Detecting Asphaltenes by A Miniaturized EPR Sensor
Authors: Yang X. , Tavakkoli M. , Chapman W. , Babakhani A. 
Published: March 2015

Abstract
Asphaltenes precipitation has become a major issue in oil production. It can clog oil wells and increase the cost of production. The precipitation can occur in the near-wellbore region, inside the wellbore, in subsea flowlines, and in the separator. Currently, there is no effective solution for monitoring asphaltenes concentration and precipitation in real time. In this work, we propose a novel method for monitoring asphaltenes concentration in crude oil, utilizing the physical principle of Electron Paramagnetic Resonance (EPR). The phenomenon of EPR is based on the interaction of electron spins with electromagnetic fields in the presence of an external DC magnetic field. As asphaltenes have paramagnetic centers, they generate EPR signals that can be measured with our proprietary EPR sensor. The sensor is implemented in a 0.13µm SiGe BiCMOS process technology. The sensor chip can operate in both continuous wave (CW) and pulse modes. The frequency is tunable from 770MHz to 970MHz, corresponding to Zeeman magnetic fields from 28mT to 35mT for a free electron. The chip consists of a voltage-controlled oscillator, a power amplifier, a low-noise amplifier, a down-conversion mixer, baseband amplifiers, and a pulse generation block. The EPR sensor uses a loop-gap resonator built on a PCB board to interact with the sample. The measurement results of the asphaltenes samples are reported.

1. Introduction
Asphaltenes are among the most complex components in crude oil. They are commonly defined as hydrocarbon-based materials that are toluene soluble and n-heptane insoluble [1]. In oil production, for a long time, asphaltenes deposit removal has been remained a major challenge. Asphaltenes percipitation can clog oil pipelines, thereby imposing strong and negative impacts on production [2]. In order to effectively and timely mitigate the effects of asphaltenes precipitation, the asphaltenes concentration in the crude oil must be monitored in real time. Unfortunately, no practical solution exists to achive this goal. In this work, we propose a novel monitoring method that can detect the asphaltenes concentration in crude oil in real time, utilizing the physical principle of Electron Paramagnetic Resonance (EPR). Asphaltenes contain unpaired electrons, which produce EPR signal that can be measured using conventional EPR sensors [3]. However, existing EPR sensors comprise components that are expensive, heavy, and large, which prevent their use in real-time flow-assurance applications. In this work, for the first time, we have used advanced integrated circuit (IC) technology to implement an EPR transceiver on a chip smaller than 4mm2. Measurement results show that the sensors can effectively detect asphaltenes extracted from crude oil.

2. Electron Paramagnetic Resonance (EPR)
EPR phenomenon is based on the interaction of electron spins with electromagnetic fields in the presence of an external DC magnetic field [4]. EPR data provides valuable information about electronic structures and spin interactions in paramagnetic materials. The EPR data of a sample can be measured using an EPR sensor, which typically consists of the following major components: transceiver circuits, a magnet with adjustable magnetic field, and a resonator.