The Application of Gamma Ray Computer Tomography to Oil Recovery Studies

During the last two years work has been published(1,2)in which medical X-ray CT Scanners were used to study the flow of fluids through rock cores in order to improve the understanding of flow processes occurring within oil reservoirs. Whilst such experiments provide a valuable qualitative insight we believe that the use of isotopic ɣ-rays, which are practically monoenergetic compared to the output of even filtered X-ray tubes, offers several advantages. In principle all measurements become absolute, in that results are repeatable and machine independent (unlike X-ray CT scanners) and since the results are quantitative, estimates of confidence limits are easily made. Monochromatic ɣ-rays do not suffer from beam hardening and radioactive sources also offer advantages in terms of cost, compactness and a well defined variation of output intensity with time - ie. exponential decay. However, the photon output may be nearly four orders of magnitude lower than that from an X-ray tube and so current scan times are ~3000 s for a single beam arrangement. It is unlikely that moving to multiple (ie fan) beams will reduce this by more than a factor of ~30 and hence it is improbable that very rapid measurements on dynamic systems with time scales below 100 s will ever be feasible.