The Study Of Relation Between Micro Sealing Characteristic Of Naturl Gas Cap Rocks And Distribution Of Naturl Gas In Nanpu Sag

Gas reservoir has been found in a plurality of layers in Nanpu Sag. Whether natural gas can be large-scale accumulated and good preservated, caprock conditions are important. This paper mainly uses geophysical, drilling, logging, logging and testing data, to identify and evaluate the micro sealing ability of caprock in Nanpu sag. First of all, in the plane distribution of cover determine the scope of the case, analysis of cover thickness plane distribution; Secondly, to create a single well mud ratio and 3D seismic attribute relationship, to determine the mud ratio plane distribution of caprock by using seismic attributes, and at the same time using coring displacement pressure test data to establish the relation between the cover layer depth and mud ratio, to determine the caprock displacement pressure distribution. Again, On the basis of single well overpressure values determined, establish pressure coefficient and the relationship between transverse wave and longitudinal wave, using the seismic method predict overpressure plane distribution; Finally to analysis the relationship between the cover thickness, mud ratio,displacement pressure and overpressure and distribution of oil and gas. Conclusions are drawn as follows:(1) there are a volcano rock(N1+2g) cover and five sets of(E3s2+3, E3s1, E3d3 s, E3d2 and N2 m regional caprocks in Nanpu sag;(2)the cover layer of mud than development is not balanced, the mud ratio of Ed2 is the biggest, No. 2 and No. 4 structural plane distribution is the best;(3) cover displacement pressure increases gradually vertically from the bottom to the top, on the plane of No. 2, No. 3 and No. 4 tectonic caprock displacement pressure is relatively large, on the whole the beach area is slightly higher than that of the land;(4) the caprock thickness, mud ratio and displacement pressure have a positive correlation with the distribution of gas, the lower limit of the thickness of mudstone caprock and volcano caprock of sealing gas is 125 m and 82 m, the mud ratio limit is 0.66 and 0.185, the displacement pressure limit is 2.2MPa and 3.3MPa;(5) Cap rock overpressure development and development degree of natural gas with coupling, overpressure development areas, natural gas reservoirs and deep, pressure seal, and relatively small areas, overpressure gas accumulation horizon shallow, pressure seal was not significant.