Type of Thesis
Four recent discoveries in the Upper Jurassic eolian Norphlet reservoirs in the northeastern deepwater Gulf of Mexico have resulted in a new petroleum play in water depths greater than 7,500 feet. This new play has many similarities to onshore and shelf regions of the Norphlet play. Analyses of logs from 26 wells, mud logs, biostratigraphy, and 500 km of 2D seismic help to evaluate the stratigraphic evolution and thermal maturity of the area.
The Upper Jurassic strata record the initial transgression in the Gulf of Mexico after continental breakup and early ocean spreading. After deposition of the Louann salt in syn-rift grabens (Callovian), the Norphlet eolian system (early Oxfordian) was deposited on and between the salt pillows. These strata were transgressed by the Smackover, a shallow marine limestone. A marl unit in the upper Smackover is interpreted to be the source rock for the Norphlet oils. The Haynesville Formation (Kimmeridgian-early Tithonian) overlies the Smackover, and consists of shallow marine marls and limestones. Deposited in deepening waters, the Cotton Valley Formation is primarily a shallow marine shale unit, with occasional storm and small progradational deposits. The primary source rock in the northern Gulf of Mexico was deposited near the top of the Tithonian.
Deposition of these Upper Jurassic strata were strongly controlled by active tectonism. The Middle Ground Arch, a NE trending basement-high, segmented the Norphlet into an eolian facies to the north, and a mixed eolian fluvial-overbank setting to the south. During the Kimmeridgian, salt rafts developed and began to translate basinward (southwest) creating differential accommodation for the Haynesville and Cotton Valley strata. As a result, expulsion rollovers formed, creating basinward thickening wedges that downlapped onto the decollement within the fault gaps of the rafts. Today, a series of isolated rafts are present in the area; all of the traps in the four discoveries developed in association with the formation of the rafts.
The thermal maturity and potential of the two Jurassic source rocks were evaluated using well log techniques. The upper Oxfordian limestone and marls of the Smackover did not indicate substantial potential in the Delta R evaluation. In contrast, the upper Tithonian section shows good Delta R separation, indicating high TOCs. The resistivity response for both source rocks is muted, indicating oil generation in the early oil window.
Payeur, Travis, "Sequence Stratigraphy and Source Rock Evaluation of Jurassic Units, Northeastern Deepwater Gulf of Mexico" (2016). Undergraduate Honors Theses. 1249.
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