Isotopic Insights into Water of Condensation, Cross-Formation Water Flow, and Natural Hydrocarbon Migration in Sedimentary Basins
This dissertation applies geochemical tools to track the movement, transformation, and behavior of water and gases in hydrocarbon-bearing sedimentary basins. During petroleum exploration and production, hydrocarbons are generated at the surface along with other fluids naturally present in the formation, such as formation water. In addition, where hydraulic fracturing is used to stimulate shale gas and oil production, a percentage of the injected fracturing fluid also returns to the surface. Understanding the origin and movement of these water sources, as well as targeted and non-targeted hydrocarbon gases is critical to evaluating reservoir performance and properly managing fluids at the surface. However, tracking fluid migration in deep sedimentary basins is not a simple task, as it can be significantly affected by geologic, chemical, microbial, and anthropogenic processes. This dissertation provides a framework for evaluating three types of fluid occurrence or movement that can affect our interpretation of fluid origin during hydrocarbon production: 1) Identification of water condensing out of the gas phase (i.e., water of condensation) as a potentially significant component of produced water from shale gas wells. 2) Detection of recent cross-formation flow of deep formation waters; and 3) Distinguishing between gas seepage at the surface due to natural pathways (i.e., natural seeps) vs. anthropogenic pathways. In the first study, I show that isotopes of water, in concert with salinity, can be utilized to identify water of condensation as a source of fluid in produced water from Marcellus shale gas wells in the Appalachian Basin. In the second study, I utilize a combination of 228Ra/226Ra and 87Sr/86Sr ratios to identify recent cross-formation flow that is supplying “out-of-zone” water into Marcellus shale gas wells. My third study presents a strategy for the application of isotopic and molecular methods to distinguish between naturally seeping hydrocarbon gases (and associated water, where present) and anthropogenic releases in hydrocarbon-bearing basins throughout California. Collectively, these approaches hold promise for unraveling water and gas origin and chemistry in a variety of settings within hydrocarbon-bearing basins.
Geochemistry|Sedimentary Geology|Petroleum Geology
Molofsky, Lisa J, "Isotopic Insights into Water of Condensation, Cross-Formation Water Flow, and Natural Hydrocarbon Migration in Sedimentary Basins" (2023). ETD Collection for University of Texas, El Paso. AAI30494353.