Lithofacies, Porosity and Log Response of the Lower San Andres Formation in the Palo Duro Basin

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Title: Lithofacies, Porosity and Log Response of the Lower San Andres Formation in the Palo Duro Basin
Author: Rahman, Ata Ur
Abstract: The lower San Andres Formation of Curry , DeBaca , Quay and Roosevelt counties , New Mexico , was deposited in the Tucumacari - Palo Duro Basin which was a swale on the Northwestern Shelf of the Permian Basin . Unlike other areas of the Permian Basin where San Andres forms prolific hydrocarbon reservoirs , in the study area it is devoid of hydrocarbons . The study of lithofacies distribution and associated depositional environments , porosity and permeability trends and geophysical log response could serve as a useful model in analyzing and interpreting other similar lithofacies . The lower San Andres consists of dolostones , limestones , dedolostones , anhydrite , halites and thin shales . Four major progradational depositional cycles are recorded . Upward from the base the cycles generally consist of subtidal and intertidal carbonates , supratidal carbonates , sulfates and halite . The vast bulk of the sulfate was emplaced as replacement of dolostones ; thus , the presence of anhydrite within a cycle may have little genetic significance . As compared to carbonates , percentages of anhydrite and halite increase both towards the NW (proximally ) and within successively younger cycles of deposition . Dolostones to limestone ratio also increases towards the NW and in younger cycles . Porosity and permeability generally increase towards the SE (distally ) and in older cycles of deposition . This reflects’ a general progradation of supratidal environments towards SE (distally ) . Primary porosities are very rarely preserved . Most of the preserved porosities are secondary , tertiary and quaternary in nature . Secondary intercrystalline porosity is more abundant in distal (SE ) areas , while moldic porosity is predominent in proximal (NW ) areas . Dolostones generally have much greater porosity than limestones . Most lower San Andres intervals have been subjected to two or more cyclic fluid invasions sequences wherein dolomitizing , anhydritizing and low salinity fluids have successively registered their overprints . Dolomite , anhydrite and calcite cements formed during multiple cyclic diagenesis are the prominant porosity occluders . Generally most of the lithofacies can be differentiated on the basis of the log response ; however , cross plots of various log values aid in differentiating the lithofacies more explicitly .
URI: http : / /hdl .handle .net /2346 /16709
Date: 1983-05


Lithofacies, Porosity and Log Response of the Lower San Andres Formation in the Palo Duro Basin. Master's thesis, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /16709 .

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