Research On The Sedimentary Characteristics Of The Glutenite In Lower Cretaceous Of The Eastern Sag,Saihantala Depression,Erlian Basin

Glutenite is an important reservoir in Erlian Basin,which plays an important role in the oil and gas exploration of Erlian Basin.It is very important to find a relatively high quality"sweet spot"reservoirs in glutenite reservoirs.In recent years,glutenite reservoirs have been found in several depressions of Erlian Basin,especially in Saidong sag of Saihantala depression.A number of industrial oil flow wells have been drilled in the glutenite reservoir,showing a good exploration prospect.Therefore,this article makes an in-depth study of the Lower Cretaceous glutenite in the Saidong depression.In this paper,based on the previous studies,combined with fine observation description of core,and fine observation description slice under microscope.Based on the theory of sequence stratigraphy,sedimentology and reservoir geology,a comprehensive study of the stratigraphic framework,sedimentary characteristics,and oil-controlling characteristics of the Saidong Sag in Saihantala Depression to promote the large-scale discovery of oil and gas.According to the wave group response characteristics of seismic data,the logging curve shape change of logging data and core data,it is identified that there are two first-class marker beds?top of Tenger Formation and top of Alshan Formation?,one second-class marker bed(top of Tenger 2^ndsection)and four third-class marker beds from the Alshan Formation to Tenger Formation of Lower Cretaceousin of Saidong sag.The Tenger Formation can be divided into two sections Tenger 2^ndsection is divided into 5 sand groups,in which V sand group is the main oil-bearing section.Combined with core observation and description,well logging facies and seismic facies analysis,the lower Cretaceous of saidong trough mainly develops fan delta plain,with variegated and gray glutenite and purplish red mudstone,and surface of scour,graded and massive bedding;The lithology of the fan delta front is mainly a large set of light gray glutenite,and the natural potential curve is usually toothed box shaped,with scour surface,parallel and massive bedding;The lithology of braided river delta front is mainly variegated massive glutenite and glutenite,and the curve is generally box shaped and bell shaped,with cross bedding and parallel bedding;The lithology of nearshore subaqueous fan is mainly pebbly sandstone and glutenite,which are poor sorting.The curve is box shaped,tooth shaped and funnel-shaped,with progressive,massive and parallel bedding.Based on the identification marks of core facies,logging facies and seismic facies,combined with the analysis of single well facies and profile facies,the sedimentary plane distribution of the lower Cretaceous in the study area is analyzed:The period of the Alshan Formation was the early stage of sag development,and the depression gradually spread to form a lake basin,mainly developed fan delta facies,with a small range of lake facies.The tenger 1^stsection is the peak period of faulted lake basin development,with wide lake,deep water and long duration.During the whole period,the deep lake-semi-deep lake facies developed,and the eastern steep slope zone developed fan delta facies,with small area and only a small part of nearshore subaqueous fan.Tenger 2^ndsectionr period,the lake basin was in shrinking period and the water was retreating.A large amount of clastic materials was accumulated in the Western gentle slope zone to form braided river delta facies.In the eastern steep slope zone,fan delta facies,nearshore subaqueous fan and sublacustrine fan were mainly formed.Combined with the comprehensive analysis of well logging data,oil testing data,porosity and permeability data,and sedimentary facies diagrams,the Saidong sag develops fan deltas.The lithology of the distributary channel is mainly glutenite,which is an excellent place for oil and gas accumulation.The lithology of the distributary interchannel is mainly mudstone,which provides good sealing conditions for oil and gas,oil and gas shows good,high porosity,permeability.The lithology of nearshore subaqueous fan is mainly composed of glutenite and silty mudstone.Mudstone provides good conditions for oil-gas sealing of glutenite section,with high porosity and permeability and good oil-gas display.The lithology of lake facies is mainly mudstone and small-section sandstone,the porosity and permeability are extremely low,oil and gas are not easy to accumulate and preserve,and the oil and gas show poor.