鄂尔多斯盆地中东部二叠系太原组灰岩天然气成藏特征及资源潜力OA

The exploration breakthrough of the Hengshan Gasfield in the Permian Taiyuan Formation limestone,regarded as a non-effective reservoir in a long term,has demonstrated its significant accumulation potential in the central-eastern Ordos Basin.This study systematically analyzes the geological conditions controlling natural gas accumulation and reveals a"sandwich-type"accumulation model,in which the coal seams of No.5 in the Shanxi Formation and No.8 in the Benxi Formation respectively served as source rocks,directly contact the limestone reservoir,and a high source-reservoir pressure difference about 8–12 MPa drives efficient gas charging.Bioclastic shoals(porosity of 2.6%,and thickness of 4–10 m)and bioherms(thickness of 2 – 6 m,dissolution pores developed)are identified as high-quality reservoirs,with fractures and penecontemporaneous karstification jointly improving reservoir performance.By integrating the volumetric method,small-element volumetric method,resource abundance analogy,and basin modeling,the total in-place natural gas resources of the Taiyuan Formation limestone are estimated at 1.553 5×1012 m3,with the remaining unproven resources amounting to 1.544 7×1012 m3.The bioclastic shoal facies has the highest enrichment(about 53.1%of the remaining unproven resources),being the priority exploration target.This study provides a critical basis for increasing natural gas reserves and production in the Ordos Basin and for evaluating similar tight carbonate gas reservoirs.