Study On Sedimentary Model Of Tide-dominated Estuary Reservoir Based On Sedimentary Dynamics

Block Q in Oriente Basin,Ecuador,South America is rich in oil and gas resources.The sand bed of Cretaceous N1 layer is the main reservoir.Affected by the paleocontinental sea of South America,the N1 layer of Q block develops tide-dominated estuary sedimentary facies.Due to the dual influence of fluvial and tide flow,the sedimentary model of N1 layer is complex sand bed.In this paper,a detailed studies of the stratigraphic division and correlation,sedimentary facies analysis,sedimentary dynamics numerical simulation and flume experiment of N1 layer are carried out.A three-dimensional sedimentary model of tide-dominated estuary reservoir in N1 layer are summarized and constructed.On the basis of the above,a three-dimensional geological model controlled by the sedimentary model is established using the multi-point statistical(MPS)modeling method,and the superposition relationship and distribution of sand bed in tide-dominated reservoirs are described in detail in three dimensions.The above research results lays the foundation for the efficient development of N1.Stratigraphic division and sedimentary facies of N1 layer are carried out based on logging and core data.The results show that N1 layer includes two fourth-order sequences(N1-ZONE layer and N1SS layer)and four fifth-order sequences(N1-ZONE,N1SS-1,N1SS-2 and N1SS-3).The N1-ZONE layer mainly develops shelf mudstone facies and becomes a natural barrier between N1 layer and its upper Basal-Tena.The N1SS is mainly sandstone layer with tide-dominated estuary facies.The N1SS layer developed includes tidal sand flat,tidal sand bar(main body,edge)and’mudstone wall’(i.e.,tidal channel filled with argillaceous)sedimentary microfacies.Based on the analysis of sedimentary facies,a detailed numerical simulation of sedimentary processes is implemented.Six factors including water depth,discharge,slope,sediment grain size,estuary opening angle and tidal height is carried out,according to the tide-dominated sedimentary characteristics of N1 layer.The optimal simulation parameter combination is determined by analyzing and comparing with the actual distribution characteristics of sand bar.The results show that:(1)with the increase of water depth,the number of sand bar and the thickness of interlayer decrease,while the length-width ratio increases;(2)with the increase of discharge,the number of sand bar decreases,the length-width ratio,deposition thickness,and the interlayer thickness increase;(3)with the decreases of terrain’s slope,the number of sand bar increases and the length-width ratio increases;(4)with the decreases of gain size,the number of sand bar decreases,the length of sand bar also increases,and the interlayer is become thicker and longer;(5)with the increases of opening angle of estuary,the number of sand bar and the interlayer thickness are both increase,while the average width of sand bar decreases;(6)with the increase of tidal height,the thickness of the sand bar decreases,the bar number increases,the length-width ratio increases,and the thickness of the interlayer decreases and the length increases.The optimal combination of simulation parameters is that the bed slope is 0.017°,the discharge is 3000 m~3/s,the tidal height is 6.8 m,the water depth is 8 m,the mouth bay opening angle is between 60°and 120°,and the sediments include 125μm and 80μm sand and argillaceous.Based on the similarity principle,using flume experiments to verify the optimal simulation parameter combination and characterize the sand bed.The results show that the heart shaped sand bar,axe shaped sand bar and long axis shaped sand bar are developed in the flume experiment.There are many fine-grained muddy deposits on one sides of the sand bar,and a strip of fine-grained muddy deposits are formed in the waterway.The results of the flume experiment are highly similar to the numerical simulation results.The flume model can reproduce the deposition pattern similar to the numerical simulation.Combined with stratigraphic division,sedimentary facies and sedimentary dynamics methods,the three-dimensional sedimentary model map of the study area is established.Based on the three-dimensional sedimentary model,the three-dimensional geological model is established by using multi-point geostatistical modeling method.The results show that the tidal sand flat is stable and developed in the whole region.The main body of the tidal sand dar is small and distributed alternately with tidal sand flat.The deep-cut sand flat facies of the tidal channel forms a local deep-cut groove,and the groove is filled with mud in the low current energy period,forming"mudstone wall"(ie,tidal channel filled with mud).The lithology model shows that the shale content of N1-ZONE layer is high,the sand continuity of N1SS layer is fine,and the mud content is low.The attribute model shows that the porosity and permeability of N1-ZONE layer are both low,the reservoir property of N1SS layer with high porosity and permeability is fine.