Research On Micro-characteristic Of CH8Oil Reservoir Of Yanchang Formation In HuaQing Area Of The Ordos Basin

This paper goes on to research and discuss the characteristics of petrology, microscopic reservoir characteristics, diagenesis and reservoir physical properties. In this process,this paper analyses this points by means of methods under the guidance of sedimentology, reservoir sedimentology and oil geology. The methods include the detailed description and observation of drilling cores, and observation of thin-section of the cast, measurement of homogeneous temperature for inclusions, analyses of X-ray diffraction, cathode luminescence image, electron scan microscope, and capillary pressure. After the comprehensive research of reservoir, It is of important theoretical value and guiding significance of exploration arrangement for oil and natural gas. After the comprehensive research of reservoir, the paper holds that:The componential and textural maturities of the sandstone in Yanchang formation is lower and lithological types are mostly fine-grained arkose, which the interstitial matter is widespread but not uniform distribution. The type of cements obsedved including carbonate, clay minerals, feldspar overgrowths, and a few laumonite, ferruginous cement. Diagenesis types include compaction, cementation, metasomatism, dissolution and fraction. The sandstones have experienced a diagenetic evolution from early diagenetic phase to later diagenetic phase. The dianenetic sequence being as follows:mechanic compactionâ†'authigenic clay rim (chlorite)â†'(early diagenesis) carbonnate cementationâ†'organic acid fluid injectedâ†'feldspar, detritus and carbonate dissolutionâ†'autogenous kaolinite formation,quartz overgrowthsâ†'illite montmorillonite mixing layer (or chlorite/montmorillonite mixing layer)â†'hydrocarbon emplacementâ†'(later diagenesis) Iron calcite precipitationâ†'Dolomite filling and metasomasis clastic part According to the characteristics of diagenesis the lithogenous phase is made. The authigenic clay rim (chlorite) and feldspar dissolution diagenetic phase is considered as advantage diagenetic phase.Pore spaces always occur as the combination form, and are mainly of the primary intergranular pores. The secondary dissolution pore takes a second place. The secondary pores of the sandstones were formed by the dissolution of the alumino silicate, tuffaceous interstitial material and carbonate minerals effect by the carbonic acid and organic acid produced in late diagenesis stage.The Pore assemblage types include Dissolution pore-Intergranular pore, micropore.The reservoir physical properties show that the porosity value is from6%to9%, the permeability value is from0.1×10-3μm to1.5×10-3μm.The reservoir is characterized by low porosity and low permeability and heterogeneity is very strong. Compared with other regions of Orods basin, the quality of reservoir is more densify.High-quality sandstone reservoirs are common controlled by material source and mother rock properties, diagenesis and diagenetical facies. The chlorite+dissolution pore facies, and chlorite facies that distributing between the carbonnate cementation+hydromica facies and kaolinite+hydromica facies are the most profitable diagenetic zones for developing high-quality reservoirs. Micro-fractures on one hand make the pores connect, improve the reservoir quality of the sandstones. On the other hand, act as the role that transporting petroleum.