The Study On The Distribution Rules Of Remaining Oil In Heavy Oil Reservoirs At Chenjiazhuang Oilfield

The factors that influence remaining oil distribution are complex and various,the producing extent are different and distribution rules are special in heavy oil reservoirs.Therefore,a large-scale heavy oil region,i.e.Chenjiazhuang Oilfield is taken as the study case.Due to the difference of reservoirs and heavy oil characteristics,different development mehtods are implemented in different regions,such as water flooding,steam stimulation and steam flooding.Appearently,it is relatively a better case to study remaining oil in heavy oil reservoirs.The heavy oil reservoirs are classified into 2 categories.One is the ordinary heavy oil reservoirs with favorable properties,which is mainly drived by water flooding.Another is extra and super heavy oil reservoirs in the south region,which is mainly developed with thermal recovery method.These research are not only helpful to the exploration of heavy remaining oil,but also meaningful to some basic theories,science research and development plans.There are too many factors that control the distribution of remaining oil in heavy oil reservoirs.Therefore,relative research cannot be only limited to reservoir architectures,but needs full consideration of heavy oil properties,reservoir properties and development methods.Numerical models of remaining oil are also needed to finish quantitative research.Therefore,the research methods of remaining heavy oil and conventional oil are different.On the basis of general analysis,some special experiment of heavy oil are carry out.Through geological modeling and numerical simulation,remaining oil models are established.Therefore,quantitative analysis of remaining oil distribution is realized.In addition to above methods,some research and innovative results are shown as follows:Through the analysis of reservoir lothologies and well log characteristics,a new method to quantitatively identify lithologies in the remaining oil layer is invented.Tradtional methods are are all qualitative methods,such as core observation,microscopic identification,and web methods,and there is still no quantitative methods at present.Therefore,a quantitative lithology identification method is found.Firstly,the lithologies of cores and cast slices are used to accurately define some lithologies.Then,based on crossplot charts,the critical values between major lithologies are determined.With array induction curves,mudstone,mud sandstone conglomerate and glutenite are distinguished.The density curves can further distinguish sandstone,conglomerate,mud siltstone and argillaceous conglomerate.The porosity logs and wave impedance curves can distinguish sandstone and conglomerate.Finally,there are altogether 7 lithologies identified.Judging from the results,the correct rate is more than 75% in general.In the research of reservoir properties and heterogeneities,apart from conventional experiments,thermal properties,high temp seepage characteristics,and NMR experiments are carried out.The changes of properties and fluid are tested.The comparisons and evaluations of heavy oil reservoir characteristics are also finished with these special experiments.Reservoir characteristics,development conditions,and remaining oil are comprehensively studied.Some analysis and evaluation on oil layers are realized.Heavy oil properties have great influence on the distribution of remaining oil.Therefore,some geochemical index sensitive to water-drive are selected to obtain geochemical properties changes during development process,and the thickening mechanism of crude oil is revealed.Two new models are constructed,including reservoir formation model of extremely shallow oil sand and formation model caused by water flooding.Furthermore,it reveals that high-water stage in Shengli Oilfield is actually caused by oil densification,with not high water content in cores.It is also concluded that long-term water flooding is the most important factor that makes oil viscous and hard to be exploited.Based on previous research of reservoir and heavy oil characteristics,the distribution rules of remaining oil in different heavy oil reservoirs are summarized as follows:(1)As for ordinary heavy oil reservoirs,remaining oil is more enriched in the areas with high reservoir heterogeneity,such as the edges of river channels.It is also concentrated in the layers separated by mudstone in the plane.Vertically,the distribution of remaining heavy oil is less influenced by structure,but by water/steam injection.Oil is also enriched in the layers with strong vertical heterogeneity.In 3D space,the secondary flow line is the position where oil is enriched.Thin layers and low flow velocity regions result in high concentration of remaining oil.(2)As for extra heavy oil reservoirs,vertically the remaining oil in the layer is influenced by the heterogeneity of reservoir,interlayers and perforation layers.In general,due to steam overlap,the remaining oil in the lower layer is more enriched,and it is completely contrary to the thin oil reservoirs.Partial high oil saturation appears in unopened oil layers.The oil enrichment zones can be formed at the upper part of the interlayers.Remaining oil usually concentrates in low permeability and disconnected layers.In the plane,the remaining oil distribution is controlled by sedimentary microfacies and reservoir heterogeneity,such as the sides of river channels and high heterogeneity regions.(3)As for heavy oil reservoirs of strong edge-bottom water,oil-water interfaces of most heavy oil reservoirs is not horizontal,but has a certain inclination.The remaining oil is more concentrated in the secondary main line.The area of oil-water transition zone is larger.When steam injection wells in oil-water transition zone is closed,the remaining oil saturation of heavy oil reservoirs will be more or less affected by side water invasion.(4)As for remaining oil of asphalt sand in extremely shallow heavy oil reservoir,remaining oil detection results of cored wells reveal that the oil saturation is still very high after many years of steam injection.Oil saturations of many core samples is close to the original,which show great potential for development.