摘要
Calcarenaceous sandstones are generally believed to be tight and thus non-reservoirs.In February 2012,after well test was done on the X7 well in the YB area of the Sichuan Basin by the Sinopec Southwest Branch Company,a high-rate industrial gas flow was obtained in the 3rd member of the Upper Triassic Xujiahe Formation.Thin-section observation showed that the reservoirs are mainly composed of calcarenaceous sandstones.Based on the comprehensive analysis of the petrophysical features,reservoir space characteristics,poroperm characteristics,electrical properties,and seismic responses,a gas accumulation pattern is recognized,i.e.,calcarenaceous sandstone distribution plus favorable diagenesis(early short period exposure and dissolution and late organic acid dissolution) plus structural fracture development zone plus suitable timing of faulting.Reservoir prediction was also made through the integrated analysis of sedimentary facies,seismic attributes,and fracture distribution.It shows that hydrocarbon accumulation mainly occurs in the areas where both calcarenaceous sandstones and structural fractures are highly developed.Proposals were presented for the emplacement of three wells based on these understandings.