Compositional Controls on Micro-Scale Fluid Distribution in Tight Rocks: Examples from the Montney Formation (Canada)
- David Cronkwright (University of Calgary) | Amin Ghanizadeh (University of Calgary) | Chris DeBuhr (University of Calgary) | Chengyao Song (University of Calgary) | Hanford Deglint (University of Calgary) | Chris Clarkson (University of Calgary) | Omid Ardakani (Geological Survey of Canada)
- Document ID
- Unconventional Resources Technology Conference
- SPE/AAPG/SEG Unconventional Resources Technology Conference, 22-24 July, Denver, Colorado, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. Unconventional Resources Technology Conference
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- 68 since 2007
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Fluid distribution and fluid-rock interactions within the nano-/macro-porous pore network of tight oil reservoirs will affect both primary and enhanced oil recovery (EOR) processes. Focusing on selected samples obtained from the liquids-rich reservoirs within the Montney Formation (Canada), the primary objective of this work is to evaluate the impact of mineralogical composition on micro-scale fluid distribution at different saturation states: 1) “partially-preserved” and 2) after a series of core-flooding experiments using reservoir fluids (oil, brine) under “in-situ” stress conditions.
Small rock chips (cm-sized), sub-sampled from “partially-preserved” (using dry ice) core plugs, were cryogenically frozen and analyzed using an environmental field emission scanning electron microscope (E-FESEM) equipped with X-ray mapping capability (EDS). For a core plug subjected to core-flooding and subsequent cryogenic preservation, three sub-samples were taken, representing the upstream, midstream, and downstream portions of the core plug sample. Images were acquired at various magnifications and analyzed using multiple image analysis techniques to identify 1) fluid type (oil, brine), 2) mineral grain composition, and 3) the contact length/area between occupying fluids and mineral grains. Additionally, for selected “partially-preserved” samples, sub-samples were obtained and subjected to different stages of a modified Rock-Eval technique (i.e. extended slow heating (ESH) Rock-Eval) to differentiate free hydrocarbon phases from (solid) organic matter through thermal pyrolysis.
For “partially-preserved” samples, this study demonstrates that the combination of cryo-SEM/EDS and thermal pyrolysis techniques can be used as an effective tool to visualize changes to pore-filling light free hydrocarbons, heavy fluid-like hydrocarbon residue (FHR), and solid organic matter (i.e. bitumen). For core-flooding experiments (brine injection into oil-saturated core plug) combined with cryo-SEM/EDS techniques, this study demonstrates that compositional controls on micro-scale fluid distribution can be quantified effectively. Providing examples from the Montney Formation, the latter experimental observations indicate that 1) oil-filled pores are more abundant at the downstream end, 2) brine is increasingly associated with dolomite- and pyrite-lined pores, and decreasingly associated with feldspar- and quartz-lined pores moving towards the downstream end of the core plug, and 3) residual oil saturation appears to increase with clay content throughout the length of core plug.
The understanding of pore-scale fluid distribution and fluid-rock interactions are critical for identifying controls on primary and enhanced oil recovery processes in tight oil reservoirs. Through application of multiple experimental (e.g. cryo-SEM/EDS, ESH Rock-Eval, core-flooding) and image analysis techniques, this study provides valuable insight into the micro-scale compositional controls on “in-situ” fluid distribution in tight siltstone reservoirs such as the Montney.
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