Genetic mechanism and development model of dolostone reservoirs of the second Member of the Ordovician Majiagou Formation in the central-eastern Ordos basin
The dolostone in the second Member of the Ordovician Majiagou Formation in the central-eastern Ordos basin holds significant potential as a natural gas exploration target.However,a comprehensive understanding of its reservoir characteristics and genesis is still not clear enough,which restricts the next exploration deployment of this stratigraphic unit.This study systematically investigates these aspects using data from cores,thin sections,industrial CT scans,U-Pb dating,physical property analyses,and geochemical characterization.Based on these findings,a development model of dolostone reservoirs in this formation is established.The results show that:① The dolostone reservoir is mainly composed of gypsum nodule-bearing powder crystal dolostone,oolitic dolostone,gravel dolostone,and porphyritic powder crystal dolostone.Reservoir porosity is accommodated by gypsum mold pores,intergranular pores,intergranular dissolution pores,and microfractures.The average porosity of reservoirs lacking halite filling is 8.71％.② Favorable sedimentary microfacies and diagenesis,such as gypsum cloud flats,particle beaches,and biological disturbances,provide the basic conditions for reservoir development.Quasi-syngenetic dissolution and structural fracturing further enhance porosity through the development of dissolution pores and microfractures.Dolomitization contributes to pore preservation and enhancement in porphyritic powder crystal dolostone,while halite filling leads to reservoir compaction.③ The interplay between ancient tectonic patterns and sea-level fluctuations significantly influences reservoir porosity development and evolution.Favorable reservoirs are mainly preserved in gypsum-bearing cloud plains and granular beaches located outside the salt rock boundary or in porphyritic powder crystal dolostone units within the salt rock boundary.
Ordos basinthe second Member of Majiagou Formationdolostone reservoirsedimentary microfaciesdiagenesispaleotectonic patternsea level changes
万方数据
维普
