Sedimentary Microfacies And Reservoir Description In Tidal-dominated Estuary Of M1 Formation Of A Oilfield,Oriente Basin

The research area A oilfield is located in the northwestern part of the T block of the Oriente Basin.It is mainly composed of formation lithologic traps under low-amplitude structures' control.The main oil-producing layer is the M1 interval.At this stage,the development of the M1 layer in A oilfield has entered a stage of high water cut.This means that more detailed research is quite necessary,especially for the subsequent secondary development.Therefore,this paper conducts more detail research on the M1 interval of A oilfield from high-resolution sequence stratigraphy,sedimentary microfacies,reservoir description(?)The stratum of this study is the M1 sandstone of the Cretaceous Napo group This paper regards high-resolution sequence stratigraphy as the guiding ideology According to the change of the lithological surface and the amplitude of the log curve,the sequence interface is divided into four small layers:M1-Zone,M1SS-1,M1SS-2 and M1SS-3,and then the lateral and vertical direction of the M1 interval is established The results show that the sandstone thickness in the direction of the source is thinner toward the basin and the ductility is good,while the thickness of the sandstone in the vertical source direction is relatively uniform.(?)The M1 interval sedimentary period is a tidal-dominated estuary environment with sea-land interaction.The following three sedimentary microfacies are developed(a)tidal sand bar microfacies,mainly composed of medium-fine sandstones,showing a variety of interlaced bedding and lenticular bedding and double clay layer,the GR curve shows a box-shaped low amplitude;(b)the tidal sand flat microfacies,consisting of fine sandstone and siltstone,mainly developing enveloping bedding and a small number of plate-like staggered bedding,the GR curve shows low tooth-liked amplitude;(c)mixed flat microfacies,composed of siltstone and silty mudstone interbeds,mainly developed with horizontal bedding and biologic trace fossils.Besides,the M1 interval has experienced three stages of sedimentary environment:the delta-tidal-controlled estuary sedimentary environment,the tidal-dominated estuary sedimentary environment,and the shallow-sea continental shelf sedimentary environment.(?)This reservoir description is carried out from two aspects:reservoir inversion prediction and reservoir geological modeling.(a)Reservoir inversion prediction:Because the M1 interval is a heterogeneous thin reservoir with the development of a argillaceous interlayer,this study used a waveform phased inversion method to exploit the same characteristics of seismic waveforms and logging curves.(b)Reservoir geological modeling:This study introduces constraints such as reservoir unit thickness map,sedimentary microfacies plane distribution map,and reservoir prediction inversion results in the modeling process,and successively established layer models,petrographic models and physical properties.The model shows that the tidal sand dam has the best physical properties,and the average pore,permeability and saturation are 25.33%,2.7D and 76.55%,respectively.