The Formation Mechanism Of Siliceous Cement In Coal Measure Tight Sandstones Of Taiyuan Formation,Linxing Area

According to the estimation of recoverable reserves of natural gas technology in China,the United States,Canada,Australia,India and other regions of the world,the recoverable reserves of natural gas surplus technology in the world in 2013 were 720 trillion cubic meters,of which the recoverable reserves of tight sandstone gas were about 54 trillion cubic meters.Over the past few decades,proven reserves of natural gas in the United States have continued to increase,largely due to unconventional natural gas,mainly tight sandstone gas.As far as China is concerned,tight sandstone gas is mainly distributed in the Upper Paleozoic Carboniferous-Permian in the Ordos Basin,and the study of the genesis mechanism of high-quality reservoirs has always been a hot issue in the field of tight sandstone gas reservoir research,and the tight sandstone reservoir of the Taiyuan Formation in the Upper Paleozoic Linxing area of the Ordos Basin has good exploration prospects,and the development of siliceous cement in the tight sandstone reservoir not only affects the physical properties of the deep reservoir,reflects the influence of diagenetic events,but also records the information of major geological changes in the burial process,which plays an important role in deepening the understanding of reservoir formation.Taking the tight sandstone reservoir of the Taiyuan Formation in the Upper Paleozoic Linxing area of the Ordos Basin as the research object,this thesis comprehensively uses core observation,thin section identification,scanning electron microscopy,inclusion temperature measurement and other testing methods,combined with the analysis of tectonic evolution history and buried evolution history,to systematically study the stage and characteristics of siliceous cementite,material source,material transport,precipitation process and its cause,and discusses the formation mechanism of siliceous cementite,and achieves the following results:The rock types of the upper Paleozoic sandstone reservoir in the eastern Ordos Basin are mainly rock chip sandstone,followed by rock chip quartz sandstone,rock chip quartz sandstone,rock chip feldspar sandstone and quartz sandstone,and the clastic particles are mainly quartz and rock chips,which can also be seen that the high content of siliceous cement is because the proportion of quartz in the clastic particles is relatively large.There are various types of diagenesis in Linxing area,which have obvious effects on the physical properties of the reservoir,and the compaction reduces the pores,but cementation is the main reason for the densification of the reservoir,and siliceous cementation is the key to reservoir densification.Siliceous cement is one of the widely developed autogenic minerals in the Taiyuan Formation in Linxing area of Ordos Basin,and the main types include quartz enlarged edge,autogenic quartz filling pores and microcrystalline quartz.In the Linxing area,quartz is commonly enlarged,and it is deposited in the form of single particle suspension and cementation of other particles;Autogenic quartz is mostly automorphicsemi-automorphic,occupying feldspar dissolution pores and granules,and forming later than quartz enlarged edges.The Taiyuan Formation sandstone reservoir in the Linxing area has developed two stages of siliceous cement.The first stage siliceous colloid production is quartz with large rim,formed by early quartz pressure dissolution and feldspar dissolution;the second stage siliceous colloid production is quartz with large rim,quartz microcrystals and pore-filled authigenic quartz,with the uniform temperature of brine inclusions at100-130℃;the uniform temperature of a small amount of brine inclusions is higher than 160℃.Sandstone reservoirs often undergo complex diagenetic evolution throughout the burial evolution process,and siliceous cementation shows multi-production and multiphase cementation in sandstone reservoirs.The development of siliceous cement is influenced by hydrocarbon charging,hydrothermal fluid charging and the composition of the rock itself.The first phase of silica cementation in Linxing area is from pressure dissolution and feldspar dissolution,and the second phase is mainly from feldspar dissolution and clay mineral transformation,and the development of "feldspar dissolution and clay mineral transformation as the main source of supply,multiple endogenous sources-single exogenous source,multi-stage cementation" silica genesis pattern.The reservoir is protected by a large amount of hydrocarbon filling before the precipitation of siliceous cement.