| Liuhua11-1Oilfield is a large reef limestone reservoirs,that uplift on Dongsha Tuberositas of the Eastern Pearl River Mouth Basin, it has complicated geological conditions in the oil-water transition zone and serious biodegradation.The uncertainty of depth partition of oil-water interface is caused by the degradation of oil and serious heterogeneity of reef reservoir. In order to verify the results of well log interpretation, the method of organic geochemistry is used to divide the oil-water interface of Liuhua Oilfield.Based on the geological background of reservoir and setted LH11-1-4well, LH11-1-1A well, LH11-1-3well, LH11-1-2well, LH11-1E-1well, LH11-1E-2well as the object of study,the organic extract group components,Rock-Eval and GC/MS of the reservoir core and cuttings samples is analysed by experiments and in the further, researched the style of oil and characteristics of reservoir about Liuhua11-1Oilfield. According on the level of biological degradation, the parameters that can divede the oil-water interface is chosen to compare to the date from loggingThe characteristics of marked saturated hydrocarbon were analyzed from six wells in Liuhua Oilfield,the result shows:C23is the main peak tricyclic terpane series, tricyclic terpanes abundance of C19are far less than the C23(tricyclic terpane of C19/C23ranged from0.2to0.8).C24four ring terpanes is not rich, three pentacyclic terpene has a low content of oleanane,numerical value of gammacerane/C30H is very low, generally less than0.08, it may represent that the Wenchang formation source buried in lake water is light. Steranes has a relatively rich C30,4-methyl one, the value of C30,4-methyl steranes/C29regular steranes is ranged between0.8-1.0,C27-C28-C29regular steranes is represented distribution of approximate "V"type.The crude oil formed by Wenchang formation haslow double juniper alkane, abundance of W configuration is very low, abundance of T configuration is less than C30hopane.Together with crude oil,the vertical change of crude oil density and bio degradation of crude,the type of crude oil and charasteristics of reserviors’ accumulation is invested in the further in Liuhua11-1Oilfield,the result shows:Liuhua11-1oil reservoir is mainly formed by the Huizhou sag of the Wenchang formation through fault, unconformable surface, structure ridge long distance migration and accumulation,the hydrocarbon source rocks of Enping formation has no contribution to Liuhua11-1Oilfield. Single source of oil has laid the foundation for the more credible geochemical methods for the definition of oil-water interface. Based on the classification standard of crude oil biodegradation-Peters and Moldowan (1993), the suitable division standard is established to study crude oil biodegradation of six wells.According to the damage degree of rock saturated hydrocarbon compounds of GC/MS experiment, the level of single well vertical biological were divided. The results rshows:inthe direction toward the oil-water interface,biodegradation intensity of crude oil generally rises, some of the components of crude oil have regular changes, the level of whole oil biodegradation is4to5, hopanes, steranes were not obvious effected, no detectable C25-norhopane.Based on the comprehensive analysis of reservoir property, content of oil, density parameters of rock pyrolysis, Pow value of polar compounds, the value of (S1+S2)/residual oil, parameters of gammacerane/oleanane,and biological degradation level of chemical constituents in extracts of gradient features,It is found that the changes happened at the are the same or similar parameters, it shows that the rock hydrocarbon’s content,composition and physical,chemical properties and the level of biodegradation makes the regular changes at the direction of oil-water interface,and represents the abnormal performance at the point of oil-water interface,those changes are reflects the changes of oil-containing and degree of saturation,so the depth of oil-water interface can be established at the point of abnormal performance.The depths of oil-water interface LH11-1-4well,LH11-1-1A well,LH11-1-3well, LH11-1-2well,LH11-1E-1well,LH11-1E-2well are determined as1274.7m (TVDSS-1248.8m),1274.4m(TVDSS-1248.2m),1274.2m(TVDSS-1248.0m),1250.0m(TVDSS-1223.8m),1275.0m(TVDSS-1252.0m),1254.5m(TVDSS-1231.5m).The data shows, the oil-water interface are basically the same in half of6wells, but the others of oil-water interface changes great, this reflects the strong heterogeneity of reef reservoir. Moreover, the depth of oil-water interface about new determined six wells is more than the logging interpretation in generally.The analysis is that fluid properties tested by geochemistry is layer of oil-water,and the logging shows the layer of water-oil,the difference between the two kinds is the systematic error.The factors of controlling the Liuhua11-1Oilfield oil-water interface is analysed that it control by anticline as a whole, and fluid heterogeneity and reservoir skeleton heterogeneity has a great effect on the oil-water interface. |
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