The formation and distribution of deep weathering crust in north Tarim basin.

Carbonate weathering crust karst reservoir is developed in Tabei area, with the features of high quality, widely distributed and deeply buried, and several giant oil and gas fields, with trillion tons of oil and gas resources, have been discovered in Lunnan, Tahe and Yingmaili area. Based on system analysis of drilling, logging, oil testing and other first-hand data of over 200 important wells, combined with substantial testing data and cores microscope observations, fine studies of the weathering crust reservoir genesis, distribution, prediction and evaluation have been carried out. Studies suggest that in the Cambrian dolomite weathering crust reservoir was developed, mainly pore-cave type; While in the Ordovician it' s mainly limestone weathering crust reservoir, with lower matrix porosity, and corrosion holes, corrosion expansion fractures and construction fractures were the main reservoir space, mainly cave-type reservoir and reticular fractured reservoir. Development of pure platform facies carbonate rocks, long-term exposure and erosion of formation caused by Hercynian tectonic movement, fracture fissure and late atmospheric leaching of fresh water are the important controlling factors of the weathering crust reservoir formation. And find that weathering erosion mainly occurs in the depth of less than 140m in Tabei area. Although the matrix porosity of weathering crust reservoir is poor, the depth has little effect to reservoir properties; in favorable paleokarst landforms and fracture zones, even in a greater burial depth, the reservoir of a larger scale, and better performance may also be developed.