Analysis Of Effectiveness Reservoir Of The Middle And Lower Of Third Member Of Shahejie Formation In The Baimiao And Its Surrounding Area, Dongpu Sag

Drilling data have been uncover that there are more frequent hydrocarbonappearances and bigger exploration potential in the deep Shahejie formation (S3-S4),Baimiao and its surrounding areas of Dongpu sag. However, for this issue, such as thereservoir space type, development characteristics, genetic mechanism and majorcontrolling factors, which will comprehensively control the effective reservoir of thedeep formation, are not clear and never conduct the systematic research, and then itwill seriously restrict exploration. Therefore, three aspects of problem will be solvedin this paper, they are:(1) summarizing the composition of porosity type andevolution rules base on the analysis to diagenetic evolution,(2) systematicallystudying the main controlling factor and action model of the effective reservoir, and (3)discussing the classification methods and evaluation standards for the deep reservoirs.The study of sedimentary microfacies is the base of reservoir study, and it alsothe dominant factors for the property difference of the sandbody. The deep Shahejieformations (S3-S4) mainly grow the subfacies in Baimiao and its surrounding area,such as the fan delta front and delta front, including the sedimentary microfacies asthe underwater distributary channel, estuary dam and sheet sand, of the sandstonesresulted from the underwater distributary channel is the most advantageous sandbody.For the reason of deposition, diagenesis and tectonic movement, which willcombine with each other to act the deep reservoirs, and result in the various porositytypes, and according to their generation mechanics, can be classified into the residualoriginal pore, mixed pore and secondary pore and fissures. Most of the pore inreservoir was evolved from the original pore. The Pore type within the different highabnormal pore zone possess the following distribution characteristics:(1) the residualoriginal pore which will contribute to the current pore, is related to the reservoir burialdepth and porosity and rock components, generally speaking for the residual originalpore, the deeper burial depth is, the less contribution to the pore;(2) the bigger valueof the original porosity and the more contribution will be.(3) The distribution for thestructural fissures is wider in deep reservoirs, while their distribution is not unevenand among them are the vertical fissure and the fissures with high angle. The diagenetic process, occurred in the deep bury in the study area, are those asfollowings: secondary overgrowth of quartz, metasomatism and cementation ofanhydrite and ferrocalcite and ankerite, squeezing action and pressure solution,dissolution and asphalt packing action. Based on rock texture feature, palaeogeotherm,maturity of organic matter and clay mineral transformation, diagenetic stage of deepreservoir can be divided into three stages including mesozone rock A stage and Bstage and late diagenesis stage.Factors that influence and control effectiveness of the deep reservoir mainlyinclude the reservoir sediment characteristics(such as sandstone type, grain size,sorting, composition and thickness of single sand beds), distribution of fissure,hydrocarbon charging, acid fluid corrosion, compaction strength, etc., of which willinterplay and interact and inter-restrict each other and also with complicatedrelationship. Through analyzing and summarizing and highly generalization, it showsthat the most important factors of influencing and controlling the development andevolution of deep reservoir space in the study area can be clarified as three aspects,such as sediment characteristics, bury and compaction, fluid protection anddisplacement(hydrocarbon and acid fluids). Therefore, viewpoint of ternarycontrolling reservoir is put forward aiming at deep sandstone reservoir in Baimiao andsurrounding areas. Based on it and combined with diagenetic process and lithologiccharacteristics and grain size and porosity and permeability data and previous researchachievements in this research area, the reservoir space evolution models areconstructed for Baimiao and surrounding areas of Dongpu sag.Based on this and previous research results, the standard of classification fordeep reservoir in Baimiao and surrounding areas was constructed in this paper andreservoir assessment for important wells and blocks were carried out as follows. Themost middle formation of S3member in Baimiao area belongs to reservoir type Ⅰ~Ⅱ. The most lower formation of S3member in Baimiao area belongs to reservoir typeⅢ and minority belongs to reservoir type Ⅱ. The middle formation of S3member inDuzhai area mainly belongs to tight reservoir typeⅠ or general reservoir Ⅱ. Thelower formation of S3member of burial depth above4250m generally belongs to thetight reservoir type Ⅱ. The middle(upper) formation of S3member in Qiaokou areamainly belongs to reservoir type Ⅰ and the middle(lower) formation of S3memberare equivalent to tight reservoir type Ⅰ~Ⅱ. The lower formation of S3member ofburial depth above4250m generally belong to the tight reservoir type Ⅲ.