Research On Identification Of Oil And Water Member In The Triassic Of Yanchang Formation In Yanhewan Block Of Xingzichuan Oilfield

The reservoir of Yanchang formation is one of the main pay zones in Yanhewan block of Xingzichuan oil field whose kind is tight sandstone of low porosity and low permeability.It includes various pore types and its pore structure is very complex.Lithologic reservoirs controlled by channel are the main type in the study area.Depositional environment results in the differences between granularities of detritus and the complexity in the logging evaluation,as well as the difficulty in the identification of the oil and water member.The former studies in this area focused on fractures,source directions and petrophysical facies.By the main means of assaying,microscopic observations and mathematical statistics,this paper studies the stratigraphic division and correlation during Yanchang formation,adding up the petrologic features,pore structures and the physical property characteristics,and the four-property relationships and the methods of identifying the water and oil layers by qualitative and quantitative ways are taken into consideration,thus the following conclusions could be drawn:The direction of tectonic activity in the study area is mainly in vertical,the characteristic of Yanchang formation shows high in east and low in west with west-dip monocline but there are local high structures in yan6,zhentan5 and hao902 area which shows nose-shaped uplift.The types of the pore are mainly composed of the secondary dissolved pores.The characters of secondary dissolved pores are different between Chang2 and Chang6 members as the types of interstitial material in Chang2 and Chang6 member differ a lot.The types of Chang2 pore are mainly calcite dissolution holes while dissolved pores of laumontite are in Chang6 formation.The porosity of Chang2 formation ranges from 10%to 18%,and the permeability from 0.1×10-3?m2 to 50×10-3?m;however,the porosity of Chang6 formation varies from 8%to 12%,and the permeability from 0.02×10-3?m2 to 10×10-3?m.The study on four-property relationships shows that physical property is affected obviously by lithology and the physical property of medium sandstone is better than fine sandstone.Although the feature of siltstone is better individually but the most sample do not have reserves capacity.The relationship of lithology and electrical characteristic shows that the resistivity decreases with the particle size decreasing.Comprehensively analyzing the relationship of lithology,electrical feature and physical property the factors above make sense on the oil saturation.The method of curve overlapping with the characters of well logging can identify the water and oil members qualitatively.The steps are as follows:firstly,we divide the permeable layers with GR and SP curves,referring to the result of four-property relationship for the GR lower limit,and then overlap the AC and ILD curves to permeable layers.According to the overlapping area and its shape,the oil member,water member and dry member can be identified respectively.Cross plots use the data of multiple wells and the results can be more universal,because it reduces the mistakes generated by the differences between wells,the oil and water member could be identified in the map by combining the testing and production information,providing evidence for identification quantitively.Reservoir model offer reference to interpretation quantitatively of oil-bearing saturation.And then the lower limit of porosity,resistivity and saturation can be set by the Archie formula,taking the lower limit of correlation diagram and the four-property relationship into account.