Abstract Continuous core from the Marsing No. 16 well in the southwestern portion of the Uinta Basin, Utah, contains both siliciclastic and carbonate marginal lacustrine and nearshore open lacustrine lithologies. Overall, a long-term stratigraphic record of lake evolution, characterized by an expanding lake, is recorded upward from deltaic through open lacustrine deposits. Coincident with this overall trend of lake expansion is an apparent reduction in supply of siliciclastics to the depositional site and a marked delta retreat. Two contrasting suites of related environments that alternate in concert with changes in climate are postulated to explain the lithofacies recognized in the core. A "wet-climate model," distinguished by evidence for high lake levels combined with high fluvial discharge, is envisioned with a siliciclastic strand plain, lacking in dolomite, and containing channels that served as throughgoing delivery systems for clastics spewing out into the open lake. A "dry-climate model," with evidence for low lake levels combined with low fluvial discharge, consists of a dolomitic mud flat in which clastics are almost entirely lacking and practically the only limestone present occurs as shell-rich and coaly "lags" that represent brief lake-water incursions. Superimposed on a long-term, wet-dry-wet trend, are a succession of finer-scale depositional cycles that are best expressed in the dry part of the trend, in the marginal lacustrine sediment, as limestone-dolomite couplets, but may also be expressed in deltaic and open lacustrine deposits. The typical cycle begins with interspersed shelly limestone and coal deposited with the rise in lake level. This is succeeded by burrowed pelecypod- and ostracod-rich limestone, and is locally capped by strand plain-deposited, laminated, ostracod grainstone, or exposed mudflat-deposited dolomite. The counterpart in the deltaic environment is a coarsening-upward cycle, beginning with interspersed shelly limestone and coal, which is succeeded by burrowed and rippled siltstone and mudstone, and eventually root-mottled siltstone or massive sandstone. The black shale facies contains both oil-prone Type I and gas-prone Type III organic matter, with Type I volumetrically the more important. The open lacustrine limestones have the highest source potential, are oil-prone and immature, with total organic carbon averaging 3.1 percent. The vitrinitic coals within the basal portions of the lacustrine cycles are gas-prone, whereas the marginal lacustrine dolomites and clastics are lean.

Abstract Dolomite Reservoirs: Geochemical Techniques for Evaluating Origin and Distribution was written to address the need for a short, clear text that explains commonly used inorganic geochemical techniques and their application to dolomite petroleum reservoirs. This volume contains two parts. Part I consists of chapters on different geochemical techniques, with guidelines on how best to apply them, interpret the data, and recognize and avoid the pitfalls and misconceptions that are commonly encountered. Part II consists of case studies of dolomite petroleum reservoirs that formed in each of the major dolomitization environments. This publication will help geoscientists better understand the many ways in which geochemistry can be used to address dolomite reservoir problems.

Abstract In carbonate systems, dolomite often forms the best reservoirs. The dolomitization of carbonate sediments and rocks increases crystal size and pore throat size, and decreases pore roughness. Without exception, the combination of these increases the permeability of the carbonate. In this way, dolomitization “makes” the reservoir, with dolomite serving as the reservoir and the surrounding limestone forming the seal. Porosity in the dolomitic facies is enhanced in such cases not so much as a result of dolomitization, but through leaching of skeletal grains or evaporites, or by fracturing. Many environments of dolomitization have been identified. Some result in unique reservoir geometries that bear directly on exploration strategy. Therefore, it is important to gain a firm understanding of the process which controlled dolomitization early in the exploration history of a basin. In addition, dolomite is less reactive than calcite, so dolomite units are more resistant to porosity loss with depth than limestone units (Fig. 1) and the depth to “economic basement” is commonly greater for dolomite than for limestone. Therefore, the spatial distribution of dolomitized intervals within a carbonate section often defines the limits of reservoir development. The hydrologie process that dolomitizes a limestone can control the morphology of the dolomite body as well (e.g., supratidal dolomitization can produce thin, stratified, laterally extensive reservoirs, whereas subsurface fault-controlled dolomitization can produce narrow, linear, vertically extensive reservoirs). Therefore, to predict the spatial distribution of a dolomite reservoir, it is advisable to first determine the process that produced the dolomite. In carbonate

In order for a carbonate component to be used in constructing a marine isotopic baseline, one must be able to identify altered components and sample only unaltered components or the unaltered portions of partially altered components (Popp, et al., 1986a). Researchers working with the shells and skeletons of marine invertebrates and those working with marine carbonate cements have developed different approaches for obtaining original marine isotope values.