Thermal oil recovery factors from sandpacks of variable mineralogy

Abstract

Steam injection is commonly used for production of viscous crude oil. Reservoir rock often contains clay minerals. Reactive nature of steam and clay minerals may lead to formation damage. This work investigates oil recovery and changes in petrophysical properties as a function of the mineralogy. Sandpacks with quartz, calcite, feldspar, kaolinite, smectite, and illite were prepared for steam injection experiments. Permeability of the steamed sandpacks was determined using coreflood experiments. Chemical composition of the produced aqueous samples was determined using ICP-OES (inductively coupled plasma-optical emission spectroscopy). Morphology of the rock samples was studied using SEM-EDS (scanning electron microscope-energy dispersive X-ray spectroscopy). Mineralogy and elemental content of the solid samples were determined using XRD (X-ray diffraction) analysis and XRF (X-ray fluorescence) respectively. It was found that aqueous phase samples produced from clay-rich sandpacks tend to have higher pH than samples produced from samples without clay minerals. Oil recovery factors for 100% quartz case was determined to be 65 wt%. Calcite- and feldspar-rich sandpacks produced 56 and 61 wt% of oil respectively. Sandpacks with clay fractions have shown the lowest oil recovery – 39, 29, and 28 wt% for kaolinite-, smectite-, and illite-rich samples respectively. Mineral dissolution and precipitation were the dominant damaging mechanism for quartz and calcite cases. Feldspar-rich sandpack demonstrated signs of structural destruction of the mineral and fines release. Kaolinite's effect on oil recovery was found to be associated with fines migration. Smectite hydration and swelling in presence of steam was the dominant formation damage effect on the oil production. Steam interaction with illite-rich sandpack caused formation of amorphous silica. This paper presents oil recovery factors as a function of injected pore volume (PV) of steam for sandpacks of different mineralogy. Obtained results characterize petrophysical changes caused by steam interaction with minerals in presence of oil. This data provides insights into effects of steam on minerals with different structures and properties.