Recognition Of Multi-coalbed Methane Bearing System

Based on sequence stratigraphy and cyclic stratigraphy, the typical drillings inUpper Permian in western Guizhou Province were focused on to carry out thegeological study on logging data with the wavelet analysis technique. The recognizingmethod and technique of logging–sedimentary geology–sequence stratigraphy inmulti-coalbed methane bearing system in study area were found out by cluster analysison the basis of sedimentary controlling factors of coalbed methane formation andreservoir. The main research contents and the results are as follows:(1) The regional isochronism contrast effect of recognized Milankovitch cycleis obvious by doing the ideal Milankovitch cycle contrast test research, especially forthe long eccentricity cycle. The controlling effects of Milankovitch cycle have uponcoal accumulation event in Upper Permian in study area were revealed by thecorrelation of solar radiation, long eccentricity cycle and sea-level changing trend. Thelong eccentricity cycle corresponds to the sea-level change while the main coalbed wasmainly developed in the in the middle-upper part of long eccentricity cycle with thedelta migration.(2) Four third-order sequences were recognized and wavelet analysis recognizingpattern of third-order sequence was built by studying signals in different subsequencesets with the recognized Milankovitch cycle as a ruler. The whole Upper Permian weredivided into8medium term cycles and19short term cycles with the energy changingcharacteristics in wavelet spectrum while the high resolution sequence stratigraphicframework of regional loggings was set up.(3) Facies of Upper Permian in study area are a combination of delta, lagoon-tidal flat and carbonate tidal flat. The sedimentary evolvement characteristics insequence stratigraphic framework and the controlling effects which sequencestratigraphy and palaeogeographical framework have upon independent gas-bearingunit have been discussed. In coal-bearing strata of Upper Permian, the coalbed whichprovided gas and the mud rock seam which was considered a generalwater-isolation and gas-resistance layer is an important layer. By comprehensiveanalysis of coalbed and thickness of mud rock seam in short term cycles, it is foundthat the number of coalbed methane bearing units gradually decreased from lagoontidal flat to delta and carbonate tidal flat.(4) The recognizing method of multi-coalbed methane bearing system of logging –sedimentary geology–sequence stratigraphy in Upper Permian was found. The thickhigh-resistance layer and the ascending and descending transitional surface of baselevel cycle were chosen to divide the independent coalbed methane bearing units incoalbed methane bearing system. Combined with the coalbed development situation,the recognition of multi-coalbed methane bearing system was accomplished and thedividing result matches the actual height perfectly.