Origin of Extra Low Porosity and Permeability High Production Reseroirs: A Case from Bashijiqike Reservoir of Dabei 1 Oil Field, Kuqa Depression
特低孔特低渗高产储层成因机制—以库车坳陷大北1气田巴什基奇克组储层为例

Reservoirs of the Cretaceous Bashijiqike Formation in the Dabei area of the Kuqa depression are dominantly lithic sandstone with a little feldspar-lithic sandstone, and mostly fine-middle grains, with 2%~10% iron-mud and mud, 3%~15% calcite cement. Clay minerals are mostly illite, chlorite, and illite-smectite (15%~20% smectite), and have no kaolinite. The main pore types are emposieu-primary pores (50%~90%), followed by micropore and tectoclase, and the reservoirs generally belong to low porosity-permeability and extra-low porosity and permeability. Comprehensively analyses show that episodic thrusting-overriding tectonism had an utmost importance in controlling the sediment cycle, alteration of water salt and distance from provenance. Origin mechanisms of extra-low porosity and permeability reservoirs are: poorly sorting middle-and coarse-stones formed in fan delta front during tectonically active time, high content debris formed by proximal and quick deposit, high carbonate cement formed in dry saline lake, relatively deep burial in early diagenesis and quick deep burial and compaction in later diagenesis. High productive reservoirs are the synergistic effect of well sorting fine-and middle-stones formed in braided river delta front during tectonically calm time, early regressive corrosion and poor carbonate cement, later tectonic disruption.