A Research Of Reservoir Characteristics Of Shasanzhong2～4Groups Of Wennan Oilfield

Wenliu area is located in Puyang city, Henan Province. The structural position is in the central of Dongpu sag. Pucheng oilfield is in the northern. Wenliu area and Qiaokou oilfield are separated by yellow river in the southern. In the east, there is Qianliyuan sag, and Liutong-haitongji source sag is in the west. Wenliu area includes Wenbei(wendong&wenzhong) oilfield and Wennan oilfield. Overall, Wennan oilfield appears the garden structure, of which boths sides are higher than the middle and west is higher than the east. Eastern stratum structure is simple, while the west is more complex. The Cenozoic strata are mainly composed of a set of clastic sedimentary mudstone with sand and mudstone interbedding, the mudstone layer sandwiches multiple sets of thick salt rock, mud and other gypsum-salt and oil shale. Shasanzhong section of shahejie formation is one of the main oil-bearing series of wennan oilfield. The purpose of this study interval is Shahejie2-4sand group. The research area of sand blocks S3M2group area is approximately120Km2, S3M3～4sand group area is about80Km2, a total of275wells. Wennan oilfield is characterized in complex structure, deep buried reservoir, developmental instability, poor physical properties, strong heterogeneity, many oiled layers. Study on the characteristics and distribution of the reservoir is a key factor restricting the development. In the full absorption of previous research, this study takes theoretical sedimentology, geophysics, seismology, petroleum geology as a guide, a comprehensive application of drilling, well logging, seismic data to deeply study the sedimentary, reservoir, diagenesis and pore characteristics of the dense sandstone of shahejie group, shasanzhong2-4sand group.To take high resolution sequence stratigraphy as the theoretical basis, employ the method of "contrast sedimentary cycles, control hierarchically, combine wells and seismic, close skeleton", and through a variety of contrast modes, fully consider the contact between the sand to divide and contrast the layers of275wells of deposition of shasanzhong subsegment. Dividing2-4group into10small sand layers to establish stratigraphic framework of10isochronous stratigraphic unitsCombined with of seismic attributes and laboratory analysis, use geological data analysis cogitation and tools to reach the conclusion that the source directions of wennan area are southeast (major) and northwest (minor).After a series of core observation description, analysis the various phases logo, making full use of coring well datas to obtain the result that the sedimentary types of shasanzhong2～4sand group are delta phase (include delta front and delta), lake phase (shallow lake, semi-deep-deep lake) and gravity flow deposits. There are10kinds of micro-phase types:underwater distributary channel, far Shaba, sheet sand, mouth bar, inter-bay, beach sand, beach bar, turbidite, shallow lake mud and semi-deep～deep mud. And on this basis, the paper summarizes the unique delta sediment deposition and lake sediment deposition patterns of wennan area.The lithology of shasanzhong2～4group reservoir is mainly lithic feldspathic sandstone and feldspathic sandstone, with moderate to good sorting and roundness (times round the edge～times), medium compositional maturity. Cements are mainly carbonate cementation, followed by clay cementation. The reservoir has poor properties and showing an overall low-specifically low porosity, ultra-low permeability characteristics. According to flakes and electron microscopy methods, we find that the pore types of wennan area are primary intergranular pores, intergranular dissolved pores, feldspar and lithic dissolved pores, intergranular holes, mold holes and a small amout of micro-pore these6types, of which, intergranular pore dominates. The main throat types include curved sheet or sheet throat and slight throat, and also with a small amout of pore narrow type throats. The radius distribution of the throat is0.2～0.6μm, which plays a decisive role on the good or bad of perm.The reservoir of shasanzhong subsegmental in wennan area is mainly early diagenesis stage A. After a series of diagenesis, compaction educes porosity of sandstone reservoirs, two-stage cementation of carbonate and shale cause porosity greatly reduced, while the degree of dissolution of feldspar and other minerals is weak, so that the secondary porosity formation is limited, the physical properties of the target layers are poor.Studies show that the types of diagenetic facies of2-4sand group reservoir in wennan area are dissolutive diagenetic facies and dense diagenetic facies, of which, the former includes2kinds:porphyritic dissolution and dissolution pores diagenetic facies.The latter includes dense carbonate cementation and dense compaction, which will damage the reservoir, causing serious loss of primary porosity. Study on the factors of diagenetic facies shows that high feldspar content conducts porphyritic dissolution and dissolution pores diagenetic facies; while higher of the content of cuttings, cement, caulking, etc. does the opposite impact.Intergranular pore (native pore+dissolute pore+cement residues) is the main pore type of shasanzhong2-4sand group in wennan area. Unstable particles (feldspar, debris) is often in weakly dissolved, the formation of secondary porosity and alteration to the reservoir are limited. In the early sedimentary stage, the reservoir rock properties is not bad, then intense diagenesis makes reservoir a low permeability. The evolution of the pore is mainly controlled by diagenesis. At the same time, sedimentary facies also affects the prpperties, but not the controlling factors of this area. Densification is mainly due to the fact that cements formed in early cementation occupy a lot of pore space, resulting the demise of a large number of intergranular pore, then after the dissolution, later cementation occurred after mechanical compaction period, so the cements formed in this period basically cannot effect compaction, resulting in a significant reduction in porosity.On the basis of the physical properties of reservoir, sandstone thickness of sedimentary microfacies and diagenetic facies analysis, reservoir evaluation criteria is established. It can be divided into four categories:class I reservoir mainly porphyritic develops in the underwater distributary channel facies and beach bar microfacies, class II mainly develops in facies like estuary dam, underwater distributary channel, beach bar microfacies and so on. Overall, class Hand Illdominate in the reservoir of the study area. To summarize the quality control mechanism of reservoir:reservoir developed in underwater distributary channel is qualified reservoir, which has good properties, and its diagenetic types are porphyritic dissolution and dissolution pores diagenetic facies. Class Ⅰ, Ⅱ type reservoir need more focus to tap the potential.