Upper Paleozoic tight gas sandstone reservoirs and main controls, Linxing block, Ordos Basin

The Upper Palaeozoic tight sandstone in the Linxing block at the east margin of Ordos Basin is estimated to have a great gas potential of over 100 BCM.However, complex gas-water distribution by highly heterogeneous reservoirs against a special structural background and changing reservoir-forming settings with controls hinder the gas exploration and development in the block.From a perspective of tight sandstone gas reservoiring conditions, this study starts from establishing lateral sedimentary models, analyzing the vertical coupling relationship between source rocks, reservoirs and cap rocks, to summarizing the gas-water spatial-temporal distribution pattern and differential characteristics of gas accumulation process.The differential enrichment law in the block revealed throught the study can be used to guide an effective release of the huge gas potential from the east margin of Ordos Basin.The configuration of source rocks, reservoirs and carrier beds is defined as that the coal-measure source rocks characterized by high organic matter abundance and hydrocarbon generation potential is connected vertically with the sandstone reservoirs of marine barrier-coast tidal flat facies and continental rivers-shallow delta facies via the moderately developed faults, thus vertically constituting three plays that can be described as lower indigenous play, middle near-source rock play and upper far-source rock play.The study proposes that tight sandstone gas reservoirs in the block are formed after tightening-up process based on a deeper understanding of tightening-up mechanism of sandstone reservoirs and the coupling relationship between diagenesis and reservoir-forming.It suggests that it is overpressure that drives the gas to migrate after analyzing the migration and accumulation mechanism.It establishes a quasi-continuous selective accumulation model of multi-layer systems in different structural zones with sufficient gas source.It also summarizes the main controlling factors of multi-layer system and boils down the characteristics of the reservoirs as "source rock controlling gas potential, structure controlling play, micro-phase controlling reservoir, and physical property controlling accumulation".It finally concludes that high volume of gas continuously gushed from source rocks would preferentially migrate to and accumulate in areas with the right faults and high permeability sand bodies as well as moderate tectonic activities. © 2021, OIL & GAS GEOLOGY Editorial Board. All right reserved.