Micro-heterogeneity Of Gluite Reservoir And Its Effect On Oiliness In Well Area Ma 18,Junggar Basin

In recent years,with the discovery of the glutenite oilfield in the Mahu sag of the Junggar Basin,the evaluation of glutenite reservoirs has attracted much more attention.The glutenite in this area has some characteristics,including low maturity,coarse grain size and strong heterogeneity,which makes the prediction of“dessert”of the reservoir more difficult and limits the efficient development of glutenite reservoirs.Therefore,it is necessary to go on comprehensive research on micro-heterogeneity and oillines.This paper takes the glutenite of Baikouquan Formation in the Ma 18 well area of Junggar Basin as the research object..A variety of techniques,like X-ray diffraction,casting thin slices,scanning electron microscopy,nuclear magnetic resonance,high pressure mercury,low temperature nitrogen adsorption,constant velocity mercury injection and core electricity experiment,were carried out to study microscopic heterogeneity,oiliness and mobility.What's more on this basis,the effects of micro-heterogeneity on oiliness and mobility were discussed.The results from microscopic heterogeneity show that:(a)The mineral composition of the glutenite of the Baikouquan Formation in the Ma 18 Well area is mainly composed of quartz and feldspar,followed by clay minerals and the least calcite.However,the content of feldspar and clay minerals in different samples in this area is quite different.(b)There are various types of reservoir space in this area,including intragranular dissolved pores,intergranular pores,intergranular dissolved pores and grain edge joints.Among them,the intragranular dissolved pores are the most developed.The development of other three types were quite equivalent.(c)According to the morphological characteristics of the nuclear magnetic T₂ peak,the study area samples are divided into two types,and the comparative study of pore throat structure are conducted:porosity of Class I reservoir is greater than 8.5%,and its permeability is greater than 1.23m D.Intergranular pores and honeycomb dissolved pores in this type reservoirs show the main position.The T₂ spectrum shows obvious bimodal characteristics.During the high pressure mercury experience,the peak distribution of the pore throat is in the range of 0.2?m to 2?m.The structure has no sorting,the fractal dimension is small,and the heterogeneity is weak.The porosity of the Class II reservoir is less than 8.5%,and the permeability is less than 1.23m D.It is mainly composed of small-scale dissolved pores and inter-crystalline pores of clay minerals.the T₂ spectrum shows a single peak characteristic.the peak distribution of the pore throat is in the range of 0.01?m to 0.1?m.The pore throat structure has a high heterogeneous,and the fractal dimension is higher.The evaluation results of oiliness and mobility indicate that the T₁b₁ and T₁b₂ sections are oil-bearing intervals,but the oil saturation and the movable oil saturation are different between different samples.the better the quality of the glutenite reservoir,the higher the oil saturation and the better the mobility.The oil saturation of Class I reservoirs is 46.63%?64.33%,the dynamic oil saturation is 38.51%?52.25%,the oil displacement efficiency is more than 55%,while the oil saturation of Class II reservoirs is 26.27%?49.68%,movable oil The saturation is 11.14%to 30.35%,and the oil displacement efficiency is less than 35%.The effects of micro-heterogeneity of glutenite on oiliness and mobility in the study area are analyzed.For mineral composition and the type of reservoir space,the higher the feldspar content,the more favorable the dissolution to form a large number of intergranular/intragranular dissolved pores,which is more positive to the improvement of oil content of glutenite reservoirs.;the lower the clay mineral content,the less likely it is to block the pores and throat,which means that the oil and gas seepage capacity is stronger.In terms of microscopic pore-throat structure,the higher the proportion of large pores in glutenite reservoir,the better the pore-throat connectivity.The simpler the pore-throat structure,and the weaker the heterogeneity,the more oil-saturated and movable ratio of reservoir high.