Radiogenesis of Low Maturity Natural Gas in the Turpan-Hami Basin,NW China

The origin of the Jurassic low maturity natural gas in the Turpan-Hami Basin has attracted scientists’attention for some time,and it is known that radiogenesis may have played a role.However,little has been done on the uranium-rich background of the whole basin.Based on plentiful logging and geological data for the Jurassic strata in the Turpan-Hami Basin,this research examined the features and factors controlling the distribution of rocks with high gamma reading.The results show that 70%-100%of the rocks with high gamma readings correspond to mudstones in the prodelta subfacies rather than those in semideep-deep lacustrine subfacies rich in mudstones.Therefore,we propose that the distribution of rocks with high gamma readings is mainly controlled by sedimentary facies rather than by lithology.Further analysis of the gamma spectrometry logging data shows that high gamma values are more strongly correlated with U content than with Th or K content.By comparing the U and Th contents of felsic rocks in peripheral provenances,we find that the Jueluotage Mountain and Harlik Mountain were the dominant uranium sources for the Jurassic Turpan-Hami Basin.Radiolysis due to high-level uranium in the prodelta subfacies can make the low maturity source rocks generate H2 and CH4,thus contributing to the production of low maturity natural gas in the Turpan-Hami Basin.

A review on the definitions of terms of sedimentary facies

In recent years,in some papers and manuscripts published in and submitted to the Journal of Palaeogeography(Chinese Edition and English Edition),the authors named the rocks or rock types as"microfacies"or"lithofacies",named the microfeatures in thin-sections under microscope as"microfacies",and named the macrofeatures of rocks as"macrofacies".I wrote two short papers"Words of the Editor-in-Chief—Rocks are not microfacies"(Feng,Journal of Palaeogeography 19(5):II 2017)and"Words of the Editor-in-Chief—Rocks are not lithofacies"(Feng,Journal of Palaeogeography 20(3):452–452,2018)which were in Chinese and published in the Journal of Palaeogeography(Chinese Edition).However,they did not attract much attention of readers in China and outside China.In addition,in1980 s,some Chinese sedimentologists proposed"subfacies"and"microfacies"based on the macrofeatures of rocks from outcrops and drilling cores.However,the definition of this"microfacies"is totally different from the"microfacies"proposed by foreign sedimentologists in 1940 s based on the microfeatures in thin-sections under microscope.These problems appeared repeatedly and forced me,as the Editor-in-Chief of the Journal of Palaeogeography(Chinese Edition and English Edition),to observe the policy of"A hundred flowers blossom and a hundred schools of thought contend",to write new papers"A review on the definitions of terms of sedimentary facies"both in Chinese and in English,to clarify the definitions of the terms of sedimentary facies,i.e.,"facies","lithofacies",two"microfacies","macrofacies","subfacies",etc.I hope that the new papers will attract attention of readers worldwide and they can write papers and participate in the discussion and contending of these problems,strive for getting some common understandings,and therefore promote the progress and development of sedimentology and palaeogeography.

Reservoir identification of marine facies carbonate shoals in the Middle Permian in the Sichuan Basin

Controlled by the base level change cycle,the carbonates exposed from the periodically shallowed water body at the top of the high-frequency sequence develops multiple sets of thin reservoirs.Such reservoir identification has always been tricky in the prediction of carbonate reservoirs.Based on the Middle Permian strata from the Sichuan Basin,this paper established a forecasting approach of high-frequency-sequence-controlled carbonate thin reservoir.The steps are as follows:(1)Combine the measured results of samples from the typical outcrops with changes of carbon and oxygen isotopes,thus to construct a division program for the 3rd-order sequence of the Middle Permian strata.(2)Compare the carbon and oxygen isotope changes and the global sea level change trend,determine the controlling factors of the 3rd-order sequences.(3)Carry out spectrum analysis based on the natural gamma energy spectrum logging(ln(Th/K))curves of Wells Long-17 and Anping-1 to establish a high-frequency sequence framework division program,and then apply the logging curve characteristics to correct the top interface positions of the high-frequency sequences,which is the potential location of carbonate reservoir.The research results suggest that the Middle Permian in the Sichuan Basin can be divided into three 3rd-order sequences,which are PSQ1,PSQ2 and PSQ3 from bottom to top.Among which,PSQ1 is mainly affected by global sea level(GSL)changes,and the changes originated from its tuning curve can be directly applied to the division of high-frequency sequences and reservoir prediction.PSQ2 and PSQ3 are jointly controlled by global sea level changes and regional tectonics.In cope with the influence of regional tectonics,the positions of the four-level sequence interface established according to the tuning curve need to be fully considered,and good results were achieved through systematical correction.This method can effectively reduce the risk of reservoir prediction caused by marine carbonate heterogeneity,and provide scientific foundation for the prediction of high-frequency cyclic reservoirs of platform facies and platform margin subfacies in other marine carbonate sedimentary basins.