The Research On The Main Factors Of Controlling The Development Of Ordovician Geothermal Reservoirs In Tianjin

As a new kind of green energy, geothermal resources can reduce theconsumption of traditional fossil fuels and are becoming increasingly popularbecause of the simple mining conditions and wide range of uses. Tianjin area hasrich geothermal resources. At present, the extractive geothermal reservoirs have poretype of reservoirs and bedrock fissure type of reservoirs in Tianjin. pore type ofreservoirs contain Neogene Minghuazhen and Guantao Formations, which weredeveloped unstably.Bedrock fissure type of reservoirs contain Ordovician System,Cambrian System and Wumishan Fm of Jixian System. Ordovician System,Cambrian System were developed unstably. Because of its stable developmentWumingshan Fm has become the main mingning layer. The heavy developmentintensity and concentrated mining has caused a rapid decrease in the reservoirpressure, so the development efforts of the Ordovician reservoirs need to be added.The top depth of the Ordovician reservoirs is882~3104m, the thickness of theOrdovician reservoirs is882~3104m, single well yield is mostly30~200m3/h, thewellhead stable flow temperature is48~76℃in Tianjin and the richness of the wateris not uniform. Because of the instability of the Ordovician reservoirs,theconstruction risk is high and the development progress is affected.By collecting more than50Ordovician wells’ drilling data, regional geologicaldata and the previous research results, this paper retranslate the logging curves,redivide the Ordovician strata, count up the fluid leakage and crack development,and identify the spatial distribution, attitude and the relationship of the upper andlower strata. This paper researches the main factors of controlling the developmentof the Ordovician reservoirs including lithology, structure, sequence combination,hydrodynamic condition, buried depth and so on. The increase in clay content has anegative influence on the karst development. The karst developed better in thestructural bulge area than in the sag, and the more close to the faults, the better thekarst developed. The karsts of the fault upperwall and the fault footwall which havethe same lithologic character are different. Drilling data shows that the karst of the fault upperwall developed better than the karst of the fault footwall developed. Whenthe overlying strata is the Neogene, the karst developed best because of the long timeof weathering and eluviations. When the overlying strata is the Mesozoic erathem,the karst developed secondly. When the overlying strata is theCarboniferous–Permian System, the karst developed thirdly. Numerous drilling datashows that the Majiagou Fm karst in Middle Ordovician developed best and theYeli-Liangjiashan Fm in Lower Ordovician developed worst. Fengfeng Fm inMiddle Ordovician had negative effect on the development of the lower karst.Because the drilling fluid leak easily in Ordovician reservoirs, especially theleak in weathered crust cause huge risk to the construction, the forecast of riskanalysis and respond measures must be done before drilling the Ordovician Systemto make the construction successful.