A Novel Method to Construct Capillary Pressure Curves by Using NMR Log Data and Its Application in Reservoir Evaluation

Abstract

Abstract In view of the problem that there is a good agreement with big porosity while a bifurcation with small porosity in practical applications of the method that a linear function of the conversion scale is used to construct NMR capillary pressure curves, it is proved by profound analysis of the morphologic characteristics of mercury intrusion capillary pressure curves that capillary pressure curves can be constructed continuously only if the mercury saturation corresponding to different mercury pressures is calculated. Based on the theory of J function and the classical SDR model, by analyzing 50 core samples, the mercury injection experiment and NMR measurement of which are taken simultaneously, a NMR capillary pressure curve constructing method is put forward and a model of NMR capillary pressure curve construction is established. Accuracy of the new method is verified by analysis of morphologic characteristics of the mercury injection capillary pressure curves comparing with the real ones. Processing analysis of the well A01 of an oilfield is carried out with the method to evaluate the reservoir pore structure and calculate the original reservoir water saturation. The result shows that the method is effective and its deployment can be carried out in the oilfields. Introduction With the world's ever increasing demand for oil resources, and continuous improvement in exploration technology, the intensity of exploration for complicated reservoirs increases, especially for development of reservoirs with low porosity and low permeability1. For such complicated reservoirs, it's urgent for geologists to understand the characteristics of their pore structure in order to reduce exploration and development risks. At present, the most direct and effective way to evaluate reservoir pore structure is mercury injection experiment. Mercury-injection capillary pressure curves are obtained through mercury injection experimental analysis of cores to evaluate reservoir pore structure. However, restrained by experimental conditions, the use of core analysis to obtain mercury-injection capillary pressure data is very expensive and toxic mercury which is used as experiment medium does permanent damage to the cores. Therefore it is impossible to carry on continuous core analysis to the entire well, and only limited cores from main formations of interest are selected to carry on mercury injection experiment, which cannot result in continuous evaluation on pore structure of the entire reservoir intervals.