Douglas H. Loose

Accurate Volumetric Flow Rate and Density Based Water-Cut Measurement in Bubbly Liquid Hydrocarbon Flow

Oil and gas production is inherently multiphase. A significant cost of production is directed toward accurately measuring and allocating produced hydrocarbons. The presence of gas phase in liquid flow impairs accurate measurement, introducing errors in well and field production allocation. These errors distort the reservoir engineer production information and directly affect the fiscal allocation from multiple owners. A SONAR-based system to measure the gas void fraction (GVF) next to turbine and Coriolis meters is proposed as a method to correct for gas bubbles. A test was conducted at Southwest Research Institute (SwRI) to validate this concept on realistic multiphase fluids. The SwRI test was designed to simulate separator liquid out-flow conditions and to assess the ability of GVF measurement to correct for the errors introduced by entrained gas in turbine and Coriolis meters. The data show that both the turbine and Coriolis meters over-report the volumetric flow rate in proportion to the amount of entrained gas. Using a GVF measurement provides a simple correction to the primary measurement of both meter types to within ±1% of the reference liquid flow rate for 0-8% GVF. The Coriolis meter correctly measured the mixture (liquid + gas) density within ±1% of the reference, independent of entrained gas levels. The liquid density is required to determine water-cut and in this test it was calculated by correcting the measured mixture density for GVF. Using a simple GVF correction, the liquid density was reported to within ±1% for 0-10% GVF. An accurate measure of liquid hydrocarbon volumetric flow rate and density independent of the amount of entrained gas can be achieved using turbine and Coriolis meters in conjunction with a SONAR-based GVF measurement. This capability enables improved reservoir management as well as increased separator design flexibility, reducing complexity, cost and weight.

Application of Novel Speed-of-Sound Based Technique to Measure Steam Wetness With Potential Application Into LP Exhaust

Wet steam is a common occurrence at the exhaust of the LP turbines in fossil-fired steam plants. In nuclear turbines, wet steam will be found right from the high-pressure sections. The presence of moisture in steam reduces the aerodynamic efficiency of the turbine sections, thus reducing the overall efficiency of the turbine. Additionally, water droplets also cause erosion and corrosion of buckets and other components. LP turbines account for a significant portion of the total cost of the turbines (due to the enormous sizes required by the expanding steam) and produce significant portion of the power output. Measuring and controlling wetness will help improve both the performance and reliability of turbines. A novel way of measuring the composition of wet steam using a speed of sound based technique is being developed. The technique, based on technology developed for measuring two-phase flow compositions in down-hole (oil-field) applications, relies on measuring acoustic pressures propagating in a one-dimensional wave-guide (pipe or tube) using an array of axially located pressure transducers. The technique is non-intrusive to the flow field and relies on passive listening of the noise generated by the flow itself (and, hence differs from the conventional ultrasound based techniques). The current study is an ongoing effort and the paper will focus on the feasibility of this technique for wet steam application. The eventual aim is to be able to measure steam wetness in the range of 0–10% with an accuracy of ± 0.2%. Initially, the ability of the technique to accurately measure the wetness in air-water mixture was established using an air and water mist facility. Next, high subsonic flow conditions were evaluated in single phase (air only) flow using a wind tunnel facility. Excellent agreement between speed of sound calculated for air, based on conventional pressure and temperature measurements in a wind tunnel, and that measured directly by the probe was obtained. The wind tunnel tests showed that the SOS measured by the probe and conventional instrumentation agreed within ± 1.5%. This establishes that the technique is capable of accurately measuring the speed of sound, which is the primary variable to calculate the flow composition. The technique can also be used to measure volume. Although the wind tunnel tests were not specifically designed to assess the accuracy of the flow rate measurement, comparisons were made between the flow velocities given by the probe and reference measurements. The additional motivation was to assess the ability of the probe to monitor volume flow/mass flow at high Mach numbers where only shorter straight sections are available. The flow velocities measured by the probe agreed with those calculated using the wind tunnel instrumentation (wall-static taps) within the estimated uncertainty levels introduced by the flow blockage and profile distortions. Additional tests are planned to assess flow rate accuracy. Effort is continuing to study steam flows representative of exhaust of low pressure steam turbines in steam plants.Copyright