The Discovery Of Cold Seep Carbonate In Biluocuo Region, Qiangtang Basin And Study Of The Formation Conditions Of Gas Hydrate

BiLuocuo region is located in the North Central Qiangtang depression ofQiangtang basin, north from BiLuocuo, south from DeRucuo, west from Amuzaipu,east from Jiunai, covers an area of600km2. The study area’s formation is mainly theJurassic strata, and formation development is complete, huge sedimentary thickness,good potential of hydrocarbon, Buqu Formation is the best source rocks in theQiangtang basin currently found, and its development is now known the best dolomitereservoir properties, with a relatively good source-reservoir-cap combination. Themain purpose of this paper is based on the discovery of gas hydrate geologicalanomaly flag such as cold seep carbonate of the experimental investigation. Based ontaking the suspected “cold seep carbonates” sample, raw oil samples, reservoirsamples,etc., which collected from the BiLuocuo region, for inclusion of thetransmitted light and fluorescence observation, carbon and oxygen isotopes, residualorganic carbon TOC, chloroform bitumen”A”, rock high temperature pyrolysis totalhydrocarbon yield, organic maceral, kerogen isotope, ethnic component analysis andother tests, combined with previous studies in the context of regional geologicalstructure, discusses the formation conditions of gas hydrate in BiLuocuo region. Andmade the following main understanding:1. After taking four suspected “cold seep carbonate” form Buqu formationcarbonates for microscopic observation and carbon and oxygen isotopes, it isidentified the cold seep carbonate, which is also an important indicator of leakage ofgas hydrates in this region;2. Through geochemical analysis, we found the Quse formation has the highestabundance and the best type of organic matter, in mature/high mature stage, withgood hydrocarbon potential; Buqe formation’s abundance of organic matter in general,basically at the mature stage. Sewa formation’s and ShaQiaomu formation’shydrocarbon potential are very limited;3. Buqu formation’s carbonate reservoir space is dominated by denudation pores and cracks, pore throat structure is mesoporous-fine throat, the average porosity is8.07%, average permeability is44.06×10-3μm2, belongs to the med/low-porosity andmed/low-permeability reservoirs. Observation under microscope showed that thereservior property of Buqe formation’s dolomite, oolitic limestone are good,denudation pores and cracks’ hydrocarbon are also good, and possibility of gashydrates existence in Buqu formation is higher;4. Capping layers in the study area, developed dense sets by the Quse formation,Buqu formation, Xiali formation of plate mudstone, gypsum salt rock, marlstone, clayceramics limestone. Development of large thickness, better sealing property.Neotectonism in the study area mainly for the uplift block difference, relative to theinternal calm, made less destructive to oil and gas reservoirs (including natural gashydrate). At the same time, the Qiangtang basin was low heat flow cold basin, havelower geothermal background, it’s beneficial to the formation of gas hydrate, thesuitable depth for the hydrate is about50-1000m. Thus we believe that BiLuocuoregion do have the formation conditions of gas hydrate.