Estimating The Intrinsic Permeability Of Clastic Sediments From Geochemical Data

Clay and framework mineralogy, determined from geochemical well logging, are used with porosity to estimate the intrinsic permeability of elastic formations. The mineral abundances are first combined with their individual grain densities to yield a continuous matrix density log which is combined with the bulk density log to produce a very accurate porosity log. The maximum feldspar abundance is used as an indicator of textural and mineralogical maturity. The level-by-level abundances of framework grains, quartz and feldspar, slightly enhance the estimated permeability. The porosity, textural maturity, and framework grain abundances define a maximum permeability curve as a function of porosity. The clay mineral abundances act to reduce the observed permeability from this maximum permeability curve. For a given amount of clay, kaolinite is less harmful than illite, which is less harmful than smectite. The abundances of non-clay cementing agents such as calcite also decrease the permeability, but they are less harmful than the clay minerals. These concepts are embodied in the equation K = Af { 3/ (1 -)2 }exp(BiMi), where At represents the feldspar-dependent textural maturity term, Mi represents the abundance of the ith mineral, and Bi is a constant for the ith mineral. The Bi constants are positive for quartz and feldspar, negative for cements such as calcite or other carbonates, and negative for the clay minerals. Permeability is assumed to depend on porosity as described in the Kozeny-Carman equation. Geochemical log data were used to derive the mineralogy in wells from Venezuela, California, and Oklahoma. These mineral abundances were used to derive matrix density curves and porosities. Permeability was estimated from the above equation using identical values of Bi for all three wells. The derived permeability logs show good agreement with air permeabilities measured on core samples. Permeabilities ranged over more than six orders of magnitude; in the California well the range extended over four orders of magnitude.