Shallow surface thermogenic hydrocarbon migration over western Prudhoe Bay Region, Alaska

Sarkar, Sudipta

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Abstract

"Hydrocarbons leak from petroleum reservoirs to the surface. In continuous permafrost regions like the Alaska North Slope, surface migration of thermogenic hydrocarbons may be hindered by the presence of ground ice. However, suitable permeable migration pathways in the permafrost can exist. Unfrozen sediments at the bottom of the lakes, or open faults can facilitate thermogenic hydrocarbon migration. I studied the nature and distribution of gaseous alkanes (C1 to C6) and helium in the shallow permafrost cores (2 m depth); depth profiles of alkanes (C1 to C7) in the two wells (1500 m deep); and stable isotopes of CH₄ trapped in lake gas bubbles, to trace the presence of thermogenic hydrocarbons and their migration pathways. Geostatistical analysis of the alkane and helium distributions shows that most anomalies occur along northwest-southeast oriented lineaments, roughly corresponding to the trend of the Eileen fault mapped at 2675 m depth, high fault density zones of the Kuparuk Formation, and northwest-southeast trending Sagavanirktok faults mapped at 457 m depth. The anomalies above the Eileen fault can be explained by a fluid-flow model in a dilational jog along a wrench fault. This model agrees with the movements along the Eileen fault"--Leaf iii

Description

Thesis (M.S.) University of Alaska Fairbanks, 2008

1. Introduction -- 1.1. Problem definition -- 1.2. Hypothesis -- 1.3. Objectives -- 2. Background -- 2.1. Geological background -- 2.1.1. Stratigraphy -- 2.2. Petroleum reservoirs -- 2.2.1. Kuparuk petroleum reservoir -- 2.2.2. Prudhoe Bay reservoir --2.2.3. West Sak reservoir -- 2.2.4. Petroleum filling history and hydrocarbon migration -- 2.3. Permafrost geology -- 2.4. Gas hydrates -- 2.5. Concept of hydrocarbon generation and migration -- 2.6. Helium in soil gas -- 2.7. Soil interference -- 3. Data -- 3.1. Soil hydrocarbon gas data -- 3.1.1. Sampling -- 3.1.2. Sample analysis -- 3.2. Lake gas data -- 3.2.1. Sampling -- 3.2.2. Sample analysis -- 3.3. Geochemical data from exploration well -- 3.3.1. Sampling -- 3.3.2. Sample analysis -- 3.4. Structural data -- 3.4.1. Fault maps -- 3.5. Satellite imagery -- 4. Methodology -- 4.1. Data processing -- 4.2. Data analysis -- 4.2.1. Statistical analysis of gaseous hydrocarbon data -- 4.2.1.1. Exploratory data analysis (EDA) -- 4.2.1.2. Detection of hydrocarbon anomalies -- 4.2.1.3. Semivariogram analysis -- 4.2.1.4. Structural analysis with semivariogram -- 4.2.2. Analysis of hydrocarbon concentration data in soil gas -- 4.2.2.1. Pixler diagram -- 4.2.2.2. Bernard ratio (R) -- 4.2.2.3. Wetness percent -- 4.2.3. Genetic classification of soil gas data using CH₄ stable isotopes -- 4.2.3.1. Analysis of stable carbon isotope of CH₄ and CO₂ -- 5. Results -- 5.1. Results of statistical analysis with 1991 soil hydrocarbon gas data --5.1.1. Exploratory data analysis results -- 5.1.2. Statistical determination of hydrocarbon and helium anomalies -- 5.1.3. Semivariogram analysis -- 5.1.4. Genetic classification based on Pixler diagram -- 5.1.5. 1991 soil gas anomaly maps -- 5.2. 1992 winter soil hydrocarbon gas analysis -- 5.2.1. Gas samples with only hydrocarbon compositional data -- 5.2.2. Gas samples with both stable isotope isotope and compositional data -- 5.3. Lake gas analysis -- 5.4. Geochemical profiles from exploration well data -- 5.4.1. Geochemical profiles of hydrocarbon gases in KRU 2D-15 -- 5.4.2. Geochemical profiles of hydrocarbon gases in PBU R-01 -- 6. Discussion -- 6.1. Hydrocarbon migration through faults -- 6.2. Geostatistical correlation between faults and surface anomalies -- 6.3. Sources of surface hydrocarbon gas -- 6.4. Vertical hydrocarbon migration -- 6.5. Subsurface sources of hydrocarbon gases -- 7. Conclusions -- References cited -- Appendix.

Date

2008-12

Type

Thesis

Collections

Geosciences