Visualization Study On Fluid Distribution In Core Based On Low-field MRI Method

The core visualization method of low-field magnetic resonance imaging(MRI)is a new developing technology, which has the features of rapidity, non-destructionand visualization. Its application in petroleum engineering is still in the exploratorystage. This new non-destructive testing technology can be used to visually displaythe fluid distribution during core flow test, which is important to reveal theoil-displacement mechanism of different agents. Based on the project conducted bythe author during his master-degree study, the low-field MRI core flow system hasbeen improved significantly. With optimization on the test parameters andelimination of the interference factors, the real-time images of fluid distributionduring displacement process are obtained successfully, and the oil saturation fields atdifferent time and position are then calculated. The characteristics of watermigration and formation process of preferential migration channel during theprocess of oil being displaced by water are studied in detail. The modes of existenceand their corresponding influence scope of end effect in core flow test are finallyinvestigated. Detailed work and achievements are:1) The technical features, development status and problems in application ofseveral visualization methods were analyzed and summarized. Compared to othermeans of visualization, MRI method is more suitable for the detection of fluiddistribution information in core. Base on the summarization of the relaxationmechanism, and visualization method of fluid and the basic principles of MRI inporous media，the adjustment and optimization of key testing parameters of MRIvisualization experiments were elaborated, including the imaging direction,thickness of slice and imaging position.2) An improved domestic low-field MRI core flow system was successfullymade. The improvement schemes include:1) increasing signal shielding through restructuring the circuit,2) optimizing displacement agent and surroundingpressure fluid in displacement experiment,3) optimizing imaging sequence.3) With the improved low-field MRI core flow system, oil saturation wasstudied in core. Through the quantitative analysis on MRI imaging signals in theprocess of oil being displaced by water, the oil saturations in core at different timeand position were obtained, which is consistent with the results of traditionalmethods. At the same time, the saturation at local location was also calculated.4) Based on MRI visualization methods, the characteristics of fluid migrationand distribution in core during the process of oil being displaced by water werestudied. Combining with both sagittal and cross section core biopsy methods, weobtained the distribution of oil or water at different times and different positions.The images clearly display the moving positions of oil-water interface at differenttimes. Experimental results show that the status of water moving in cores withdifferent physical properties is different. The water moves with uniform speed insome cases, while in other cases, it invades and forms preferrable channels which isgradually widened with the amount of displacement. It is also found that the residualoil mainly exists in the outer side of the channel.5) The feature images of fluid with end effects in water displacing oilexperiments were obtained with MRI. The modes of existence and theircorresponding influence scope of end effect in core flow test were furtherinvestigated.