Distribution Of Tight Sandstone Reservoirs In He8 Formation,Su 59 Gas Field,Ordos Basin

Sulige gas-area is located in the northwest of the Yishan slope in the Ordos and the fifty-nine block of Sulige is in the western part of the Sulige gas-area,gas and water production is a typical feature of the He-8 gas reservoir.The vertical superposition of the tight sandstone in He-8 is unclear,and the formation mechanism of high quality reservoirs in thick sandstone is still unclear,these are all the factors that restrict the exploitation of the Sulige gas-area,Therefore,it has a great significance to study the characteristics and distribution regularity of tight sandstone reservoirs.Based on core and thin section observation,logging data analysis and core analysis,etc.,following conclusions could be drawn:(1)The He-8 formation is a delta plain deposit,of which the He-84 is a braided river delta plain,the He-83 to He-81 is a meandering river delta plain deposit.The sand body of He-8 formation are superimposed in multiple stages,The superposition relationship of sand body in each sub-layer includes scour-cutting type,scour-contact type and continuous contact transition type,the main types are scour-cutting type and continuous contact transition type;(2)The tight sandstone of He-8 formation can be divided into four types of lithofacies:(gravel)coarse-grained lithofacies,fine-to medium-grained sandstone lithofacies,interbedded rippled siltstone lithofacies and dark grey mudstone lithofacies.The main common lithofacies consist of(gravel)coarse-grained sandstone lithofacies and fine-to medium-grained sandstone lithofacies,fine-to medium-grained sandstone lithofacies mainly deposited in a relatively low energy environment,such as the transverse bar or the top of a longitudinal bar with low energy.(Gravel)Coarse-grained sandstone lithofacies deposited in the channel and longitudinal bar with high energy.Interbedded rippled siltstone is also deposited in a relatively low energy environment.(3)The main diagenesis of He-8 formation is compaction,siliceous cementation,clay cementation,carbonate cementation and dissolution.The main diagenesis of the lithic sandstone is compaction and clay cementation,the main diagenesis of the lithic quartz sandstone is siliceous cementation and dissolution.(4)The rock property of tight sandstone reservoirs in He-8 formation are mainly controlled by lithofacies and the diagenetic differences between different lithofacies.(Gravel)Coarse-grained lithic quartz sandstone is high-quality reservoir in He-8 formation,and favorable reservoirs area have been predicted by combining the map of lithofacies distribution and the thickness map of lithic quartz sandstone.