Research On The Logging Evaluation Methods Of Low Permeability Sandstone Gas Reservoir In The Eastern Ordos Basin

It’s the typical lithologic gas pool that low permeability sandstone gas reservoir in the eastern Ordos Basin. Compared with other formations, the pore space is very small and the permeability is very poor. Affected by the source and sedimentary environment, it has the characteristics of complicated mineral constituent, complex pore structure, diverse pore types and little difference among the different fliuds on the logging responses in reservoir. Take account of these problems, this paper mainly carried out studying on reservoir well-logging evaluation punctiliously targeted with the formation of Permian,upper palaeozoic, using multiply information of core, geology, logging, gas testing etc.Based on the actual situation of study area, the logging data have been systematically processed by the standardization of trend surface method, firstly; Then the basic properties of lithology, physical property, gas-bearing, electrical characteristics pore structure features and their relationships are systematically analyzed. Combined with X-ray diffraction whole rock analysis and the natural gamma log response, the clay content in this area is determined, through the models of core calibration and the flow zone indicators, the porosity and permeanility are acquired in different layers. Meanwhile the Coates and SDR modles are established because of the NMR experiment. Use of rock electrical property exerperment, contrasting the Archie’s formula and the water saturation modle of acoustic- neuron cross plot. In addition, irreducible water saturation interpretation modle was builded by the NMR experiment irreducible water and the reservoir quality index. At last, From the response mechanism of low permeability sandstone gas reservoir, it is detailedly researched that non-electric means of gas identification such as the method of conventional logging, dipole shear wave logging, overlapping process of NMR porosity and density porosity etc,as well as a way of gas content evalution utilizing Xu-White modle is tried to do a tentative exploration and obtain a good application effect.Some results of the studies show that the relative weak hydrodynamic force and near provenance deposits make the reservoir well sorted and general rounded; the important effect of the effective pore space is dissolution, and a high content of clay and sundry, rock debris is the reason for the poor physical properties. The Archie’s formula and the water saturation modle of acoustic-neuron cross plot have a high consistency with hermetic core, and the latter eliminates the influence on acoustic and neutron log response of natural gas at a certain degree, it is independent of the resistivity logging, avoids the problem of calculating the formation water resistivity. The non-electric means of fluid factor and Xu-White modle based on dipole shear wave logging, indicate the hydrocarbon reservoir more intuitively and more clearly in the perspective of qualitative and semi-quantitative, which achieves good results and guarantees the identification accuracy.