LAUSR

Abstract High original oil-in-place estimates accompanied by low primary recovery potential of organic-rich shale formations make them suitable candidates for enhanced oil recovery (EOR) projects. The organic-rich shale formation under investigation in this paper is the Bakken shale formation that exhibits significant variations in lithology, rock texture, clay content, porosity, and total organic carbon (TOC). Three wireline-log-derived EOR-efficiency indices are generated across the 200-feet-thick Upper, Middle, and Lower Bakken formations to identify flow units suitable for EOR using light, miscible hydrocarbon injection. R-index is one of the three EOR-efficiency indices. R-index is calculated using kerogen content, water saturation, permeability, principal pore throat diameter, and porosity. Microscopic Displacement (MD) Index computes the microscopic displacement efficiency for the miscible gas injection. An important step in computing MD-index is to decompose NMR T2 distribution at each depth using factor analysis to compute the free oil, movable water, and bound fluid volumes. Moreover, the MD-index accounts for the effect of pore confinement on miscible oil volume and the effect kerogen content on the displacement efficiency. MD-index relies on a novel method to calculate the miscible free-oil volume from subsurface NMR T2-distribution logs. Lastly, k-means clustering method was used to generate the third index, referred as the KC-index, which is in the form of a step-wise curve. KC-index partitions the entire formation into four groups, representing miscible-gas-injection recovery potentials at discrete levels. The method uses water saturation, porosity, permeability, bound fluid volume, and principal pore throat diameter derived from various logs. The proposed log-derived EOR-efficiency indices generate consistent predictions of miscible light-hydrocarbon injection performance in the Bakken shale formation at various resolutions. Indices indicate that several formation zones in the middle section of the formation will have much higher recovery potential in comparison to the upper and lower sections of the formation. At a resolution of 1-foot depth interval, several flow units were successfully identified in the middle section that exhibit high miscible-gas-injection recovery potential.