Browsing by Subject "Depositional system"
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Item Depositional systems and sequence stratigraphy of the M1 sandstone in Tarapoa, Ecuador(2014-12) Ye, Yu; Steel, R. J.; Olariu, CornelCampanian M1 Sandstone is one of the major prospective sandstone units in the Tarapoa field in Oriente Basin, Ecuador. The M1 Sandstone is always markedly sharp based, averages 25 m in thickness, shows upward increasing marine bioturbation and generally fines upward from coarse to very fine grained sandstone. In cores, the sandstones at base are amalgamated coarse to fine grained with prominent cross stratification (dm thick), sometimes clearly bi-directional and contains mud drapes. These suggest strong tidal or fluvial-tidal currents in estuary channels or delta distributary channels. The finer grained intervals in the middle are brackish-water intensely bioturbated and dominated by mud drapes, wavy and flaser bedding suggestive of intertidal flats. Associated overlying coals and coaly shales suggest supratidal conditions. The sandstones at top are cross stratified and contain mud drapes. These again suggest strong tidal or fluvial-tidal currents in estuary channels or delta distributary channels. The stacking pattern of facies in M1 Sandstone reveals the evolution of the M1 depositional system, as well as the sequence stratigraphy of M1 sandstone. The evolution includes four stages of deposition which indicates an initial sea level rise, a subsequent sea level fall, and another sea level rise. Lateral sand-mud heterogeneity exists in the study area, forming “shale barriers”, i.e. elongate shale-rich zones that are lateral barriers to hydrocarbon migration. They are interpreted to be abandoned tidal channels filled with muddy tidal flat deposits during the sea level fall. An alternative hypothesis was established to explain the stacking pattern of facies in M1 Sandstone. A tide-dominated delta with poor fluvial input experienced intense tidal erosion and produced a sharp base at the base of M1 Sandstone. Then subtidal sand bars, intertidal flats, and supratidal sediments were deposited in sequence during a continuous regression. The core and well logs in an extension of the study area in the northwest is interpreted as more distal open shelf deposits, beyond the mouth of the Tarapoa estuary system, where transgressive tidal shelf ridges were coeval with the Tarapoa estuary system. This interpretation allows us to predict the environment between the two areas as a transition zone between tide-dominated estuary and open shelf.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.