Browsing by Subject "dissolution"
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Item Assessing the influence of diagenesis on reservoir quality: Happy Spraberry Field, Garza County, Texas(Texas A&M University, 2004-09-30) Mazingue-Desailly, Vincent Philippe GuillaumeIn the Permian Basin, strata of Leonardian age typically consist of interbedded carbonates and siliciclastics interpreted to be turbidite deposits. Happy Spraberry Field produces from a 100-foot thick carbonate section in the Lower Clear Fork Formation (Lower Leonardian) on the Eastern Shelf of the Midland Basin. Reservoir facies include oolitic- to-skeletal grainstones and packstones, rudstones and in situ Tubiphytes bindstones. Depositional environments vary from open marine reefs to shallow marine oolitic shoal mounds. Best reservoir rocks are found in the oolitic-skeletal packstones. Diagenesis occurred in several phases and includes (1) micritization, (2) stabilization of skeletal fragments, (3) recrystallization of lime mud, (4) intense and selective dissolution, (5) precipitation of four different stages of calcite cement, (6) mechanical compaction, (7) late formation of anhydrite and (8) saddle dolomite and (9) replacement by chalcedony. Oomoldic porosity is the dominant pore type in oolitic grainstones and packstones. Incomplete dissolution of some ooids left ring-shaped structures that indicate ooids were originally bi-mineralic. Bacterial sulfate reduction is suggested by the presence of (1) dissolved anhydrite, (2) saddle dolomite, (3) late-stage coarse-calcite cement and (4) small clusters of pyrite. Diagenetic overprinting on depositional porosity is clearly evident in all reservoir facies and is especially important in the less-cemented parts of the oolitic grainstones where partially-dissolved ooids were subjected to mechanical compaction resulting in "eggshell" remnants. Pore filling by late anhydrite is most extensive in zones where dissolution and compaction were intense. Finally, a porosity-permeability model was constructed to present variations in oolitic packstone- rudstone-bindstone reservoir rocks. The poroperm model could not be applied to oolitic grainstone intervals because no consistent trends in the spatial distribution of porosity and permeability were identified. Routine core analysis did not produce any reliable value of water saturation (Sw). An attempt to take advantage of wireline log data indicates that the saturation exponent (n) may be variable in this reservoir.Item Early Miocene Carbonate Dissolution in the Eastern Equatorial Pacific(2014-11-19) Wilson, Julia KeeganAs the world?s largest ocean, the Pacific Ocean is intrinsically linked to the major changes in current and past climate via several mechanisms, in particular, through the carbon cycle?s influence on atmospheric CO2 concentrations. One way to understand the ocean carbon cycle is to study fluctuations in the CaCO3 content of ocean sediments and determine the nature, timing, and drivers of those events. As part of a larger effort to reconstruct Cenozoic paleoclimate in the eastern equatorial Pacific, XRF records are used here to define an early Miocene low CaCO3 event in the equatorial Pacific that corresponds to the seismic horizon termed ?Lavender?. The low CaCO3 interval is correlated at submeter scale in 4 drill sites from IODP Expedition 320/321 and has been identified by seismic reflection throughout the region, indicating a large perturbation in the global carbon cycle at the time of its deposition. Using multi-element XRF data, we have determined that this event was caused by CaCO3 dissolution, with peak dissolution occurring at 16.9 Ma. The event begins prior to the Miocene Climate Optimum (MCO) with peak dissolution coinciding with the initial warming step of the MCO. Three potential disrupters of CaCO3 deposition are investigated: a change in organic carbon burial to the deep ocean, reducing deep dissolved inorganic carbon (DIC); a change in mantle CO2 outgassing associated with the formation and emplacement of the Columbia River basalt province; and basin-basin fractionation, where development of a new CaCO3 depocenter in the Atlantic reduces CaCO3 deposition in the Pacific. Of these 3 possibilities, the timing of the Lavender event favors basin-basin fractionation.