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.