion of dissolution porosity relative to total porosity appears to increase with increasing burial. Above 2000 m (6500 ft), only minor enhancement of porosity was observed. With increasing depth, and... 

Having prepared the cements, a number of physical techniques were employed to study them. Porosity was determined by measuring the apparent volume and the solid volume, the former by straightforward linear measurement, the latter using a helium pycnometer. This technique was used to avoid the problems of dissolution that arise when water is used... 

The bioavailability of drugs from tablets can be markedly influenced by the rate and efficiency of the initial disintegration and dissolution process. Unfortunately, one is faced with a compromise situation — a structure that has both a durable structure prior to administration and the ability to readily break down when placed in the in vivo environment. One of the major factors affecting both these properties is the structure of the tablet, in particular its density (or porosity) and the pore structure. Study of the significance of such measurements and interpretation of the results is a relatively recent field of interest. 

The dissolution channels (wormholes), obtained under certain conditions of attack of carbonate rocks by hydrochloric acid, have been recently proven to have a fractal geometry. An equation was proposed, relating the increase of the equivalent wellbore radius (i.e. the decrease of the skin) to the amount of acid injected, in wellbore geometry and in undamaged primary porosity rocks. This equation is herein extended to damaged double porosity formations through minor modifications. 

One approach to the study of solubility is to evaluate the time dependence of the solubilization process, such as is conducted in the dissolution testing of dosage forms [70], In this work, the amount of drug substance that becomes dissolved per unit time under standard conditions is followed. Within the accepted model for pharmaceutical dissolution, the rate-limiting step is the transport of solute away from the interfacial layer at the dissolving solid into the bulk solution. To measure the intrinsic dissolution rate of a drug, the compound is normally compressed into a special die to a condition of zero porosity. The system is immersed into the solvent reservoir, and the concentration monitored as a function of time. Use of this procedure yields a dissolution rate parameter that is intrinsic to the compound under study and that is considered an important parameter in the preformulation process. A critical evaluation of the intrinsic dissolution methodology and interpretation is available [71]. 

The pore structure of a solid can contribute to the disintegration, dissolution, adsorption, and diffusion of a drug material [26,27]. Because of this, porosity and pore size distribution measurements have been used extensively to study tablets [28-30], granules [31,32], and excipients [33]. The following classification system of pore sizes has been developed based on the average pore radii [6] ... 

Dissolution time, tdi (for tablet) Tablet mass, m Diffusivity, D Grain particle size, dp Tablet size, 77 Porosity, e Order-of-magnitude model derived from Fick s and Darcy s laws [6] 2m2 td x2d2pH4Ds(l-s)2... 

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