Browsing by Subject "Lower Wilcox"
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Item Evaluation of regional trends in production for Olmos and Lower Wilcox Lobo trends, onshore south Texas, USA(2020-05-06) Waltrip, Nelson William; Snedden, John W. (John William); Chuchla, Richard J. (Richard Julian)South Texas is home to many oil and gas producing geologic formations, including sandstones within the Upper Cretaceous Olmos Formation and Late Paleocene Lower Wilcox Lobo Formation. In the easternmost portion of the Rio Grande Embayment, Olmos Formation deposition occurred in shelf, shoreface, and deltaic paleoenvironments. Similarly, the Lobo formation was deposited in wave-dominated deltaic and shoreface environments in a shallow marine setting. Both plays are tight (low permeability) sandstone reservoirs that have produced significant amounts of hydrocarbons. Production analyses provide valuable insights into how different geologic factors effect production rates. Olmos Sandstone production areas can be differentiated by regional depositional environments. In Webb and Dimmit counties, updip trend reservoirs are characterized by thick, lobate deltaic sandstones while downdip trend reservoirs are thin, sheet-like marine shelf deposits. The AWP Field, located to the northeast, has three distinct depositional environments – delta front, slope, and basin plain environments. By contrast, the Lobo play can be subdivided by gross reservoir thickness across the whole play. Fault blocks related to regional uplift and gravity sliding in the Lobo formation provide a geologic basis to differentiate wells and production. Olmos downdip trend reservoirs, despite having apparently worse reservoir characteristics than those of the updip trend, yield better production results. Delta front reservoirs in the AWP Field have more favorable production trends than slope and basin plain reservoirs due to the superior reservoir qualities. It is hypothesized that the distribution of oil and gas in the AWP Field is a result of the timing of oil and gas generation and migration. Lobo production analyses reveal that thicker Lobo sandstone units result in better production rates. In addition, gas production does not seem to correlate to fault block reservoir volume in the Lobo formation. Base decline rates indicate how well a play or basin is able to maintain current levels of production as hydrocarbons are extracted. Conventional reservoir plays tend to have lower decline rates than unconventional or hybrid plays, where production declines rapidly. Base decline rates for Olmos and Lobo plays show meaningful similarities to and differences with base decline rates documented for the Permian Basin, which has seen an exponential increase in unconventional drilling. While production differences from region to region can be related to geologic factors and controls, production differences also contribute to differing levels of economic viability and exploitation. Since the Olmos and Lobo plays have been developed for decades and are nearing the end of their optimal development life, historical production data is used to build financial models as if each region has not been developed previously. This provides an economic perspective of which regions are better suited for investment and development based on their net present value (NPV) from a discounted cash flow analysis (DCA).Item Linking Gulf of Mexico margin submarine canyons to regional tectonics and interaction of Paleogene Lower Wilcox high frequency sequences with the Yoakum Canyon(2017-05) Clayton, Clarke Austin; Steel, R. J.; Olariu, CornelIn northern Gulf of Mexico, a clustering in a 100-150 km wide area of six Late Cretaceous-Paleogene age incisions up to 1000 m deep and 100 km long suggest a structural rather than eustatic control. The incisions counterintuitively align with the basinward trend of the San Marcos Uplift instead of forming in front of large sediment fairways (rivers) that formed depocenters of the Rio Grande and Houston embayments. The Sabine Arch and LaSalle Arch also uplift regions around the Gulf of Mexico Basin, which align with large slope incisions that indicate a possible main control of tectonism on canyon formation. This study proposes three new possible mechanisms, shelf edge bulge model, low uplift rate model (LUR), and high uplift rate model (HUR), for canyons formation in addition to the two ‘conventional’ models of cutting during lowstand (Posamentier et al., 1991) and cutting during transgression (Galloway, 1991). In addition to the tectonic control of canyon formation, canyon evolution can be longer lived than previously described for some of the Wilcox Group large-scale incisions. By mapping 12 high frequency regressive-transgressive sequences within the Lower Wilcox in the San Marcos Arch region: (1) Sand thickening patterns towards the Yoakum Canyon margin (2) Mis-match of log signature correlation across the Yoakum Canyon (indicating the canyon acted as a “sediment barrier” in the study region) suggest that canyon was active for a longer period than previously described.With the Yoakum Canyon being active during Lower Wilcox time, the canyon(s) evolution would be in the scale of 4 to 5 million years rather than 1 million to 100,000 years. Over this time scale, the deep-water sediment was delivered into the submarine canyon (s) when lateral switching of the shelf-delta depocenters reached close to the head of the canyon during delta transits across the inner to outer shelf. The relationship of Wilcox Group incisions with tectonics and long-lived evolution of canyons provides insight into the large volume of clastic sediment and possible new mechanisms for sediment delivery to the deep water Gulf of Mexico.