The Comprehensive Evaluation Of CBM “Sweet Zone” In Qinshui Basin

CBM, in the occurrence shape of absorbed gas, belongs to the typical unconventional oil and gas with high industrial value. As a result, CBM sweet zone forecast is of great significance to future energy industry such as oil and gas and minerals. Previously, in general CBM sweet zone forecast, researchers made evaluations mainly from the structural evolution of coal bed, mineral composition in core coal rock, thermal evolution degree, burial depth of coal-bed, unit gas content of coal, geological conditions and resources, among others, centering on geological analysis. This thesis, in the context of the emerging approach that makes prediction about CBM gas content and coal-bed depth as well as thickness by earthquake, conducts studies on the structure and fault, collapse column, burial depth and thickness and gas-bearing capacity by various seismic attribute methods. Meanwhile, the author makes comprehensive analysis and discussion on the interpretation of different methods, and predicts the location of CBM sweet zone in the southeastern Qinshui Basin based on overall consideration of coal-bed tentonic feature, coal petrography lithology, CBM recourse characteristic and exploration capacity.Firstly, on the basis of existing achievements in geological structure analysis of Qinshui Basin, this dissertation focuses on studies on the tectonic evolution, features of geological structure, stratigraphy and coal petrography in southeastern Qinshui Basin. Faults and collapse columns are confirmed to be distributed in the area, predominately including strike-slip faults from north to south with a few ones along north-south direction, and the strip-shaped and uneven collapse columns along the north-east direction. What's more, the thesis confirms the area possesses prerequisite conditions due to proper depth of coal bed and thermal evolution degree, good coal quality and thickness, high gas content, cleat development and large amount of gas output, which lays solid foundation for predicting the sweet zone.Secondly, the dissertation applies coherence attribute and curvature attribute in attempts to make sure of the fault structure and collapse column features precisely. The author introduces the theory of the two approaches respectively and makes analysis of the advantages and disadvantages of the results under coherence method through the combination of different time aperture and space aperture with C1, C2, C3 calculating methods. It turns out that the result 50 ms, 9 point from C3 is the coherence attribute result in southeastern Qinshui Basin. The result by curvature attribute is also obtained through the research on its theory as well as the relations between curvature and geological attitude. Based on comprehensive analysis and comparison of the two attributes, the structural features of the No.3 and No.15 well coal-bed fault and collapse column are ascertained, along with the trend and location of the fault and the spatial distribution of the collapse columns, which points the way to CBM sweet zone prediction.Thirdly, targeting at making precise prediction of coal bed thickness, the dissertation introduces Sparse-spike Inversion and makes analysis of the theory, processing steps and procedures of the conversion such as well curve management, wavelet extraction and the establish of wave impedance model. Sparse-spike Inversion is conducted on 24 wells and five well ties with the result of No.3 coal bed obtained by additional studies on drilling petrography character and distribution. By comparative analysis of the actual and forecasted thickness of the No.3 coal bed, it turns out the absolute error is lower than 0.4m, thus proving the Sparse-spike Inversion to be accurate and feasible.At last, The thesis predicts coal-bed thickness by RMS amplitude and further the CBM sweet zone in the southeastern Qinshui Basin. The No.3 coal bed is predicted to have more gas in the west that the eastern and middle part. CBM is rich in strong amplitude or thick coal-bed areas, highest in the northwest and relatively high in the south. Based on discussion and analysis, the thesis indicates that the amplitude tallies with the gas bearing capacity of the wells in the southeastern Qinshui Basin, conforming to the technological standard.