| The third area of Shanghe oilfield is located in the south of Shanghe Oilfield, a part of Linshang brush tectonic fault zone in central uplift belt of Huimin sag in Jiyang depression, Bohai bay basin. With the accumulation of drilling data and test data,many problems have been exposed in the development process,which reveal that the geological research is lagged behind the production requirement with low recovery efficiency,so it is urgent to further the geological knowledge and enhance the reservoir comprehensive study.The significant problem facing at present is that the sand body changes rapidly laterally,together with no study in sedimentary micro-facies and detailed reservoir,leading to ambiguous understanding of oil sand body distribution laterally and vertically. Under present injection-production pattern, water injection response is slow and feed flow is bad. By correlating slim layers of upper Es3,a clear understanding of spatial distribution of interlayers and sand bodies and external geometric configuration of which can be acquired. Sedimentary micro-facies controls the distribution of sand bodies and is the decisive factor of reservoir physical properties. Only by identifying the depositional environment of each interlayer can realize the distribution of sand bodies laterally and vertically,and with a combination of governing factors of reservoir physical properties, characteristics and heterogeneity to forecast the favorable distribution area.Based on the isochronism, sedimentary facies-control and sedimentary cycle to principles determine correlation markers, upper submember of ES3is divided into6sand groups,and26layers.Besides,according to equal-elevation,superimposed sand bodies correlating, and facies change correlating patterns and so on,the stratigraphic correlation of upper submember of ES3is completed and formation frame model is established.With the analysis of testing data, based on the drill core observation and description, the petrological (component,composition,structure,distribution of sizes) study was developed. Most of the colours of mud-stone in the study area are gray,dark gray and somber black, and little of them are brown. This shows the depositional environment was reducing environment. Pyrite,siderite,other authigenic minerals and palaeontologic markers show the deep water depositional environment. The rock type is simple and mainly siltstone,fine sandstone and mudstone(shale). Directional structure is abundant, including erosion surface,gloove cast,load pocket,flame structure and slumping liquefied sediment flows,slumping convolute bedding,slumping mud pebble in tearing shape and small-sized contemporaneous fault structure,grading bedding. All of them are important symbols that identify turbidite deposit. At the same time, parallel bedding,massive bedding and climbing wavy bedding developing in siltstone and horizontal bedding developing in mudstone make up of the combination of ab,ae,bcde,cde and de segments in bouma sequence. This shows that the turbidite deposit types are from proximal deposit to distal deposit. One manifestation of thin bed turbidites is grittiness band and argillaceous band, which is very common in the study area. The lower fine-silty sandstone and upper silty mudstone or mudstone comprise several cyclothems, which were presented as the thin interbed of sandstone and mudstone. The bottom of fine-silty sandstone slightly fluctuate and lithologic character change suddenly. Miniature load casts appear frequently. It has mormally graded structure and horizontal bedding develop in the upper part. Ripple lamination can be found in few drill cores. The constitution is equivalent to ade or de segment in bouma sequence. Using grain size analysis data of54samples in well Shang13-107, grain size probability curve can be made. Through the analysis of them, curve types in the study area can be divided into arcuation,two-section,triple section and several section. The common features of these curves are high content of suspension and bad sorting. Point groups in C-M are basically parallel to C=M base line. This shows the gravity current deposit fast and are nonsorted. Sand body in borehole log are high amplitude boxform,campaniform,infundibuliform and dactylineform. Through the observation of drill core,comprehensive logging data,well logging data,chemical testing data,regional geological data and typical sedimentary structure,distribution of sand body thickness, upper submember of ES3in the third area of Shanghe Oilfield developed turbidite fan and lake including middle fan, outer fan and semi-deep to deep lake,which can be divided to channel,interchannel, channel lateral margin,outer fan mud, creeping turbidite sandbodies and semi-deep lake to deep lake mud microfacies.Through the analysis of single well facies, well-connection profile facies and plane facies, each sand group experienced a process of water regression and fan’s propulsion. Sand body in braided channel are well developped. The distribution of semi-deep lake to deep lake are in the middle of braided channel. Changing trend of sand body in a period are not exactly the same. This shows that different direction of provenance may coexist or the development direction of sand body in different period may change to a certain extent. From previous studies, the upper submember of ES3in the third area of Shanghe Oilfield is apart of Jishan sandbody. It is located in the front of Jishan delta. The advancing of the delta make the deposits accumulated continuously, and the thickness increase gradually. This impels the slope gradient of the front increasing. Because of the trigger of gravity,earthquake,fault and flood, these deposits in front of the sand body will cause turbidity transport and make them deposit in front continually, forming the slump turbidite fan series. To some extent, this depositional model explains the development characteristics of slumping turbidite fan in this area.The reservoir type of upper submember of ES3in this area is mainly feldspar detritus quartz sandstone and less detritus feldspar sandstone. The reservoir space is dominated by secondary pore,including intergranular dissolution pores, intragranular dissolution pores, moldic pores and micro-pores and intergranular dissolution pores do the most contribution to the reservoir’s capability. Analysis assay data and secondary logging interpretation manifest that upper submember of ES3is middle pore and low permeability,super-low permeability reservoir. Reservoir physical properties are dominantly controlled by the distribution of sedimentary facies via combinating planar graphs of sedimentary facies,porosity and permeability. Braided channel microfacies can be profitable reservoir because of large depositional thickness and large grain size. |
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