Erling Hammer

Recent developments in three-phase flow measurement

The problem of how to meter oil - water - gas mixtures has been a significant one in the oil industry since the early 1980s. Since then, considerable research has been conducted into the development of a three-phase flowmeter suitable for use in an offshore environment. This work discusses why three-phase flow measurement is important, the principal strategies and technologies which may be used to meter three-phase flows, and reviews the status of some currently available solutions.

Capacitance sensor design for reducing errors in phase concentration measurements

Abstract A capacitance sensor configuration which can measure the water fraction and undissolved gas in crude oils with higher accuracy than currently available non-intrusive capacitance sensors has been studied. In this sensor the surface electrodes are helical so that the electrical field is twisted 180° or 360° from one end of the sensor to the other. This sensor has been investigated in detail by means of a three-dimensional capacitance model based on Poissons equation. The model is based on the “Finite Element Method” (FEM). This model enabled us to simulate the capacitance of the helical sensors as a function of changes in flow parameters, including water fraction, void fraction, permittivity and distribution of the flow components and changes in sensor geometry and design such as length of the sensor, type of guard electrode, thickness and permittivity of the electrode insulation layer (liner), diameter of sensor screen, etc. The model was verified against measurements on different types of sensors and flow regimes, and the maximum difference between simulated and measured results was ±5%. The mathematical model was used to optimize the design of the helical surface plate capacitance sensor with respect to sensitivity, accuracy and flow regime independency. Our simulations show that by using helical surface electrodes the overall accuracy is estimated to be within ±0.4% for gas/oil mixtures and ±5% for oil–continuous water/oil mixtures of full scale.

Capacitance Transducers for Non-intrusive Measurement of Water in Crude Oil

Capacitance transducers used to measure the water content in crude oil have attracted a great deal of interest because of their fast dynamic response and the possibility of constructing them as non-intrusive, in line, full bore sensors covering the whole main pipe cross section. Inaccuracies due to sampling error will thus be avoided, but error caused by changes in flow regime, salinity of the water component, inhomogenety of the electric field between the electrodes, spread capacitances etc. will still influence the measurement results. To minimize these influences it is of great importance to know the basic theory which underlies this technique. The water-in-oil monitor has been tested by Connocos research and development department in Ponca City and by Norsk Hydro. The accuracy is 1.5% water. A non-intrusive, full bore, water-in-oil monitor has been developed which significantly extends the range of water contents measurable (0 to 80% v/v). By incorporating helical electrodes dependence on variation in flow regime can be reduced. Laboratory tests of this precision water-in-oil monitor indicates that an accuracy of 0.05% v/v water fraction can be obtained.

Multimodality tomography for multiphase hydrocarbon flow measurements

Multimodality sensing is used for monitoring of multiphase hydrocarbon flow where there is a need to measure the quantity of oil, water and gas in a cross section of a pipe originating from an oil well. Information on the flow regime, i.e., the physical distribution of the hydrocarbon production constituents in the pipe cross section, is demanded. Expedient information concerning the productivity of the well, i.e., the quantity of oil, water and gas produced, the transport of multiphase flow and the upstream separation process can be provided by tomographic information. A dual modality tomograph (DMT), consisting of capacitance and gamma-ray sensors, has been developed at the University of Bergen. Characterization of the DMT has demonstrated feasibility in relation to the hydrocarbon flow application, but also shortcomings mainly relating to the performance of the capacitance sensor in water continuous phase, and the salinity dependence of the gamma-ray measurements. Research work has been conducted to further develop the DMT for hydrocarbon multiphase flow. The new developments include dual modality densitometry (DMD), where both mixture density and salinity are measured, and a water-cut independent high-frequency magnetic field sensor.

Process Tomography in the Oil Industry — State of the Art and Future Possibilities

The use of tomographic techniques has long traditions within the oil industry. The primary application has been for exploration and characterization of oil and gas reservoirs. Various seismic methods have been applied: Surface surveying, reversed vertical profiling, crosswell reflection imaging and crosswell tomography!. For the latter, which implies the use of downhole transmitters (sources) and receivers in two or several neighbour wells, electromagnetic tomography is also being developed2.3 • Parameters of concern are porosity, pore fluid type and saturation. Tomographic methods have also been used for laboratory studies of rock samples (cores) obtained from oil and gas reservoirs, with applications both in the area of core analysis and petrophysics as well as multiphase flow. The latter is related to displacement studies giving insight into problems such as viscous fingering, gravity segregation and mobility control. These are all important input parameters in reservoir modelling and simulation where one of the ultimate goals is enhanced oil recovery. X-ray CT (Computed Tomography)4.5.6.7 and microtomograph y8, gamma-ray tomography9.lo, Nuclear Magnetic Resonance Imaging (MRI) 11, electrical resistance tomography l2 and ultrasound mapping have been applied for these purposes. These are all methods to optimize production and utilization of gas and oil wells which is increasingly important as petroleum resources are finite and becoming even more elusive. This also introduces a trend shift within petroleum production where new methods allow profitable utilization of marginal wells and wells with high water cut (water content). One of the consequences is a need of more accurate instrumentation for flow measurement, e.g. for allocation purposes, and process control. These are applications where the term process tomography primarily applies.

High-frequency magnetic field probe for determination of interface levels in separation tanks

There are many principles for interface level detection in separation tanks based on capacitance, ultra sound, microwave, nuclear radiation etc. These principles work well in many situations, in others they fail. The high frequency magnetic field principle works in most of the situations that will occur in separation tanks for crude oils for detection of the clean water level, the layers of water continuous water/oil emulsion and the oil continuous oil/water emulsion, the oil level, the thickness of the foam layer and the gas. When a coil is dipped into a fluid its electrical impedance will be dependent on the characteristics of the fluid. If the material is electrical conductive the impedance of the coil will be reduced due to the eddy currents induced in the material, setting up a magnetic field directed against the field generated by the coil. The inductance will increase but still remain low also in the water continuous water/oil emulsion zone, but will rapidly increase in the oil continuous oil/water emulsion zone. In pure crude oil the inductance will be high and even higher in gas. The coil inductance is measured by connecting the coil to a LC-oscillator.