Accurate Water-Cut Measurement for Thermal Operations
Presented at the ISA Calgary Show, April 23, 2015.
Measurement of the water-cut (the water fraction) of the produced emulsion is necessary for oil producers in determining their daily oil production. Typically water-cuts are routinely measured by manual sampling of the emulsion and then analyzed by methods which may include spinning the sample in a centrifuge onsite to separate the oil from water, or sending the samples to a commercial lab. Magnetic resonance (MR) technology has been applied to address this problem and it has advantages over other existing technologies. MR is a well-established technology in chemical and medical applications. When applied to analyze oil and emulsions with water, it has proven to be fast, reliable and accurate, compared to Dean-Stark analysis, for determining water-cut. MR has been incorporated into the design of an online instrument to measure water-cut in produced oil-water emulsion streams. This technology is insensitive to changes in salinity of the fluids, which is a problem for other technologies in measuring water-cuts. The instrument described in this paper operates on a slipstream, or by-pass, of flow of the produced emulsion that is taken off a main flow line. For a given MR measurement the flow in the by-pass loop is held stationary for the measurement which takes about 2 minutes. The heart of the instrument employs a non-intrusive electrical coil and a permanent magnet surrounding the instrument pipe. Magnetic Resonance technology detects electro-magnetic signals from both the water and the oil components in the fluid. The main advantages of the MR water-cut meter are: i) relatively fast (2 minutes to measure) and accurate water-cuts near the well head, ii) high frequency of measurement (every 5 minutes) on a continuous basis without the need for manual sample collection, iii) ability to monitor directly the water, oil and gas fractions in the production stream.