EFFECTS OF VARIOUS KINDS OF DIAGENESIS ON PORE TEXTURE OF RESERVOIR SANDSTONES
Zhu Guohua (Scientific Research Institute of Petroleum Exploration and Development of the Changqing Oil Fleld ) Qiu Yinan ( Scientific Research Institute of Petroleum Exploration and Development, Be ijing )
The main reservoir sandstones in the Maling oil field and its periphery in Shan Xi-Gansu-Ningxia Basin, Northwest China-Yan-IO sandstones of lower Jurassic (including Fuxian formation ) are referred to as confined valley fill deposits. The difference of mineral compositions of the sandstone bodies deposited in different paleochannel systems leads to the different processes ofd iagenesis and then res ults in the difference of pore textures and reservoir properties of sandstones thus formed. Mechanical compaction during the immature period of mesodiagenesis seriously damages the primary intergranular pores of sandstones with more flexiblecomponents,but only slightly hits the interg pores in the quartzose sandstones. Cementation subsequent to the compaction usually and more easily occurs in the quartzose sandstone but not in the sandstone with more flexible elastics.when these two kinds of sands tones have undergone the process of diagenesis of different charactersand reduced their porosity to the same level,the pore-throat and the permeability of quartzose sandstones would be much larger than those of other sandstones because the intergranular pores in the former are still better developed. Secondary enlargement of quartz would destroy the homogeneity of primary pores and pore-throats of sandstones. Secondary solution porosity of subsurface origin improves the reservoir properties of Yan-IO sandstones.The differential precipitation of authigenic minerals and asphalts in sandstone bodies create the trapping conditions updip to the east of the South Area 1 in the Maling Oil field as well as the low permeability zone bordering the oil pool between the Middle and North Areas of the Field. The effects of clay minerals of different origin and their diagenesis on reservoir property of sandstones and on oil and water saturation and electric response of the reservoir rocks are different.And the effect of illite is far greater than that of the authigenic kaolinite.