Research Of Alluvial Fan Reservoir Quality In Seventh Central Zone Of Karamay Oilfield

The reservoir quality of sand-gravel body within alluvial fan varies greatly.However,the reservoir quality mechanism and distribution pattern of alluvial fan are not clear,which affect the effective development of this kind of reservoir.Based on core data,logging data and laboratory analysis data,this thesis,taking the sand-gravel body of lower Karamay Formation in seventh region of Karamay Oilfield as an example,aims at solving the problems above,so as to provide reliable geological evidence for the development scheme of binary chemical flooding.Research shows that:(1)The lithology of alluvial fans sand-gravel in the study area mainly includes middle conglomerate,fine conglomerate,coarse sandstone,medium sandstone,and fine sandstone,etc.Among them,coarse sandstone and fine conglomerate have the best reservoir quality,while the middle conglomerate with coarser grain size and the middle sandstone with finer grain size have relatively lower reservoir quality.(2)The pore-throat model of the study area is very complex and can be divided into seven sub-types.Namely,uni-modal type(including uni-modal?,uni-modal?,uni-modal?,uni-modal?),bimodal type(including bi-modal?,bi-modal?)and multi-modal type.Based on pore structure mode classification,the reservoir quality is divided into four types.The reservoir quality of glutenite with uni-modal?pore-throat model is the best(?type of reservoir).The second best are resevoirs with uni-modal?and bi-modal?(?type of reservoir).The third best are resevoirs with uni-modal?,bi-modal?and multi-modal(?type of reservoir).The poorest reservoir is glutenite with uni-modal?(?type of reservoir).(3)The main factors controlling reservoir quality are rock fabric,mudstone fragments,weathered crust mudstone and boundary fault.The rock facies with high mudstone fragments,high clay content and poor sorted particles underwent strong compaction,results in a large loss of intergranular porosity.The cementation in calcareous sand-gravel body is derived from the weathered mudstone at the bottom and transmitted upward through faults from the bottom to the top.The strength of calcareous cementation in sand-gravel rock is related to the distance to the weathered mudstone and the boundary fault.(4)There are differences in the spatial distribution of reservoir quality in the study area.Vertically,the reservoir quality at bottom is worst because of calcareous cementation,poorer at top section,and the best at central section in S₇^3-1 layer which was deposited in the middle and lower part of braided channel.On the plane,along with the source direction,the particle size becomes thinner,the content of clay mineral becomes higher,and the mudstone fragments become more,so the reservoir quality becomes worse.The middle part of braided channel,or the intersection of two braided channels,has coarse grain size,large thickness,resulting high reservoir quality.At the edge of braided river,the reservoir deteriorates due to the fine grain size and high clay content.Close to the fault,due to the serious calcium cementation,the reservoir quality is poor.