Electrical structure identification of deep shale gas reservoir in complex structural area using wide field electromagnetic method

To fully exploit the technical advantages of the large-depth and high-precision artificial source electromagnetic method in the complex structure area of southern Sichuan and compensate for the shortcomings of the conventional electromagnetic method in exploration depth,precision,and accuracy,the large-depth and high-precision wide field electromagnetic method is applied to the complex structure test area of the Luochang syncline and Yuhe nose anticline in the southern Sichuan.The advantages of the wide field electromagnetic method in detecting deep,low-resistivity thin layers are demonstrated.First,on the basis of the analysis of physical property data,a geological–geoelectric model is established in the test area,and the wide field electromagnetic method is numerically simulated to analyze and evaluate the response characteristics of deep thin shale gas layers on wide field electromagnetic curves.Second,a wide field electromagnetic test is conducted in the complex structure area of southern Sichuan.After data processing and inversion imaging,apparent resistivity logging data are used for calibration to develop an apparent resistivity interpretation model suitable for the test area.On the basis of the results,the characteristics of the electrical structure change in the shallow longitudinal formation of 6 km are implemented,and the transverse electrical distribution characteristics of the deep shale gas layer are delineated.In the prediction area near the well,the subsequent data verification shows that the apparent resistivity obtained using the inversion of the wide field electromagnetic method is consistent with the trend of apparent resistivity revealed by logging,which proves that this method can effectively identify the weak response characteristics of deep shale gas formations in complex structural areas.This experiment,it is shown shows that the wide field electromagnetic method with a large depth and high precision can effectively characterize the electrical characteristics of deep,low-resistivity thin layers in complex structural areas,and a new set of low-cost evaluation technologies for shale gas target layers based on the wide field electromagnetic method is explored.

Combined U-Pb SHRIMP and Hf isotope study of the Late Paleozoic Yaminue Complex,Rio Negro Province,Argentina:Implications for the origin and evolution of the Patagonia composite terrane

We have carried out zircon U-Pb SHRIMP dating and Hf isotope determinations on a biotite paraschist and on a tonalitic orthogneiss of the Yaminué Complex, and re-evaluate this complex in the broader context of the tectonic evolution of the Patagonia composite terrane. In the metasedimentary unit （msuYC）, the youngest detrital zircon dated at 318 ± 5 Ma （Mississippian/Pennsylvanian boundary） indicates a Pennsylvanian （or younger） depositional age. The three main age populations peak at 474, 454 and 374 Ma. Preliminary Hf isotope data for two detrital zircons （447 and 655 Ma） yielded ε（Hf） values of -0.32 and 0.48, indicating that their primary sources contained small amounts of recycled crustal components （of Calymmian age; TDM 1.56 Ga）. Zircons from the orthogneiss （miuYC; intrusive into msuYC） show a crystallization age of 261.3 - 2.7 Ma （Capitanian; late middle Permian） which is broadly coeval with deformation, and Neoarchean-Paleoproterozoic inheritance. Meaningful core-rim relationship between Neoarchean zircon cores and late Permian rims is well defined, indicating the occurrence of Archean crust in this sector of Patagonia. Hf TDM of Permian zircons is mainly Meso-Paleoarchean （2.97-3.35 Ga）, with highly negative e（Hf） values （ca, -33）. Hf TDM of inherited Neoarchean zircon cores is also Meso-Paleoarchean （3.14-3.45 Ga） but more juvenile （ε（Hf） = -0.3）. Hf isotopes reinforce the presence of unexposed ancient crust in this area. Combining geological and isotope data, as well as geophysical models, we identify the Yaminué Complex within the La Esperanza-Yaminué crustal block flanked by two other, distinct crustal blocks： the Eastern block which forms part of the Patagonia terrane sensu stricto, located in the eastern Patagonian region, and the Western block forming part of the Southern Patagonia terrane. Their origins and timing of amalgamation to form the Patagonia composite terrane are also discussed.

Middle Permian Seamount from Xiahe Area, Gansu Province, Northwest China: Zircon U-Pb Age, Biostratigraphy and Tectonic Implications

The well-preserved seamount buildups are documented from the northwestern Qinling （秦岭） orogenic belts, Northwest China. The study sections are located in the Ganjia （甘加） area of the Xiahe （夏河） County, Gansu （甘肃） Province. The dark basalt and overlying massive reef carbonate characterize the Xiahe seamount buildup. Basalts are dominated by the olivine type of rocks and bear distinct porphyritic textures, and fumarole and amygdaloidal structures. The basalts are dominated by SiO2 （up to 48.49 wt.%-52.29 wt.%） followed by （Na2O＋ K2O） （3.80 wt.%-4.96 wt.%） and TiO2 （2.04 wt.%-2.52 wt.%）. They are featured by considerably high content of Ti. The tholeiiteseries rocks dominate the basalts, while calc-alkali-series rocks are also present. The REE of the basalts shows the LREE-enrichment type with distinct positive Eu abnormal. The trace elements of the basalts are characterized by the lack of P and high content of Ti. These geochemical signals suggest that the Xiahe basalts were formed in an ocean-island setting. The LA ICP-MS zircon U-Pb age of the basalts is 267.6±5 Ma, which is reinforced by the presnce of the fusulinid Neoschwagerina Zone of the Wordian （Middle Permian） in the limestone interbeds of the basalts. Integration of petrological and geochemical studies of seamount basalts and lateral correlation of seamount buildups reveals that the Qinling-Qilian-Kunlun orogenic belts were probably the archipelagic oceans during the Permian.