Sedimentary characteristics and evolution of Upper Triassic Xujiahe Formation,northeastern Sichuan Basin
The exploration and development of tight gas for the Upper Triassic Xujiahe Formation in the Yuanba and Tongnanba areas of northeastern Sichuan Basin have achieved stable growth in production and reserves.However,there have been few important break-throughs in the adjacent southern area,due to the low exploration level and lack of systematic and detailed research on sedimentary fa-cies.Based on logging identification,logging lithology analysis,field outcrop investigation,and drilling core observation,a systemat-ic study was conducted on the sedimentary characteristics and evolution of the Xujiahe Formation in northeastern Sichuan Basin.The results are shown as follows.(i)The Xujiahe Formation is a braided river delta plain subfacies,which can be further divided into dis-tributary channel microfacies and distributary interchannel microfacies.The latter is dominated by swamp sediments with fine grains,which are mainly mudstones and shales.The former is chiefly composed of channel bar and channel filling sediments with coarse grains,which are mainly fine-medium sandstones.(ii)These sediments mainly came from the southeast provenance.And controlled by the provenance direction,the sedimentary facies zone shows a spindle or banded distribution along the NW-SE direction.(iii)In the northeastern Sichuan Basin,the Xu2 and Xu4 Members belong to the braided river delta with high material supply,which dominatly develops distributary channel microfacies with extensive channel bar sediments;the Xu3 and Xu5 Members belong to the braided river delta with low material supply,which mainly develops distributary interchannel microfacies.
Northeastern Sichuan BasinXujiahe FormationBraided river delta plainDistributary channel microfaciesSedimentary evolution
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