The Experiment Research Of CO₂-Sedimentary Tuff And CO₂-Tuffaceous Sands Interaction

A series of experiment were carried out by using the FYX-1type autoclave to investigate theinteractions between CO₂fluid and sedimentary tuff, tuffaceous sands under different temperatures.There main purpose of this research was interpreted the dissolution and the formation of the authigenicminerals, which were caused by interactions of CO₂fluid with pyroclastic rocks, and then setted up theinteraction mode of CO₂fluid with pyroclastic rocks.Throuth the petrologic characteristic analysis and the interaction experiments between CO₂andvolcaniclastic rocks, the corrosion, dissolution and generation of new minerals after CO₂fluid injectedwas discussed, and the interactions characteristic between pyroclastic rocks and CO₂were interpreted,furthermore the interaction mechanism between CO₂and pyroclastic rocks was clarified.The experimental samples include the sedimentary tuff and tuffaceous sands. The sedimentary tufffor the experiment were collected from the Shangkuli group of Shangkuli region in Labudalin basin（Location E:120°28’, N:50°14’）, which mainly consisted of crystal pyroclast and debris, and thediagenesis types were mainly compaction, cementation, devitrification and alteration. The tuffaceoussands were collected from Yixian group of Xijian mountain in Xingcheng（Location E:296677.10,4491022.40）, which were medium-grained tufaceous debris sandstone, and the diagenesis types werecompaction, cementation and metasomatism, alteration.Based on the interactions experiments between CO₂fluid and pyroclastic rocks, the resultsindicated that the corrosion intensity of feldspar, quartz and pyroclastic materials increasedaccompanied by the temperature increased, and with the same condition, the corrosion intensity of pyroclastic material was greater than the feldspar did. The corrosion for quartz grains began at150℃.The results showed that the K+in the reacted solution mainly came from the dissolution ofK-feldspar, the Ca²⁺and Mg²⁺were mainly connected with the dissolution of pyroclastic materials,eventually they combined with HCO-3to induced the generation of calcite and dolomite. Tfe mainlycame from the Fe-rich pyroclastic materials, such as neutral-basic volcanic debris, and finallycombined with HCO-3to generate siderite. Aluminum ions mainly came from the corrosion anddissolution of feldspar, which can exist with different forms in different pH, and finally form boehmitewith dehydration. SiO₂came from a variety of sources including corrosion and dissolution of quartz,feldspar and pyroclastic materials.By comparing the research with previous studies, it can be confirmed that the mass loss for tuff,sedimentary tuff, tuffaceous sands were decreased gradually after CO₂injected, and the corrosion anddissolution turned weaken successively. This phenomenon means that the intensity of pyroclastic rocksinduced by CO₂fluid injection has a great relationship with the contents of pyroclastic materials, whichshowing that with more pyroclastic materials, the dissolution and corrosion induced by CO₂injectionwould be stronger. After the experiment, the authigenic minerals are boehmite, iron oxide, kaolinite,siderite, calcite and dolomite.