Study On Reservoir Heterogeneity Based On Nano-scale

This paper took three blocks of Shengli Oilfield ( Ninghai, Shengtuo, Guangli ) in Dongying Sag for example, selecting each of the main oil-bearing series (sandstone) as the research object, based on the analysis in the polarizing microscope, using three kinds of precision instruments, which are field emission scanning electron microscopy, high resolution transmission electron microscopy and atomic force microscopy, to make nano-scale observation and analysis of the rock matrix minerals, clay minerals and pore-throat structure. Summed up the nanometer scale morphology and structure characteristics of the mineral crystals, and thus reveal the nano-scale reservoir heterogeneity, and with the combination of oil and gas exploration and development results, pointed out the relationship between the nano-scale heterogeneity of the reservoir and hydrocarbon accumulation and distribution.The following research results and cognition were acquired mainly.(1) The nano-scale morphology and structure of the rock framework minerals, such as quartz and feldspar, were observed and analyzed. Found that there are pits similar as erosion, parallel ridges, crystal dislocations, grain kernal inclusions, young single crystals and many other nano-scale crystal structures developed in quartz. In feldspar, there developed parallel dents on the crystal planes, dissolution needle, infiltration pits, nano-scale thin layer of broken bands, crystal dislocations, micro-inclusions, kaolinization and other nano-scale structure characteris -tics. Reservoirs in different layers and different blocks have different framework mineral nano-scale heterogeneity.(2) The nano-scale morphology and structure characteristics of clay minerals were observed and described. The clay minerals are mainly kaolinite and illite-smectite mixed layer, there are also a small amount of halloysite, illite, and chlorite aggregates, the thickness of various types of clay minerals is less than 100nm, the gap between layers also belong to the nanometer scale. Nano-scale heterogeneity of clay minerals in different types of reservoirs have different combinations. (3) The nano-scale pore structure and pore-throat configuration relationships of the rocks were classified and summarized. The nano-scale primary pores include bedding joints, mineral cleavage seams, intracrystal pores, intergranular pores, intercrystalline joints and so on. The nano-scale secondary pores can be divided into three kinds, they are intragranular dissolved pores, dissolution joints and construction joints. And divided five types of nano-scale pore-throat configuration relationships, they are pore-throat consistant type, curved hourglass type, "X"-shaped pore cross type, "Feng "-shaped pore cross type and goblet-shaped cross joint type. Nano-scale heterogeneity of pore network has a good correspondence with micro-scale heterogeneity of pore network.(4) The relationship between the nano-scale reservoir heterogeneity and the hydrocarbon accumulation and exploration was clarified. In general, the more developed cleavage joints and dissolution needles in feldspar, the more abundant the intergranular pore and joints in clay minerals, the more the pore-throat configuration biased in favor of the pore-throat consistant type, and thus better for hydrocarbon accumulation and development, otherwise negative.