Configuration And Heterogeneous Characteristics Of Braided River Reservoirs

To illustrate the configuration features of braided river reservoirs?identify configuration?analysis geometrical properties and physical properties of configuration?select parameters to quantitative expression heterogeneous characteristics of braided river reservoirs,we have used sedimentary geology?high-resolution sequence stratigraphy?mineral and Petrology and reservoir architecture analysis theory and method,and studied tight sandstone with low porosity and low permeability systematically by means of outcrop investigation?GR simulated logging?experimental analysis.The following has been achieved:?1?We divided H8 into two long-term cycles?four medium-term cycles and twelve short-term cycles by establishing framework of high resolution sequence stratigraphy.The main type of short-term cycle is A type with the increase half-turn,and both A₁?A₂ type well developed;there is a small amount of asymmetric cycles called C type,which general developed at the top of medium-term cycles and long-term cycles.?2?Identify four configurations in high-resolution sequence stratigraphy,which are channels?CH??longitudinal bars?LB??transverse bars?TB?and overbank fines?OF?.By making a summary of sedimentary characteristics of the various configuration elements,we know that:the main lithofacies of channels is conglomerate with massive bedding and trough cross bedding;longitudinal bar?LB?is a product of strong hydrodynamic conditions,and mark by large-scale?low-angle tabular cross bedding;transverse bar?TB?has positive rhythm and fine conglomerate with large-scale?high-angle tabular cross bedding,and there may be medium sands with horizontal bedding on the top of layer;overbank fine?OF?is rare in the strata,and it has grey-green or purple-red silt mud with horizontal bedding.?3?By summarizing GR logging response characteristics of four configurations,we found out that because of the remaining mud,GR under is higher than upper part,and the remaining mud is the result by not completely washed out.However,the positive cycle in the section is reverse cycle in GR response,we should judge the polarity by combining core and logging.The GR logging curve of longitudinal bars is jagged,each period of the formation of serrated GR is step response,and in the interior is relatively consistent.The GR logging curve at the top of transverse bar is much higher than the lower one,and that shows the mud of the lower part is not cleaned completed,and it need to combine core with logging to get further analysis like channels.We can tell that the GR logging curve of overbank fine is obviously higher,and this phenomenon can be used as a basis for tracking.The superposition of sand body is cutting overlap type in vertical mainly,and there is a few overlap types.The thickness of sand is relatively large.The mud layers are not developing.Sand body connected another directly.There is a high degree of mosaic in the lateral,so that sand bodies can be regional distributed.?4?Select a test section at the bottom of the H8 in the study area.Sampling at 30cm wide and 10cm high intervals for physical property analysis:GR measurements with15cm wide and 10cm high.Combine the analysis of the profile distribution characteristics of each physical parameters and the relationship between permeability and porosity,and choose the lorentz curve characterize the heterogeneity of the reservoir that separately for each configuration unit for quantitative characterization of heterogeneity.The heterogeneity of Channel?CH?along the direction of the ancient water has obvious decreasing trend.It generally belong to a homogeneous reservoir.The heterogeneous curve of Longitudinal bar?LB?assumes the tooth,near the source is low that belongs to a relatively homogeneous reservoir;downstream has Sharply rising trend that belongs to highly Heterogeneous reservoirs.The heterogeneous curveof Transverse bar?TB?like the serration,fluctuating frequency of curve has rising trend and fluctuation range become to small,but the overall trend remains unchanged.It belongs to a relatively homogeneous reservoir.Lorentz curve of permeability and porosity have a low relevance,and the pore connectivity is poor.Lorentz curve of overbank fines?OF?assumes the serration,but the heterogeneity in the middle is bigger than on both sides,middle belongs to highly uniform type,the heterogeneity to the minimum on the left side,homogeneous sand can be seen.The resulting show the best configuration unit according to the reservoir followed by Longitudinal bar?LB??Longitudinal bar?LB??Channel?CH?,Overbank fine-grained sediments are the interlayer that play a role as a barrier.?5?We have observed thin sections which are from the sample section through microscopes,and found out that debris in channels?CH??longitudinal bars?LB??transverse bars?TB?is relatively high.The main components are quartz-detritus sandstone?detritus quartz sandstone and lithc sandstone,a few feldspar,and some instability mineral like mica.The contact way between particles is from the point to the line.The degree of roundness of grain is poor,so is the degree of separation.There is always compaction and pressolution,and sometimes metasomatism?quatz overgrowth and dissolution.The pore connectivity is poor.But in overbank fine sedimentation,the size classification of grains is much better,and quartz content is higher with lower detritus content.The main component are quartz-detritus sandstone and quartz sandstone,and some quatz was overgrowth with some clay.