| Micro-heterogeneity of tight reservoirs is the key to evaluate the“sweet spots”of tight oil.To characterizate the micro-heterogeneity of tight reservoir from Paleogene Hetaoyuan Formation in the Biyang,X-ray diffraction,pore permeability analysis,high pressure mercury injection,scanning electron microscopy,focused ion beam scanning electron microscopy and micro-CT were applied and quantitative evaluation criteria of heterogeneity was established was established via CV equal to 0.1.Using this criterion,high-quality reservoir was selected by combining the evaluation criteria,physical property cutoffs and upper limitThe results show that the tight sandstone are mainly lithic feldspathic sandstone and feldspathic lithic sandstone.The average contents feldspar,quartz,calcite、dolomite and Clay are 27.7%,53.1%,3.6%,2.4%and 8.0%respectively.The types of reservoir space are mainly intergranular pores and intergranular pores.Clay minerals are the mainly components minerals and make up 23.7%in shale,the percentages of carbonate,quartz and feldspar contents are20.0%,20.6 and 23.0%respectively.The mainly types of shale reservoir are clay minerals intergranular pores and carbonate dissolution pore.Absolutely,there are also some organic pores and micro-cracks in the shale reservoir.Physical characteristics and microscopic pore-throat heterogeneity were qualitativly and quantitativly characterizated from the multi-angle and multi-scale by scanning electron microscopy,high pressure mercury injection,focused ion beam scanning electron microscopy,micro CT and other methods.The result shows that the peaks of pore size distribution in mudstone and tight sandstone are 100-500nm and>10μm respectively,but the main distribution of pore number are all less than 50nm.According to the characterization of the mercury injection curve of the tight sandstone reservoirs,the tight sandstone reservoirs are divided into four classification and the evaluation standard for reservoir classification was established.The type I reservoir developed macropores,and the main pore throat radius are distributed 1μm to10μm.Its porosity is 13.1%,and permeability is 91.72×10-3um2.Type II reservoir developed macropores and mesopores.The main pore throat radius distributions range from 0.3μm to 1μm,the porosity was distributed in 4.8-8.8%,and the permeability was distributed in 0.332×10-3um2-1.378×10-3um2.Mesopores and Microporous are dominated in Type III reservoirs.and the pore throat radius of the main reservoir ranges from 0.05 to 0.30μm,the porosity is 1.2-5.5%,and the permeability is0.013×10-3um2-0.273×10-3um2.The type IV reservoir developed Microporous,accounting for more than 70%.The main pore throat radius distribution is less than 0.05μm,the porosity is distributed in 0.3%-4.7%,and the permeability is distributed in 0.006×10-3um2-2.981×10-3um2.Pore morphology diagram and evaluation criteria of Pore morphology are also established through morphological differences of different pores in scanning electron microscope.Through the pore morphology diagram and evaluation criteria,the pore morphologies in different minerals were evaluated.The results showed that organic pores>intergranular pores>clay minerals pores.At the same time,a quantitative evaluation criteria of heterogeneity was established.The heterogeneous level is divided by the variation coefficient（CV=0.1）and the physical property cutoffs was study.With the increase of depth,the physical property cutoffs of reservoir gradually reduced.From 2100m to 3450m,the physical property cutoffs of reservoir porosity calculated from different methods was decreased from 7.00%to 2.02%;the physical property cutoffs of permeability was 0.048×10-3μm2 to 0.017×10-3μm2 from 3000m to 3450m;The upper limit of porosity is 9.98%,and the upper limit of permeability is 3.75×10-3μm2.Using the physical property cutoffs,theφ/CV and the upper limit,the high-quality tight reservoir was selected the V oil group of Hetaoyuan formation. |
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