Nuclear Magnetic Resonance Estimation of Petrophysical Properties and Evaluation of Hydrocarbon Huff-n-Puff Gas Injection in Lower Eagle Ford Shale Oil Samples

摘要

Shale oil formations are distinguished by the presence of kerogen and generated hydrocarbons (light oil & bitumen) occupying the organic and inorganic pores. This makes petrophysical measurements using conventional techniques very challenging. Moreover, implementing hydrocarbon gas huff-n-puff in shale oil formations as an improved oil recovery (IOR) method, although effective, creates a more complex system, where the underlying in-situ interactions are not fully understood. Nuclear magnetic resonance (NMR) measurements can predict fluid types occupying different pore sizes in a formation. As such, performing gas huff-n-puff in the laboratory on core and at the pilot scale in the formations can benefit from a non-destructive saturation measurement. This measurement can be used for the estimation of incremental oil recovery based on the initial oil-in-place (OIP). This study utilizes low field NMR relaxation measurements correlated with core analysis to estimate porosity, permeability and oil saturation properties of the Lower Eagle Ford (LEF) shale samples in the black-oil window and outline the in-situ rock-fluid interactions during the IOR process. NMR measurements of T2-relaxation and 2D T1–T2 maps are obtained for both outcrop and reservoir coreplugs in “as-received” and “fully-saturated” states, respectively. The outcrop plug is saturated with hexadecane, while the reservoir cores are saturated with produced oil from the Eagle Ford formation at different temperatures (40°C and 125°C) and a pore pressures of 3500 psi. The pressure of 3,500 psi was chosen because it is ~800 psi above the bubble point of the reservoir fluid and provides for a pressure drop to occur for the puff cycle. Saturation measurements are developed for the LEF shale oil core plugs for which the efficiency of the gas huff-n-puff IOR technique is evaluated. On the other hand, subsequent NMR measurements were acquired after conducting hydrocarbon gas huff-n-puff recovery on both the outcrop and reservoir core plugs in a high temperature, high pressure (HTHP) system at optimum cycles. Produced hydrocarbon is estimated by calibrating NMR data with mass balance measurements.