Change of Bakken Shale Stiffness Due to CO2 Saturation

Ogochukwu, Ozotta, University of North Dakota, ogochukwu.ozotta@und.edu; Mehdi Ostadhassan, mehdi.ostad- hassan@gmail.com; Kouqi Liu, liu3k@cmich.edu (Poster)

Middle-Bakken is a heterogeneous material with complex microstructures, lithofacies and mineralogical composition. To evaluate the mechanical properties of the rock material and the volume fraction, mineral composition is a critical factor because rock brittleness index increases with increase of the brittle mineral content in the rock with minerals like calcite, sulfur, and zinc-blend. Major minerals present in the Middle-Bakken include clay, calcite, quartz, dolomite, and feldspar. Minerals present in the Middle-Bakken sample at the depth of investigation are calcite, quartz, dolomite, plagioclase, pyrite, and halite. Calcite dissolution is more common in carbonate-rich rock and it increases the brittleness of the rock and makes it susceptible to fracture, whereas precipitation of clay minerals as calcite dissolves make the rock more ductile and susceptible to deformation. The minerals present were estimated from the Field Emission Scanning Electron Microscope (FE-SEM) image. The sample was exposure to CO2 for up to 60 days and the elastic properties of the mineral grains in the Middle-Bakken was measured using nanoindenation testing. Statistical Approach was used to interpret the changes in the mechanical properties of the mineral grains and the changes in the volume fraction of the minerals before and after CO2 saturation, and general decrease greater than 40% was observed. Frequency distribution showed the volume concentration of the minerals based on their elastic properties as it changes from pre-saturation to post-saturation. Discrete distribution map was used to visualize the spatial distribution of the individual mineral grains present in the rock. The discrete distribution map shows the elastic modulus and hardness of the shale reservoir for CO2 pre-saturation and for post-saturation periods. A heterogeneous distribution of both mechanical properties in the shale reservoir was observed. The images roughly display the microstructure morphology of tested area and then indicate the approximate surface fraction of different constituent phases.

Bio:

Ogochukwu Ozotta is a PhD candidate in petroleum engineering at the University of North Dakota (UND). She works as Graduate Geophysics Research Assistant at the UND Energy & Environmental Research Center (EERC), Grand Forks, North Dakota, USA. She conducts research focused on geologic storage of CO₂, including geologic model construction, well log analyses, seismic data interpretation, seismic geomechanics, fluid substitution modeling, reservoir simulation, geomechanical analyses, rock physics, and assessment of enhanced oil recovery potential. 

She is currently in her second year where she is analyzing the impact of CO₂ injection on the geomechanical and geophysical properties of the unconventional Bakken Formation and the potential for fault reactivation in the Williston Basin. 

She started chapters for the Association for Women Geosciences (AWG) Williston Basin Chapter and the Graduate Women in Science (GWIS) in Grand Forks, ND alongside others. She serves as the Vice-President (Eastern) North Dakota Geological Society. Ogochukwu loves to travel, listen to classic music, and try new recipes.

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