Study On Pore Throat Structure And Seepage Characteristics Of Different Modes In Sandy Conglomerate Reservoirs Of Cretaceous Guyang Formation In The West Of Linhe Depression,Hetao Basin

The sandy conglomerate reservoirs with unique modal pore throat structure has fast deposition rate,mixed clastic particle size,resulting in its seepage characteristics more complex than conventional sandstone reservoir,which restricts the effective development of this kind of reservoirs.The Cretaceous Guyang formation in the west of Linhe depression in Hetao Basin is a sandy conglomerate reservoir with large reservoir thickness and rich reserves,which has a good development prospect.However,the micro pore throat structure is obviously different from the conventional sandy conglomerate reservoir due to the weak cementation characteristics.The pore throat structure and seepage characteristics between different modes are more significant.The accurate understanding of the modal pore throat structures of weakly cemented sandy conglomerate reservoir is a key problem to be solved in the development of this type of reservoir,which has important research significance.Based on the analysis of sedimentary background,the sedimentary characteristics of alluvial fan sandy conglomerate reservoirs are analyzed,the distribution characteristics of sand body are studied,and the distribution laws of lithology and physical properties are determined.The pore throat structures of different modes in weakly cemented sandy conglomerate reservoir are comprehensively characterized by different means of experiment.According to the multifractal characteristics of micro pore throat structure,the pore throat space in the sample is divided into three types,and the modal characteristics of micro pore throat structure in sandy conglomerate reservoir are quantitatively analyzed based on the volume percentage of the three types of pore throat space for the first time.Through nuclear magnetic resonance and oil-water phase permeability experiments,the seepage characteristics of sandy conglomerate reservoirs are studied.The seepage characteristics and production performance response laws of different modes of pore throat structures are analyzed,so as to lay a theoretical foundation for the next efficient development of the oilfield.The main achievements are as follows:(1)The reservoirs of Cretaceous Guyang formation in the west of Linhe depression in Hetao Basin are in the alluvial fan sedimentary environment of rapid deposition under arid conditions,with complex lithology,mixed clastic particle size and different pore throat size.Micro pore throat structure has modal characteristics,which can be divided into unimodal,bimodal and multimodal pore throat structures.(2)The reservoirs are significantly weakly cemented.Compared with the well cemented sandy conglomerate reservoir,the physical properties are better,and the diagenesis has little effect on the pore throat structure.The micro pore throat structures of weakly cemented sandy conglomerate reservoirs are mainly controlled by the size of sedimentary debris,and the pore throat structure of different modes is significantly different.(3)According to the multifractal characteristics of full-scale pore throat structure of sandy conglomerate reservoir,the pore throat space in the sample is divided into three types:macrothroats,mesothroats and microthroats.The essence of micro pore throat structure heterogeneity of weakly cemented sandy conglomerate reservoir is the composition difference of three pore throat spaces.(4)The root cause of the formation of modal pore throat structures is the mixed accumulation of clastic particles with different sizes,and the direct reason is the different combination of the three types of pore throat space.(5)The unimodal pore throat structure is mainly formed by the accumulation of silt-mud particles,which is composed of the pore throat space of microthroats.The pore throat structure is relatively homogeneous,the pores and throats are small,and the physical properties are poor.The bimodal pore throat structure is formed by the accumulation of sand particles and silt-mud particles.The pore throat space is mainly the combination of mesothroats and microthroats.Compared with the unimode pore throat structure,the pore throat heterogeneity becomes stronger,the pore and throat become larger,and the physical properties become better.The multimodal pore throat structure is formed by the mixed accumulation of gravel particles,sand particles and silt-mud particles.The pore throat structure is a combination of three pore throat spaces: macrothroats,mesothroats and microthroats,which large pores and throats are relatively developed,with strong pore throat heterogeneity and good physical properties.(6)The distribution of pore throat structures with different modes is mainly controlled by the sedimentary characteristics,from the inner zone of fan root to the middle and outer zone of mid-fan,and the pore throat structure gradually transits from unimodal to multimodal and then to unimodal.(7)The difference of seepage characteristics and production performance of weakly cemented sandy conglomerate reservoirs reservoirs with different modal pore throat structures are mainly controlled by the different combination of pore throat spaces: macrothroats,mesothroats and microthroats.The mulitimodal pore throat structure is mainly composed of the pore throat space of macrothroats and mesothroats.The pore throat is large,which make the multimodal pore throat structure with high seepage capacity,high productivity and slow productivity decline.The seepage channel of bimodal pore throat structure is mainly the pore throat space of mesothroats,and the seepage capacity and productivity is the second.The unimodal pore throat structure is mainly composed of pore throat space of microthroats.The pore throat is small,the seepage resistance is large,which make the the oil-water seepage capacity is poor,the productivity is low,and the productivity decreases rapidly.