塔东地区寒武—奥陶系碳酸盐岩沉积特征及演化规律

SEDIMENTARY CHARACTERISTICS AND EVOLUTION LAWS OF CAMBRIAN-ORDOVICIAN CARBONATE ROCKS IN TADONG REGION

随着勘探程度的提高,塔东地区寒武—奥陶系碳酸盐岩地层展现出良好油气勘探前景.根据碳酸盐岩沉积模式,通过岩石学特征、地震相、沉积古地貌解剖等研究,在塔东地区识别出盆地、广海陆棚、台缘斜坡、台缘礁滩、台缘浅滩、开阔台地、局限台地相等7种碳酸盐岩沉积相类型,指出塔东地区寒武—奥陶系碳酸盐岩沉积相具有三分结构特征：中部发育盆地相区,东部和西部发育台地相区及台缘相区.确定了下寒武统深水盆地——开阔台地,中—上寒武统（较）深水、浅水盆地——局限台地,中—下奥陶统浅水、深水盆地——开阔/局限台地沉积相组合序列及沉积体系展布特征,并结合相对海平面升降分析建立了塔东地区碳酸盐岩缓坡台盆体系—镶边台盆体系—远端变陡型台盆体系的沉积演化模式.指出台地边缘相发育礁滩储层、台缘斜坡相发育重力流沉积储层及局限台地内发育膏溶储层,是油气聚集的有利相带。

With the increase of the exploration degree,Cambrian-Ordovician carbonate formations in the Tadong region have shown the good exploration prospects in finding oil and gas.According to the carbonate depositional models and studies on the petrologic characteristics,seismic facies and sedimentary palaeogeomorphologic analyses,seven types of the carbonate sedimentary facies in the Tadong region are identified,including basin facies,continental shelf of wide sea facies,slope of platform margin facies,reef and beach of platform margin facies,shallow beach of platform margin facies,open platform facies and restricted platform facies,and moreover the typical trisection structural features are pointed out in Tadong Cambrian-Ordovician carbonate sedimentary facies：the basin facies develops in the central area,the platform facies and platform margin facies develop in the eastern and western parts.The sedimentary-facies sequential compositions and distributional characteristics of the sedimentary systems are made sure in Lower Cambrian deep water basin-open platform and Middle-Upper Cambrian deeper water and shallow water basin-restricted platform and Middle-Lower Ordovician shallow water and deep water basin-open/restricted platforms.Combined with the analysis of the relative sea level fluctuation,the sedimentary evolution models are established for the ramp platform-basin system-rimmed platform-basin system-distal steepening platform-basin system in the Tadong carbonate region.The favorable facies belts for the petroleum accumulation are the reef and beach reservoirs developed in the platform margin facies and gravity flow reservoirs developed in the slope of platform margin facies and gypsum soluble reservoirs developed in the restricted platform.