Browsing by Subject "Depositional environments"
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Item Paleogeographic evolution during the Eocene Upper Wilcox in the Houston embayment with consideration of the Yoakum Canyon fill(2015-05) Conwell, David Andrew; Steel, R. J.; Olariu, Cornel; Mohrig, DavidThe Eocene Upper Wilcox clastic wedge represents the second major pulse of terrigenous material into the Gulf of Mexico basin. Recent interest in the Wilcox has been reinvigorated by the drilling of the Baha prospect in 2001, and the associated discovery of 2.5 billion barrels of producible oil in deepwater Wilcox aged turbidite deposits. To better characterize and understand the deepwater deposits, research in the delivery systems that transported sediment from the Laramide uplift to the deep Gulf of Mexico is required, with a special focus on the Wilcox shelf margin. This study incorporates over 300 well logs, and outcrop to analyze the Upper Wilcox shelf deposits in the Houston Embayment. The area of this study extends from the outcrop belt in the north-northwest of the embayment down into the subsurface to the limit of down dip well control, around 150 km to the south-southeast. From west to east it extends from Gonzales County to Grimes County, around 200 km. In the Houston embayment the Upper Wilcox was previously interpreted as mainly being fluvial deposits that prograded across the relatively stable substrate provided by the underlying delta complexes of the Lower Wilcox. Previous authors have asserted that the Yoakum Canyon (Middle Wilcox) in the southwest of the field area had its entire 3,000’ filled with prodelta muds prior to the progradation of the Upper Wilcox. However, the present work shows that upper reaches of the Yoakum Canyon were filled by the sandstone units of the Upper Wilcox. Paleogeography maps, generated by differentiating between marine and terrestrial log signatures identify five distinct sequences in the Upper Wilcox. Each sequence shows linear sand trends across the shelf, generally in a north to south direction. A majority of sand was deposited in sequences three and four, through aggradation in the east and progradation in the west over the Yoakum Canyon region. The corresponding shorelines for sequences one through four remain largely pinned along the inherited shelf edge of the Lower Wilcox in the east, whereas the shorelines strongly prograde in the southwest over the Yoakum Canyon. With this new interpretation, that the Yoakum Canyon was not completely filled at the time of Upper Wilcox deposition, it is possible that the canyon delivered 2.86-7.15*106t/yr of sediment to the deepwater reservoirs. Outcrop measurements of cross strata, taken in Bastrop County, confirm the fluvial well log interpretation and provided a base for the volume calculations.Item Sequence stratigraphy and depositional systems in the Upper Cretaceous (Cenomanian) Woodbine Group, Anderson and Cherokee Counties, Texas(2016-08) Krueworramunee, Kullamard; Fisher, W. L. (William Lawrence), 1932-; Ambrose, William A.; Mohrig, DavidThe Woodbine Group of the East Texas Basin has attracted considerable interest because of its remaining petroleum resource in the deeper Woodbine pay. Recent estimate of the remaining petroleum resources in the East Texas field is approximately 1.58 billion stock tank barrels (BSTB) (Wang et al., 2008). However, expected ultimate recovery is limited by reservoir compartmentalization controlled by a complex stratigraphic framework. The purpose of this study is to define depositional systems and construct the stratigraphic framework of the Woodbine Group in Anderson and Cherokee Counties to provide the geologic context for characterizing remaining reserves. This study integrates core data and log data from closely spaced wireline logs (~1000 wells), using a chronostratigraphic method, to define sequence stratigraphic units. The stratigraphic framework of the Woodbine succession in the study area is composed of a maximum of 14 cycles in the basin axis, decreasing to a minimum of 3 cycles eastward to the Sabine Uplift and a minimum of 6 cycles westward to the out crop belt. The Woodbine succession is overlain by impermeable deposits of the Eagle Ford Shale and the Austin chalk as hydrocarbon seals. The complexity and heterogeneity of sandstone bodies in the Woodbine Group are largely controlled by depositional origin. Woodbine highstand and lowstand sequences display great variations in the depositional systems. The highstand deposits are composed mostly of fluvial dominated delta deposits that consist of distributary-channel, crevasse-splay, and delta-front deposits. Gamma-ray and spontaneous potential responses for these highstand deposits are upward-coarsening and serrate. In contrast, Woodbine lowstand deposits are mainly composed of coarse-grained sandstones of incised valley fills, reflecting relative base-level fall. These lowstand deposits, truncate older highstand deposits and are inferred from planar-based and blocky serrate log responses. Furthermore, highstand and lowstand deposits are overlain by transgressive deposits. These transgressive deposits are characterized by upward-fining log response, reflecting relative base-level rise. Correlation of sequence stratigraphic surfaces, sandstone-body stacking patterns and reservoir complexity inferred from gross-sandstone maps can lead to new exploration targets in the Woodbine Group in the southern part of the East Texas Basin.Item The depositional system for the Middle and Lower Wilcox in Houston Embayment, Northern Gulf of Mexico Basin(2016-08) Mercado, Lauren Kathleen; Olariu, Cornel; Steel, R. J.; Fisher, WilliamThe Paleocene-Eocene Wilcox formation has been a very oil and gas productive formation in the Gulf of Mexico. Recoveries are on the order of 40 to 500 million barrels of oil, but the potential exists to produce 3 to 15 billion barrels of oil. However, a number of technical and intellectual difficulties arise in economically producing the Wilcox Formation. Deep water Wilcox discoveries are located in low-permeability turbidite sandstones deposited in lower slope channels and basin floor fans in the Gulf of Mexico. The turbidite channels and fans are deep basin equivalents to the shelf delta systems located >250 miles updip, now below onshore Texas. It is important to understand the Paleocene-Eocene shelf depositional system dynamics as these are sediment feeders to the deep water turbidites and will provide a better understanding of the delivery system into the basin. This thesis focuses on the Middle and Lower Wilcox Formation specifically looking in the area of the Brazos and Colorado paleo-delta systems below the present day Texas coastal plain. The study areas represent shelf, shoreline and deltaic coastal deposits. The data used were well logs, such as gamma ray, spontaneous potential and resistivity. Using well log patterns the deposits have been broken down into six stratigraphic sequences on vertical logs, mapped, and analyzed. Signatures of log patterns also have been used to identify depositional systems from fluvial to coastal plain to the shelf in order to understand cycle stacking. The migration of the depocenters indicated a slight progradation, followed by retrogradation, followed by progradation caused by changes in accommodation and sediment supply. The analysis of the shelf and coastal depocenters suggest a possible complex link to the deep basin sediment transfer rather than a simple fluvial-delta-shelf-edge delta to deep water pathway.