Application Of Organic-rich Shale Exploration Using Electromagnetic Method

In recent years,along with the need for green low-carbon economy and the increasing demand for clean energy,Unconventional oil and gas resources become the focus all over the country,shale gas exploration grows fast,especially the development of shale gas in North America has changed the pattern of energy supply today.The shale gas resources in China have enormous potential,mainly lied in the Paleozoic marine,Mesozoic and Mesozoic continental basins,which has been proved in studies.As China's Mesozoic red beds distribution of the most concentrated area,Sichuan Basin is rich in oil-gas,there are two sets of marine high quality source rocks in the Lower Paleozoic,now It becomes the important area for shale gas exploration in our country.The research area is located in Junlian,Sichuan,Inner well showed,The development of black shale in Longmaoxi group has high abundance of organic matter,high maturity,slight fissure development,moderate burial depth,and favorable conditions for forming shale gas reservoir.Moreover the new two-dimensional seismic data indicates the stratigraphy is gentle and tectonic intact,it is far away from the treadmill fault,and the preservation condition is good,which is benifitical to shale gas exploration.By collecting the physical properties in the study area,we find the shale formation,especially rich organic,show a low density,low resistivity and high polarization characteristics compared with the surrounding rock.After data processing and inverting,the underground electrical structure model in surveying area,and combination with geological and geophysical data,the result shows there are five layers Electrical structures in the study area,that is Lower Triassic,Permian,Silurian,Ordovician-Cambrian and Precambrian.the Lower Triassic is further divided into the Triassic Jialing Group and Feixianguan Group.Magnetotelluric is conducive to reflect deep structure,controlled source audio-frequency magnetotelluric method is good in reflecting the shallow fine structure,once both combined,accurate electrical structure in the deep part of the surveyed area can be obtained.Using the resistivity inversion data of MT method and physical parameters of other methods in the study area,combined Zhao 104 well resistivity curve in study area with TOC data,this study established a neural network predict model of reservoir,results shows The predicted value of TOC is positively correlated with the measured value,It also is indicated that the content of TOC is related to polarizability and resistivity and it is worth exploring the non seismic data to identify the gas content in shale formation.