Date of Award
Master of Science (MS)
W.D. Gosnold Jr.
The factors that affect the subsurface temperature of a sedimentary basin were investigated by empirical and analytical methods. A review of thermal-mechanical models suggests that the Williston Basin was formed by more than one mechanism. The Williston Basin may have been initiated by a thermal event followed by thermo-flexural or phase transition subsidence.
The heat that initiated the formation of the Basin was significant to the thermal history of the Basin at its very beginning stage. However, most of the anomalous heat would have dissipated before the deposition of Bakken Formation 363 Ma ago. The heat flow history of the Basin was probably a steady-state condition after the Bakken was deposited.
Compaction is the major factor that affected the thermal structure of the Williston Basin after deposition of the Bakken Formation. Application of a decompaction scheme indicates higher paleotemperatures for the Williston Basin than would be calculated without decompaction.
Calculation of depth-porosity relationships for the Bakken Formation for four wells in the North Dakota portion of the Williston Basin shows a predictable correspondence between compaction and burial depths. The thickness of the Bakken Formation at each location changed proportionally with time as porosity decreased.
The decrease in porosity and thickness of the entire sedimentary section reduced the temperature of the rocks due to the increase in thermal conductivity and thinning of the thermal blanket.
The temperature history of the Bakken Formation shows a four-stage development. The different rates of temperature change reflect variations in rates of deposition and diagenesis of the overlying sediments. The temperature of the Bakken Shale increased slowly in its early history but rapidly in its late history.
Analysis of the thermal history of a sedimentary basin must consider the following: 1. time, temperature, and depth dependency of thermal conductivity 2. burial history 3. time-dependency in heat flow 4. surface temperature history
The time-temperature index (TTI) is an accurate measurement of thermal maturity if the above factors are included in the thermal history analysis.
Huang, Yue-Chain, "Thermal history model of the Williston Basin" (1988). Theses and Dissertations. 143.