A Study On Formation And Sedimentary Characteristics Of The South Subsag In Aladabusi Sag WuNiTe Depression Of Erlian Basin

The south subsag of Aladabusi Sag at the northeast of Erlian Basin, the subject to a dustpan shape of east west super loop fault depression. The south subsag is the new area of oil and gas exploration in the Erlian basin exploration and development of Yanchang Oil Company. At the present, the study area has been completed 11 seismic survey line of two-dimension, and a parameter well. According to gravity, magnetic and electric exploration results, and the two-dimension seismic data of previous confirmed that the subsag is divided into south and north subsags. Subsags have complete structure, with the basic conditions of create, transport, gather in theory. Combined with the exploration and development informations of adjacent regions of Gaolihan subsag, Buridun subsag, such as theoretical predict that Aladabusi Sag has good exploration prospects. But from the drilling result of the parameter well-Yan’acan in 2013, the strata, lithology characteristics, oil and gas, hydrocarbon source rock and the characteristics of sedimentary facies are bigger difference with the current understanding of the sag of the mainstream, so it need to have research of the sedimentary strata and sedimentary facies characteristics, and wish to provide necessary geological theory basis for the next exploration in the study area.This paper through the interpretation of the seismic data and comparison among adjacent regions, and combined with analysis of the drilling of Yan’acan 1 well to study the characteristics of stratum and sedimentary facies. Research show that Aladabusi Sag formed in extensional tectonic background, and fault develop well of along the NE-SW distribution, The vertical performance superimposed single fault of half graben sag structure. The south subsag of Aladabusi Sag’s formation that from bottom to top as follows:K1ba group, K1bt group(K1bt1、K1bt2), Kibs group in Mesozoic and Cenozoic. The thick area of K1ba group is downdropped in concave fault. The lithological characteristics is argillaceous siltstone, silty mudstone and shale in the shore and shallow lake environment. Low gamma ray, high sound waves, high resistance, is the log characteristics. Sporopollen features are the Pilosisporites-Protoconiferus-Erlianpollis. K1bt1 group’s formation thickness up to 750m, the sedimentary center in the north area is enlarge, lithologic characteristics in environment of braided river delta front deposition of glutenite, log characteristics are the low gamma ray, low sound waves, small resistance, and Sporopollen assemblage is Megamonosporites-Pseudopicea-Pinuspollenites; K1bt2 group’s formation thickness up to 700m, the depocenter located in downdropped block of fault nearby, lithology are mainly conglomeratic sandstone and glutenite, log characteristics are gamma changes little, change of sound waves in the upper is big, and lower change is small, low resistance, The pollen is characterized by Protopicea-Protopinus-Palaeoconiferus, K1bs group formation lithology is mainly grey-mudstone, conglomeratic coarse sandstone and little black thin carbonaceous mudstone, also have 7 black coal seam; the characteristics of logging curves is gamma varies within a small range, sonic serrated change and in coal seam showed high interval transit time; sporopollen assemblage is Classopollis-pinae.The provenance of Aladabusi depression mainly from the Baiyinhushuo and Baqi projections around the basin, study area is divided into deltaic, lacustrine, underwater fan 3 large phases, and subdivided into four sub-phases and 11 micro-phase, which in each depositional period has development. K1ba period is rapid phase into a lake, basin progressively larger scope, development shallow lake subphase sediments, mainly characterized by the phenomenon of shallow lake sandbar, shallow lake mud-sand and shallow lake mud frequently interbedded; the sag into lake mainly deceloped in K1bt1 period, then the lake area expanded, the fault activity enhancement and obvious control effect on deposition; in K1bt2 period fault development continued, the lake area decreased, still there is an obvious control effect on depression; the tectonic activity was basicly end in K1bs period and the fault is nondevelopment. Sedimentary is mainly composed of fault type into a depression type deposit, a large sedimentary subsag in the sag of generally accepted deposits, topographic relief decreases, then the subsag and the surroundings overall uplift and denudation. In caenozoicus, under the effect of the Himalayan movement, the study area had lifted again, accepted by the flood plain and river clastic sediments. In Quaternary period, the study area entered the sedimentary period of aeolian sand and aeolian clay.