Periodic Logging Identification And Application Research Of Lacustrine Mud Shale Astrostratigraphy

The success of shale gas exploration and development in North America has set off an upsurge of unconventional oil and gas exploration and development in the world.It puts higher requirements for fine classification of shale formation.In traditional stratigraphy,fine grained sediments are usually regarded as a whole layer series,ignoring its internal cyclicity.Obviously,it can hardly satisfy the need of unconventional reservoir exploration and development.Therefore,the Milankovich theory was introduced as a basis for the stratigraphic division of shale sedimentary strata to find the rule of climate change under the control of the Milankovich cycle and to predict the favorable oil and gas reservoirs.The article is focused on the in the half-deep lake and deep lake facies of lower 3rd member of Shahejie Formation.The target strata is divided by the astronomical stratigraphy theory,the division is based on the combination of geology and logging including core observation,elemental analysis,geochemical indicators,physical property parameters and logging.The relationship are obtained among the astronomical stratigraphy,the climate change and abundance of organic matter.It's feasible to figure the favorable reservoir through the relationship and the physical properties distribution regulation controlled by astronomical circle.Firstly,the astronomical stratigraphy developing history are cleared by the investigate and survey of a large number of literature.Some easy-mixed basic conception and terms are summarized which is helpful to the base of the article and the development of the astronomical stratigraphy theory.In addition,point out the developing direction of astronomical stratigraphy,clarifying the relationship between logging information and multi-scale stratigraphic cycles and being helpful for fine classification of thick and fine shale formations.Secondly,comprehensively analyzing the monolithic climate change regulation by the core photograph,elements analysis and the kerogen evolution feature figures that the lower bed of the target stratigraphy is informed in the dry and cold climate.Thirdly,the interface,the scales and the frequency in different circle degrees are recognized by the simulative curves.The computing method includes the numerical modeling,the Fourier transform,the wavelet analysis.Fourthly,the chronostratigraphic framework of lower 3rd member of Shahejie formation in thousand years is established by the comparing of the Astronomical orbital theory curves and the resolving of the GR curve.The logging curves are resolved by the power spectrum analysis and Wavelet Transform in multi-degrees to find the ascendant circles' scale to resolve the GR logging curves.Fifthly,there is a relationship between SGR curve and the paleoclimatic change which is obtained from the uranium element and the eccentricity ratio.The inverting theory of the paleoclimate and the palaeoenvironment is established and it's figured that the higher uranium element rate means more moist and hot climate.Finally,the relationship among the paleoclimate change regulation in astronomical circle,the porosity and the TOC content which are important to oil and gas reservoir are studied by the elemental analysis.Larger eccentricity is benefit for forming favorable reservoirs.And the 10th,11th and 14th eccentricity ratio cycle has hot and moist climate,high TOC content,high brittleness modulus which is good Shale oil and gas reservoir.It provides a new method for the prediction of‘sweet spot' in thick shale strata.This method established for identifying astronomical period in thick bedded shale strata,which can do stratigraphic division of shale strata effectively,and improve the chronostratigraphic precision in mud shale strata.Meanwhile,it can also provide a new way for the fine division and correlation in unconventional shale oil and gas formation.Moreover,the relationship among the astronomical periods,climatic change and the parameters of reservoirs has an important value for the prediction and evaluation of favorable reservoirs in mud shale formation.