Research On Fluid Recoverability Of Reservoirs Based On NMR Technology

It is very necessary to evaluate the fluid recoverability for the development potential of low permeability oilfield. Especially, in recent years, the main development target is extra-low permeability oilfield and tight oilfield, the fluid mobilization evaluation seems much more important. A mass of works about the percentage of movable fluid testing by NMR technology have been done, but the main works focused on parameter testing of movable fluid, and not have been formed a systematic method of fluid recoverability evaluation.Many experiments about fluid recoverability have been conducted by using the method of NMR, conventional mercury injection and centrifugation. The results indicate that the mean value of movable fluid saturation is 28.04%,49.72% and 63.38% respectively. Besides, for the tight formation, the main distribution interval of movable fluid is less than 0.20μm.The movable fluid of extra-low permeability reservoir is mainly controlled by throat from 0.10μm to 0.50μm.The movable fluid of ultra-low permeability reservoir is mainly controlled by throat bigger than 0.50μm. Compared with tight formation and extra-low permeability reservoir, the movable fluid of ultra-low permeability reservoir is mainly controlled by big throat.Meticulous research has been done between movable fluid and micro-pore structure. The relationships between movable fluid saturation and uniformity coefficient, sorting coefficient, structure coefficient, maximum throat radius, and mean throat radius have been analyzed. The result indicates that the relativity between the movable fluid saturation and throat radius is the best. The value of initial oil saturation is often bigger than its actual value tested by mercury injection capillary pressure curve. In order to analyze the reason, the percentage of movable fluid and percentage of mercury injection volume of different interval of throat radius have been analyzed. The result is that the saturation of mercury injection is bigger than the saturation of movable fluid of ultra-low permeability reservoirs, and the bigger section is focused on throat with radius of less than 0.50p.m. So, for the ultra-low permeability reservoirs, it is necessary to combine the NMR technology and mercury injection capillary pressure curve for accurate initial oil saturation test.New method of movable oil saturation test based on NMR technology has been exploratory presented. Combining with NMR technology, the movable oil saturation can be tested more accurately by the experiment of water-flooding and oil driving water centrifugation. The process of oil driving water simulate the process of oil reservoir formation, and the process of water driving oil simulate can indicate the characteristic of oilfield development. The available reserves calculated by value of the movable oil saturation, which is tested by the new method, is the upper limit value of recoverable reserves by water flooding. Accurate test of the movable oil saturation provide theory evidence for available reserves demarcation and recoverable effect of reservoirs.