Key Parameters Research In Chang 7 Continental Shale Gas Evaluation, Yanchang Formation, The Central And Southern Ordos Basin

Continental shale has different particular characteristics from marine shale in sedimentary environment, sedimentary source, mineral composition, organic matter type and degree of thermal evolution, the particular characteristics were shown in rapid lithofacies change, silty mudstone developed and high residual oil saturation, so there is an important significance in the research of resources evaluation parameters. The Chang7 continental shale of Yanchang formation in upper Triassic, Ganquan-Fuxian area in Ordos Basin was selected as the research object in this paper. Based on the standardization of logging data, the strata structure framework of Chang7 formation was confirmed by stratigraphic division and correlation,. Taking advantage of the core description and test data analysis of key wells and exploring the logging response of continental shale gas lithology, organic carbon content, gas-bearing property and brittleness, the key parameters logging interpretation model of Chang7 continental shale gas in this region was built by optimization method on the basis of theoretical research. According to the longitudinal and horizontal distribution of key parameters from the model, the favorable target area of Shale gas enrichment was predicted. This study provide an important theoretical basis for continental shale gas evaluation and further exploration of Ganquan-Fuxian area.Studies suggest that:(1) The 3D crossplot method for complex lithology identification in Chang7 formation was better than 2D crossplot method. The shale thickness was variable from 3.7 to 110.9 m and the thickest area was nearby the FY2 and YY34 well. (2) The mineral composition of Chang7 shale was clay mineral, feldspar, quartz, carbonate minerals and pyrite successively. Organic carbon content was between 2.0% and 8.0%. (3) The mechanical performance of Chang7 shale was a "short elastic-plasticity" feature and the shale experienced force developed multiple horizontal split. Brittle shale in Xiasiwan-Qiaozhen area was more development, and accounted for about 60% of the total thickness of shale. (4) Desorbed gas contents in Chang7 shale was variable from 0.16 to 0.72cm3/g, residual gas contents was variable from 0.16 to 0.72cm3/g and adsorption gas contents was variable from 1.2 to 2.0cm3/g. The shale adsorption gas contents was higher in Southern Xiasiwan-Qiaozhen area. The free gas saturation was higher in southwest of Xiasiwan-Qiaozhen and Baguasi-Wangzhuangtai area. (5) According to the longitudinal and horizontal distribution of key parameters, the Southern Qiaozhen and Baguasi-heshangyuan area was predicted to the enrichment area of Chang7 Shale gas.Several key parameters evaluation method were formed in this study:(1) Sensitive logging multiple stepwise regression methods were established to interpreted total organic carbon content in shale and siltymudstone. (2) The logging interpretation model of adsorption gas under the isothermal adsorption test condition was established based on grey correlation analysis results, and corrected to the formation temperature and pressure conditions using the adsorption potential theory. (3) Selected Simandoux equation to calculate the water saturation and combined the residual oil saturation get from the porosity changes before and after washing oil, the saturation of free gas was obtained accurate. (4) Based on the analysis of mechanical parameters characteristics, stress-strain characteristics, rock rupture mode and brittleness of shale, the relationship between shear slowness, compressional slowness and density fitted by different lithologies and the shear wave velocity model was built. Calculated the dynamic mechanical parameters, the shale brittleness evaluation method was formed after calibrated by the relationship between dynamic and static mechanical parameters. (5)Through the relationship analysis between mineral compositions and rock physical paraments and petrophysical simulation, it was cleared that quartz and pyrite were brittleness minerals in shale. The mineral brittle evaluation method was proposed utilizing weighted sum the mineral volume content and brittleness coefficient of each mineral.