Stratigraphic Characteristics Of The Tertiary Sequence Beneath The MXN Depression And Its Modelling

The MXN depression is located in the southeast of the Bozhong Depression in the Bohai Bay Basin,adjacent to the Jiao Liao uplift tectonic zone.The area is mainly controlled by the development of the Tan Lu strike-slip fracture and extensional fracture,and the geological structure of the area has a complex and variable nature due to the influence of various tectonic stresses during the development and deposition of the area.At present,the MXN depression is poorly explored and insufficiently studied.In order to correctly understand the stratigraphic characteristics of the Lower Tertiary in the MXN depression and its sedimentary phase types,and to better guide the exploration for oil and gas in the Lower Tertiary,this paper applies the principles of stratigraphic stratigraphy and sedimentology to delineate the Lower Tertiary stratigraphy and identify the sedimentary phase types based on the existing regional sedimentary geological research understanding,logging and 3D seismic data.The spatial distribution characteristics are summarised to deepen the understanding of the stratigraphic and sedimentary system of the Lower Tertiary in the MXN depression.The deposition process of the stratigraphic sequence was simulated and analysed in Dionisos,a sedimentation numerical simulation software.Through the above studies,the following insights were obtained in this paper:1.The Lower Tertiary in the study area can be divided into three secondary sequences and five tertiary sequences.The tertiary sequences are SQ1,SQ2,SQ3,SQ4 and SQ5 in order to establish a stratigraphic framework.The southern part of the study area has the greatest sediment thickness and is the initial sedimentation centre of the depression.The sedimentation centre is characterised by south to north migration due to the influence of both strike-slip and extensional fractures.2.Based on the analysis of single and continuous well phases in the study area,combined with seismic phases,the main types of Lower Tertiary sedimentary systems were identified:braided river delta,fan delta and lake sedimentary systems.The fan delta,with its near-source,short-range transport development,was widely developed during the initial stage of the lake basin formation;the braided river delta,with its near-source development,long-range extension and large lateral extension development,was widely developed during the late lake basin formation;the lake sedimentary system was developed throughout the basin formation.3.Numerical simulations with Dionisos controlling a single variable reveal that changes in slope and changes in lake level have an important controlling role on the depositional processes of the stratigraphic sequence.As the slope of the depositional environment increases,sediment is deposited rapidly from the source into the basin;as the slope decreases,sediment accumulates at the source and the thickness of the stratigraphy in the basin is thinner than at high slopes.Accretion increases as the lake level decreases and accretion increases as the lake level increases.