Study On Reservoir Petrophysical Parameters Test Method And Its Application In Ultra-low Permeability Petroleum Reservoir

Reservoir physical simulation is the main method to provide reservoir petrophysical parameters to oilfield development and study fluid flow mechanism in petroleum reservoir rocks. Additionally, some new flow mechanism or enhanced oil recovery methods may be discovered in physical simulations. Afterwards, the new mathematical models can be established describing the new flow phenomenon which can improve the prediction accuracy of reservoir engineering and numerical simulation.However, the conventional reservoir parameters test methods and petroleum industry standards are generally developed to the high permeability petroleum reservoirs. There are many restrictions included in the existing industry standards. The wrong petrophysical parameters and rock core experimental results may be obtained if the conventional physical simulation methods were used in the development of ultra-low permeability reservoirs. Therefore, the wrong experimental results can not correctly guide the effective development of ultra-low permeability reservoirs. Based on a great number of literature review, the new pulse-decay permeability test method and wettability measurement using nuclear magnetic resonance technique were systematically studied in this research in order to complement petrophysical parameters test method series. Permeability stress-sensitivity of ultra-low permeability reservoir and relative permeability test and calculation methods were also studied in this paper.Firstly, the unsteady-state pulse-decay permeability test method was systematically studied including operational methods, accuracy of the test results and different sources of experimental error. Experimental results demonstrate that the pulse-decay permeability of tight rock is always less than the Klinkenberg-corrected permeability in the case of the same net confining pressure. The lower the rock gas permeability, the greater the difference between pulse-decay permeability and Klinkenberg-corrected permeability. The difference of the operational methods and the combination of effective stress between pulse-decay permeability and Klinkenberg-corrected permeability is one of the main reasons causing the pulse-decay permeability is less than the Klinkenberg-corrected permeability. Finally, experimental test specification of pulse-decay permeability was established in this dissertation.A novel experimental method was proposed to test reservoir rock wettability using Nuclear Magnetic Resonance (NMR) technique. Moreover, the complete experimental operation process and calculation method were also build. Experimental results indicate that there is a good linear relationship between the conventional wettability index (Amott index, AI) and the NMR signal ratio which is the ratio of NMR signal less than the T2cutoff to the total NMR signal in the case of rock saturated oil state. Therefore, reservoir rock wettability can be obtained from its NMR T2 spectrum at saturated oil state. The new method significantly improves test efficiency of ultra-low permeability reservoir rock and there is no need to change reservoir rock original fluid saturation distribution.Permeability stress-sensitivity of ultra-low permeability reservoir rock was comparatively studied using different types of fluid media. The comparative results suggest that there is significant difference between different types of fluid media permeability stress-sensitivity. Oil effective permeability stress-sensitivity at irreducible water saturation is always stronger than that of gas and water permeability. Consequently, oil should be used as the fluid media in the permeability stress-sensitivity evaluation. Meanwhile, wettability of the oil reservoir should also be considered in the experiment. Effect of the way of the combination of effective stress on the permeability stress-sensitivity was also researched. It was found that the conventional constant-pore pressure but variable-confining pressure method underestimates the low permeability volcanic gas reservoir permeability stress-sensitivity. Rock core and reservoir permeability stress-sensitivity evaluation experiments were clearly distinguished in this paper. It was found that the oil reservoir permeability stress-sensitivity is weak but the gas reservoir permeability stress-sensitivity is strong.Based on the previous research results, the new analytical formulas including capillary pressure were derived in which the oil effective permeability at irreducible water saturation was considered as the benchmark permeability. Experimental and numerical simulation research all shows that the classic relative permeability calculation formulas (JBN formulas) can not give the correct relative permeability of ultra-low permeability reservoir. Some test and calculation limitations were analyzed during the measurement of water and oil relative permeability of ultra-low permeability reservoir and several methods which can solving the above problems were pointed out in the last chapter.