Effect of Oil Shale Processing on Water Compositions
This project is part of a larger water management effort in the Uinta Basin being performed at the Utah Geological Survey with the following objectives:
- Evaluation of saline water disposal problems impacting oil and natural gas development
- Examination of how saline water disposal from conventional petroleum development might create technical and economic hurdles for a prospective oil shale industry
- Collection of baseline surface- and ground-water information which could be used by oil shale development companies
- Analysis of water produced from different in situ oil shale extraction technologies (objective of this project)
Department of Energy, National Energy Technology Laboratory
All of the significant oil shale deposits in Utah are located in the Uinta Basin, a petroleum-rich basin that is home to significant conventional oil and gas production activities as seen in Figure 1. In the last few years, the basin has seen a large increase in unconventional gas production activity. In these operations, natural gas is produced from reservoirs of very low inherent permeability. One of the significant technical and environmental issues in these operations is the disposal of produced water. One method of disposing this water is to inject it into aquifers of sufficient capacity. Eastern Uinta Basin gas producers dispose of produced water in the Bird's-nest aquifer located in the Parachute Creek Member of the Green River Formation because of its suitability for large volume disposal. Utah's oil shale deposits are also located within the Parachute Creek Member. The Bird's-nest aquifer is typically several hundred feet above the richest oil shale interval, the Mahogany zone. In situ operations for the production of oil shale, which would require heating the deposits in place, could impact the dynamics of water movement and water composition in the aquifer and ongoing water injection activities.
Figure 1: Map showing proposed study area, Uinta Basin, Utah. Note that the prime oil shale area overlaps with several natural gas fields.
Researchers used the same experimental system constructed for another Institute for Clean and Secure Energy project, Multiscale Thermal Processes. Both hydrous and non-hydrous experiments were conducted. The analysis matrix included four water-phase and one oil-phase sample. The gas chromatography/mass spectrometry (GCMS) data obtained for volatile and semi-volatile hydrocarbons are compared in Table 1. Most of the targeted compounds, including the potential aromatics, are not in the detection limit of the instrument used. The C7-C35 aliphatic hydrocarbons were present in all the water-phase samples, and their amount increased with increase in pyrolysis temperature. The oil-phase sample shows a wide range of hydrocarbon species with the potential to be sources of contamination if in contact with water for a long duration. The GCMS analyses also revealed untargeted compounds like acid and alcohol groups.
Table 1: GCMS results for targeted volatile components.