Diagenesis and reservoir space types of alkaline lake-type shale in Fengcheng Formation of Mahu Sag, Junggar Basin, China

Using observations and descriptions of drilling cores, image logging, microscopic section, argon ion polishing field emission scanning electron microscopy, X-ray diffraction, and whole-rock trace element analysis, the study of shale reservoir diagenesis and space types in the Fengcheng Formation of the Mahu Sag was conducted. Considering the trace element contents and their ratios (Sr/Ba, V/Ni, Th/U, V/(V + Ni), U/Mo, and Sr/Cu), the Fengcheng Formation is formed in a dry and hot continental lacustrine basin with a paleoenvironment of saltwater and anoxic/lean oxygen conditions. The shale reservoirs of the Fengcheng Formation with the characteristic of multisource mixed sedimentation include terrigenous clastic, volcaniclastics, and carbonate rocks. Currently, the Fengcheng reservoir of the Mahu Sag is in the middle of diagenetic-stage B. The principal factors for reservoir densification are compaction, dissolution, carbonate mineral cementation, and clay mineral cementation. The Fengcheng Formation develops multiple reservoir storage space types, such as rock fractures, stylolites, and micro–nanoscale pore-throat systems. The macroreservoir space types include tectonic, induced, bedding, and dissolution–expansion fracture types. The microreservoir space types include microfractures, stylolites, and micro–nanoscale pore throats. The research showed that the Fengcheng Formation has tectonic fracture-pore systems (tectonic fracture-type reservoirs) and stylolite-matrix pore-tectonic microfracture systems (shale oil reservoirs), forming the shale oil preponderant charging channel network. Reservoir space type and its spatial distribution are the principal factors for shale oil accumulation of the Fengcheng Formation in the Mahu Sag.

Application of Tracer Test in Survey of Hydraulic Connection between Water Gushing and Fracture Water in Karst Tunnel – Taking Zhongjiashan as an Example

The field tracer test is dropping quantitative tracer materials in the entrance of ponor upstream and to monitor online concentration of tracer materials in the main export of underground river downstream, and then deduce the type of groundwater pipe and the source of supply according to the concentration. This thesis takes the landslide areas in highways across form Quanzhou to Nanning and in tunnels connecting Ji’an with Zhongjiashan in Lianhua (a town in Pingxiang) as the research object, explores the supply source of tunnel water, meanwhile uses three tracer materials of different nature, namely the fluorescein sodium, fluorescent whitening agent and rhodamine, to place 4 drop points and 3 receiving points within 20 square meters of the surveyed area, to conduct groundwater tracer test. The test shows that there is no obvious connection between tunnel water gushing and F5 fracture main ditch surface water as well as F5 tectonic fracture zone; Fault F2 has good conductivity, and the gushing water in the right hole in the import and export of tunnel is related with F2 fault tectonic fracture zone.