Research On Gas-bearing Systems In Sequence Frame

At present,it still needs to be systematic researched on key stratum of unconventional gas-bearing system in coal measures.In this paper,we took the Late the natural gamma data sequences based on sedimentology,sequence stratigraphy,geophysical logging and related mathematical theories.The paper proposed logging sequence analysis method,established high-resolution identification of key stratum based on sequence-deposition-well logging,systematically described the key stratum characteristics and defined them,and discussed the control mechanism of sequence stratigraphy to gas-bearing systems.Subsequently,the space-time configuration mode of the gas-containing system was established.The main research contents and the results are as follows:?1?We proposed a new logging sequence analysis method,namely cumulative noise?CUSUM_IEEMD?.Compared with the original logging cuve?eg.natural gamma?,the periodic characteristics of the test quantity curve constructed by the proposed method are more significant,and the location of the mutation point is more obvious.On the this basis,we divided the research object into 4 second-order sequences and 13 third-order sequences,then established the logging sequence stratigraphic framework,whose sedimentary evolution had experienced the deposition process from the barrier sand dam-lagoon tidal flat,carbonate tidal flat to the shallow water delta,river phase.Futher analysis shows that the most important controlling factors of regional sequence stratigraphy are relative sea level rise and fall,and the sequence stratigraphy filling mode is the one of the continental surface gentle slope basin controlled by sea level change.?2?The parameters of coal system including the followings:vertical gas-bearing sedimentary combination,reservoir fluid pressure,groundwater closure,breakthrough pressure,pore infiltration characteristics,gas content and other parameters are analyzed.Then,according to whose vertical variation laws,the late Paleozoic coal system in the study area can be divided to five gas-bearing systems.In addition,the key strata were identified by employing the ISODATA classification method using the IEEMD-wavelet de-noising of the resistivity well logging data.The results were well corresponding to the recognized gas-bearing systems,therefore,a new method of high-resolution identification of key stratum based on sequence-deposition-well logging was established,which means that the regional water-blocking gas barrier layer needs to be a thicker argillaceous or siltstone layer with a CUSUM_IEEMD positive high value mutation point and an ISODATA classification level of D^I.Finally,we comprehensively evaluated the development and gas content of the five gas-bearing systems,and considered that the system IV and system II were better,followed by system III?system I and system V.?3?We pointed out the lower thresholds of each parameter of gas-bearing system key stratum in regional coal system,and then gave the specific definition of the key stratum of gas-bearing systems.The specific expression as the key stratum of gas-bearing systems should be the dense mudstone,silty mudstone or argillaceous siltstone which was generally developed in the whole region and had good continuous,and thickness over 5 m,permeability below 1×10^-4 mD,breakthrough pressure over15 Mpa.?4?The control mechanism of sequence stratigraphy to source rocks,reservoirs and key strata of gas-bearing systems is discussed.Specifically,the rise of the reference plane of the sequence stratigraphy is conducive to the development of source rocks and the decline of stratum datum is conducive to the development of sandstone reservoirs.Subsequently,the space-time configuration mode of the gas-containing system was established.This mode indicates the sequence stratigraphic framework limited the material and physical basis of the gas-bearing system.Meanswhile,the complete gas-bearing system should have one or more such cycle,which contains the high-level system domain,the low-level system domain and the transgressive system domain from bottom to top.