MATURITY INDICATOR AND GEOPORPHYRIN MEASUREMENTS USING A NOVEL ELECTRON PARAMAGNETIC RESONANCE SENSOR

Summary Electron paramagnetic resonance (EPR) sensor systems can detect free radicals and transitional metals in certain oxidation states, such as Mg2+, Mn2+, Co2+, Cu2+, Ni2+, Fe2+, and V2+. Measuring the concentration of free radicals in kerogen and asphaltenes can provide a new thermal maturity indicator for source rock and reservoir oil. Traditional EPR sensors use a resonant electromagnetic cavity and a permanent magnet for measurements, which limits the size of the detector to 10 cm. In this work, we demonstrate a newly designed EPR sensor without the traditional transmission resonant cavity. The new sensor, scale down to 2-3 cm, allows the maturity and geoporphyrin to be measured in borehole within a logging tool to provide in-situ and high resolution data.

Motivation and Results

A measurement on free radicals present in organic matter by EPR can be used as a maturity indicator for kerogen, bitumen and oil. An advantage of the EPR sensor is that it can be designed to respond to kerogen and bitumen present in source rock. We intend to package this device in a 3 cm OD tool for deploying it into a 1.5-inch logging tool. The new EPR logging tool would measure properties of source rock continuously in downhole, which may improve source rock evaluation by high-resolution data and help in sweet spots identification in shale reservoir.

Free radical concentrations for source rock and oil samples measured by the EPR sensor show good correlations with vitrinite reflectance and biomarker maturity, respectively. This is an important feature since other wireline measurements, such as resistivity, respond not only to kerogen/bitumen content, but also to resistivity changes in the inorganic parts within the source rock. Vanadyl porphyryins are quantified via the measurement of V2+ by EPR sensor on the samples. The sensitivity of the new EPR devices will be compared with the commercially available device. The EPR imaging by our new device has a spatial resolution of 0.3 mm and can be used for geochemical characterization of heterogeneous samples such as source rocks.