Ultra-deep dolomite types and their reservoirs potential of the Ordovician Yingshan Formation in Shunbei area,Tarim Basin
Dolomites of the Ordovician Yingshan Formation,which exhibit significant exploration potential,are found in the Shunbei area of the Tarim Basin.However,there is no systematic explanation on the genesis and physical property variations of the stratified dolomite in this region.Based on detailed petrology observation,carbon and oxygen isotopes,rare earth element analysis,carbonate U-Pb chrono-logy dating,and porosity and permeability testing under different stress states,this study discussed the types and genetic mechanisms of the inner stratified dolomites of the Yingshan Formation.Furthermore,it provides a preliminary evaluation of the differences in physical properties among dolomites of various origin.The findings can be summarized as follows:(1)The relative development of dolomites in the lower part of the Yingshan Formation located in the northern region of Shunbei area primarily consists of two types of stratified dolomites,including the buried pressure-dissolved dolomite(Class Ⅰ)and the penecontempora-neous seepage reflux dolomite(Class Ⅱ).(2)The Class Ⅰ dolomites,which are predominantly distribu-ted in low-energy sedimentary facies,have their origin in burial dolomitization.This is attributed to the ge-netic mechanism of clay mineral transformation,driven by the formation of stylolites during the burial process.These dolomites are relatively more developed in the central part of the Shunbei area.(3)The Class Ⅱ dolomites are characterized by penecontemporaneous seepage reflux dolomitization in sedimentary facies that display high geomorphology and relatively high energy.These dolomites are primarily distributed and well developed in the western and southern Shunbei area.(4)The measured physical properties of Class Ⅰ dolomites(φ:0.3％～1.0％;K:0.003×10-3～0.074×10-3 μm2)are lower than those of ClassⅡ dolomites(φ:0.4％～2.0％;K:0.009 × 10-3～0.055 × 10-3 μm2).However,ClassⅠ dolomitescan enhance the ratio of dolomite-limestone interbedding,and there are fractures to transform into reservoir po-tential.This study is of significant reference value for ultra-deep dolomite oil and gas exploration in the Shunbei area of the Tarim Basin.
万方数据
维普
