Logging Evaluation Of Potassium-bearing Strata In The Sichuan Basin And Analysis Of The Geological Conditions Of The Potassium In The Favorable Area

As an important strategic resource,potassium is quite scarce in China.China's import of sylvine in 2012 ranked second in the world after India.As a result,we should draw more attention to discovery of our own potash resources and gradually strengthen the ability of self-sufficiency.Evaporite developed well in the strata of lower-middle Trias in Sichuan Basin.And rich oil and gas exploration data lays a favorable foundation for potash exploration.This paper is theoretically based on logging geology,sedimentology and geochemistry.Using methods and principles of logging interpretation,comprehensive logging response characteristics of various types of rock which are related to sylvine have been analyzed,coming to kinds of evaluation methods for polyhite and potassium-rich brine.Through the review of geological logging data,core data and logging data coming from oil and gas exploration,the paper carried out elaborate stratigraphic corrections,cross-sectional comparisons of halite rock and isopach maps of halite rock and analyzed the geological conditions for depositing sylvine in Nanchong Depression of central Sichuan and in the high and steep fold belts of eastern Sichuan.It studied comprehensive logging response characteristics of halite rock,polyhalite,green beans rock and potassium-rich brine which are all related to sylvine.Comprehensive utilization of logging data,overlapping method and cross-plot method can relatively accurately identify polyhalite stratum.With water analysis data and logging data,the logging response characteristics of potassium-rich brine have been analyzed.And based on using cross-plot method,porosity overlapping method and water saturation method to identify brine,it discussed two methods respectively through using water analysis and using conventional logging data to calculate potassium ion content.As a result,it found that using spectral logging data in conjunction with conventional logging data to calculate potassium ion content can give a more accurate result and such method applies well in the study area.Through comparing the lower-middle Triassic strata in Nanchong Salt Basin of central Sichuan in terms of lithology combination,logging response characteristics,cycle characteristics and stratigraphic thickness,as well as respectively analyzing the geological conditions for depositing sylvine of three different halite-formed periods,it comes to a conclusion that Guang'an Area is the sedimentary center of halite and polyhalite.It's the first time discovering polyhalite in T2l3-2 from the Guang'an Structure in Nanchong Salt Basin through review of old wells,single well analysis and interpretation,indicating that K+ and Mg2+ ions were relatively enriched in the original depositional brine.Through review of lots of old wells,the paper carried out several stratigraphic correlation charts,halite cross-sections and halite isopach maps of those structures in the high and steep areas of eastern Sichuan,so as to analyze the conditions for forming halite in eastern Sichuan.It found that halite developed best during the T1j4 period,and Dianjiang Area,Wanxian Area,Zhongxian Area and Dazhu Area were the main sedimentary centers.Halite developed gradually in above centers during the T1j5 period,but the scales were all smaller than that of the T1j4 period.During the T2l1 period,the development of halite stopped in the Dazhu and Dianjiang centers while continued in the Wanxian and Zhongxian centers.In terms of stratigraphic characteristics,chemistry characteristics and water types,also concerning depositional environment,it analyzed the water coming from strata of eastern Sichuan to find that the brine in study area was depositional brine and it did not meet the requirement of depositing sylvine.