The Evolution of Ordovician Paleo-channels before 460 Million Years and Its Petroleum Geological Significance
Some oil-gas fields of large-scale have recently been discovered in marine carbonate in China, especially the significant discoveries in deep reservoir that had revealed a favorable exploration prospect. North Tarim area is the first-order tectonic unit of Tarim Basin, whcih was the only area that petroleum have been found at the depth of 5500-7000m in deep Ordovician carbonate reservoir of China. The reservoir was characterized by extra-low porosity, low permeability and strong heterogeneous. Distribution of reservoir was controlled not only by the high-energy sedimentary facies and corrosion in the early stage, but also the paleo-channels which were developed in carbonate platform playing an important role in optimizing and improving reservoir properties. This research discussed on how to recognize the paleo-channels according to 3D seismic data and seismic attributes, and the relationship between distribution of paleo-channels and distribution of deep reservoir capacity in deep Ordovician carbonate reservoir.
According to basic principles of seismic sedimentology, based on high-resolution 3D seismic, and combined with 3D visualization, coherence cube interpreting, stratigraphical slicing method, seismic frequency-decomposition and RGB frequency mixing comprehensively, paleo-channels which were developed before 460 million years were recognized in Halahatang, the second-order tectonic unit of north Tarim area. Characteristics of two periods of paleo-channels were depicted, which were respectively developed on the top of Ordovician and the bottom of Tumuxiuke formation of middle Ordovician. Paleo-channels on the top of Ordovician were confirmed as stable meandering, while the ones in Tumuxiuke formation were defined to meandering. Furthermore, they were all developed on the background of a relatively gentle geomorphology.
It was very meaningful to recognize paleo-channels in the bottom of Tumuxiuke formation. Firstly, this sequence surface was deemed as exposed unconformity by recognizing the paleo-channels, while it was thought as drowned unconformity; furthermore, it could proved the existence of karst; Secondly, distribution of paleo-channels were related with the fracture network previously formed. Karsting could be well developed around the channels, it means that the good reservoirs could be found along the paleo-channels.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California