| No substantial achievements have been made during the years of conventional oil and gas exploration in the south of Guizhou province,so in recent years,attention has been turned to the unconventional oil and gas resources.As a kind of unconventional oil and gas,shale gas is mainly composed of methane,which is mainly stored in the shale that is rich in organic matter and its interlayer in the way of absorption or dissociation.As is found in the study,the organic matter content of shale in the fire drying formation and the Dawuba formation of the upper Paleozoic is high,and is widely spread,which has great potential for development.However,for the reason that the dark shale in the southern part of China is mainly formed by marine facies and transitional facies of land and sea,the intergrowth between shale and carbonate rocks is the basic geological character of the Paleozoic,and the karst problem has always restricted the exploration and development of the shale gas.According to the comprehensive data such as drilling,logging and seismic data,this paper studies shale and carbonate rocks in contact with it as a whole through geological profile survey,old well review,geophysical exploration and some other methods and ways,so as to provide a new idea for the shale gas exploration and development in karst areas.It is considered in this study that the upper Paleozoic strata in the area of Yangba in the south of Guizhou are carbonate platform in the west,slope platform basin in the east,and platform edge in the middle,showing a banding distribution near the north and south direction.Combined with the field profile survey and the sedimentary facies plane distribution of the study area,the area where Fengting and Linna are located is divided into key research areas.The study found that the main target layers of organic-rich shale in the key research area are the gray-black marl of the middle-low Devonian fire-baked group,the black and yellow-brown shale of the Lower Carboniferous Dawuba Formation,and the carbon shale of the Nandan Formation.The organic matter has high maturity and strong hydrocarbon generation ability.The carbonate rock layers associated with the shale target layer mainly include the Wuzhishan Formation lenticular limestone,the Nandan Formation meteorite mudstone,and the Sidazhai Formation limestone.The upper Paleozoic karst strata in the study are divided into 2 types,4 types and 5 subtypes.Among them,the Sidazhai Formation is a medium-strong karst layer group,the second section of the Nandan Formation is a strong karst layer group,and the Nandan Formation and the fire-drying group are weak-medium karst layers.According to the strength of karst strata,karst spatial type division and testing,we determine that the four great zhai formation,the second number of Nandan formation and the limestone continuous karst formation are the sensitive layer of the shale gas drilling,while the first number of Nandan formation and the Wuzhishan formation are the shale reservoir-forming packers.Then according to the development of fractures in different tectonic positions,the folded wing is proposed to be a favorable area for the deployment of shale gas Wells.Two typical shale gas wells drilled in karst in southern China were analyzed,and the wells were selected to avoid strong karst formations.When the shale gas target layer contains multiple sets of dense carbonate interlayers,it is difficult to form a complex seam crack network.When the shale gas target top and bottom layers are strong karst layer groups,it is easy to cause the loss of fracturing energy and cause water pollution.It is easy to form a complex artificial network when it is a weak karst layer group.Combined with the ground karst conditions,ground mining conditions,structural conditions,deep karst aquifer development and hydrodynamic conditions,the shale gas exploration and development avoidance zone,sensitive zone and favorable zone are divided into the study area. |
