Karst Palageogeomorphology And Reservoir Characteristics Of Ordovician Weathered Crust In Eastern Ordos Basin

This paper made in-depth research of the weathering crust paleogeomorphology and karst reservoir characteristics,by closely combined with the actual exploration, of ordovician weathered crust for object in eastern Ordos Basin,,with multidisciplinary geological theory and technology for guidance, made full use of drilling well logging and logging display, core observation, experimental analysis, the production test results,two-dimensional seismic data,etc, combined the geological methods with seismic methods closely. Set up the regional stratigraphic framework, summarized the stratigraphic characteristics; found out the remaining status of weathered crust strata; Implemented the current tectonic characteristics and ancient tectonic evolution characteristics of fluctuation strata of the weathered crust; analyzed stratum depositional environment conditions of the weathered crust development layer segment, summarized types of their sedimentary facies,sedimentary characteristics and rock assemblage, through fine stratigraphic division and correlation of the objective interval that located above and below erosion surface. Combined with the evolution characteristics of palaeozoic geological structure, deeply discussed methods and ideas of paleogeomorphology restoration about Ordovician weathered crust, determined the basis and the principle that distinguished palaeogeomorphology unit attribute, established comprehensive geological model and seismic interpretation model of dividing and interpretting palaeogeomorphology units; explored the new methods of paleogeomorphology restoration. Made preliminary recovery of the weathered crust palaeogeomorphology by using respectively the "Impression method" and "residual thick method" based on these, combined results of the "Stamping method"and" Residual thick method" with the geological and seismic methods,and, eventually completed recovery research of the weathered crust palaeogeomorphology by using "synthesis method". On that basis, according to core observation and well logging data, divided and discusses characteristics of hydrodynamic force and petrology zonation of weathered crust; established ancient karst development model in the basin east; made the detailed layering discussion and comprehensive assessment on the petrology characteristic, physical property characteristics, ancient karstification, and bore-hole-split system of the karst reservoir according to the palaeogeomorphology units;summarized the major controlling factors of the karst reservoir development; foretasted favorable zones of the ancient karst.The results show that the stratum sequence preservation of the Ordovician weathered crust development layer segment was quite completely in the basin east, developed the Ma6 segment limestone on it's top, and it's bottom board was Ma55 black limestone;those stratum between its belong to supratidal and intertidal subfacies sedimentation of the continental sea carbonate tableland, there are developmenal dolostone.and a better karst reservoir foundation; Ma51layer segment that is a regional main gas bearing layer had more residual thickness,and wide distribution. Paleogeomorphology of the researched area basically is located in the developmental area of the karst slope and karst basin,can be further identified and divided into 12 sort three-level paleogeomorphology units,such as monadnock,tablelands,tableland tableland margin,steps level ground,cheuch and depression,etc. Ancient karstification intense; the karst reservoir mainly belongs to double porosity media reservoir with the extra-low to ultra-low porosity and permeability, it's development degree was mainly controlled by the phase belt, lithologic character, diagenesis, paleogeomorphology and other factors. The development areas of tableland margin and steps level ground in karst slope are optimum places of the weathered crust reservoir in this area;he plane distribution of the porosity and permeability have the characteristics with "three high and "two low";synthetically determined three favorable zones of the karst reservoir development.