Weathering Crust Model and Recognition of Carboniferous Kalagang Formation (C_2k) Volcanic Rocks in Niudong Block, Santanghu Basin

Weathering crust reservoir of C2k volcanic rock was the significant target of oil and gas exploration in recent years in the Santanghu Basin of Tuha Oilfield. According to its petrology and the natural characteristics revealed by drilling and logging data, this crust of weathering can be divided in vertical into weathered clay layer (sedimentary cover), highly weathered detritus, (the upper belt of weathering crust), weakly weathered block layer (the bottom belt of weathering crust) and non-weathering rock (dense volcanic belt). Effective reservoir space is developed in highly weathered detritus and weakly weathered block layer. According to the pore origin of the volcanic rock reservoir and the relations of the hydrocarbon source rock and the volcanic rock, the pattern of the volcanic rock crust of weathering is that the group hydrocarbon source rock for the volcanic rock is in C2h, the upper of which is non-hydrocarbon source rock, reservoirs are dissolved pores and fissures, and the upper part of the rocks is caprock, which constitute a good source-reservoir-cap association. The recognition of the volcanic rock crust of weathering is significant for seeking volcanic rock crust of weathering reservoir in the Santanghu Basin.