Pore morphology effect on elastic and fluid flow properties in Bakken formation using rock physics modeling

Abstract: Unconventional geo-resources are critical due to their important contributions to energy production. In this energy transition and sustainability era, there is an increased focus on CO₂-enhanced oil recovery (CO₂-EOR) and geological CO₂ storage (GCS) in unconventional hydrocarbon reservoirs, and the extraction of hot fluid for energy through enhanced geothermal systems. However, these energy solutions can only be achieved through efficient stimulation to develop a complex fracture network and pore structure in the host rocks to extract heat and hydrocarbon, or for CO₂ storage. Using Bakken formation well data and rock physics models, this study aimed to identify the post-depositional effect of pore structure on seismic velocity, elastic moduli, and formation fluid; and further predict the best lithofacies interval for well landing, and the implications for fluid (gas, oil, and water) recovery in naturally- and often systematically-fractured geosystems. The KT and DEM models' predictions show distinct formation intervals exhibiting needle-like pores and having higher seismic velocities (V_p and V_s) and elastic moduli (K and µ), relative to other formation intervals that exhibit moldic pores. At the same fluid concentration, the needle-like pores (small aspect ratios) have a higher impact on elastic moduli, V_p, and V_s than on the moldic spherical pores with all other parameters held constant. V_p is affected more than V_s by the properties of the saturating fluid (gas, oil, or water) with V_p being greater in Bakken formation when it is water-saturated than when it is gas-saturated. V_s exhibit the reverse behavior, with V_s greater in the gas-saturated case than in the water-saturated case. Further, analyses suggest that the middle Bakken formation will have a higher susceptibility to fracturing and faulting, and hence will achieve greater fluid (oil and water) recovery. Our findings in this study provide insights that are relevant for fluid production and geo-storage in unconventional reservoirs. Article highlights: Integrated well log data and rock physics models.Investigated the effect of changes in pore structure on elastic properties and fluid flow in shale.Increase in porosity causes a reduction in elastic moduli and seismic velocities.V_p is more affected by pore geometry than V_s depending on density and properties of saturating fluid.Lithofacies with needle−like pores are more susceptible to fracturing than lithofacies with intragranular pores.