Study On Logging Evaluation Method Of Total Organic Carbon Content And Vitrinite Reflectance In Shale Gas Reservoir

With the increasing demand for oil and gas resources in the world,conventional oil and gas resources are difficult to meet international needs,and shale gas,which is an unconventional oil and gas resource and belongs to clean energy,has received more and more attention.With the continuous development of theoretical research and exploration and development technology,shale gas has become the focus of the world.Total organic carbon content and vitrinite reflectance are important parameters to reflect hydrocarbon generation potential of source rocks and evaluate the exploit-ation value of shale gas reservoirs.In this paper,it is found that the lithology,physical properties,mineral composition and geochemical characteristics of shale reservoirs are all responsive to the logging curve.Therefore,for shale gas reservoirs with complex lithology and mineral composition,it is difficult to accurately calculate the total organic carbon content and vitrinite reflectance by using the logging curve.In this paper,the total organic carbon content and vitrinite reflectance are evaluated by different methods in order to obtain more accurate evaluation methods of geochemical parameters.Taking the Jiaoshiba area in southeast Sichuan as an example,combined with well logging data and core analysis data,this paper completes the lithological characteristics,mineral characteristics and geochemical characteristics of shale gas reservoirs in the study area through statistical analysis method.Based on the investigation of geochemical parameters evaluation methods for shale gas reservoirs at home and abroad,according to the mineral characteristics and the logging response characteristics of shale reservoirs in the study area,different methods are used to establish total organic carbon content and vitrinite reflectance evaluation model,using correlation analysis and error analysis to analyze the applicable conditions and application effects of each method.The shale gas reservoirs in the study area are mainly composed of dark gray silty mudstone and gray black carbargilite.The rock minerals are mainly composed of siliceous minerals and clay minerals,among which the clay minerals are mainly illite and imonte mixed layers.The average content of organic matter is up to 2.343%,which is a rich organic source rock.In terms of logging response,the shale gas reservoir as a whole shows the characteristics of "high gamma,high acoustic time difference,low density,high resistivity and high neutron".However,in some shale gas reservoirs,the resistivity presents a low value and a saw-toothed change,and the acoustic time difference does not change much compared with the non-hydrocarbon source rocks.Total organic carbon content evaluation method: curve fitting method can quickly determine the calculation model,but it has strong dependence on core data;traditional ?LgR method is only applicable to “passey” rock with LOM between 6~10.5;Improved ?LgR method reduces the influence of lithology,but still has poor evaluation effect on non-passey rocks.The radioactive curve stacking method is mainly affected by the sedimentary environment.The GR-KTH curve overlap method is suitable for marine sedimentary environment,and is not affected by clay minerals,conductive minerals and reservoir fluids.It is better than ?LgR method.GR-clay clay indication curve overlap method is applicable to source rocks containing no or a small amount of feldspar,which is less affected by other factors and has better effect on the evaluation of total organic carbon in the study area than other methods.The method of vitrinite reflectance evaluation: curve fitting method has a strong dependence on data and can quickly establish calculation model;?RRS method establishes calculation model by logging curve according to the geological significance of organic matter maturity,which has a wide application condition and good application effect.