| The Ordovician strata of lungu7wellblock has been experienced multiphase tectonic movements and long time continuous exposure, the weathering crust karstification are well-developed. The exploration situation of the work area also suggests that high oil and gas wells is closely related to the ancient karstification. This paper, by using core, imaging logging, conventional logging, drilling and logging, and seismic data, combined with the karstology, logging geology, karst geomorphology and karst water dynamics, etc, identifies the weathering crust karst in the study area, through combining core, conventional logging, drilling, imaging logging and seismic characteristics, builds weathering crust karst marks, divide karst zone, analyse each zone’s features. Combined with the seismic research result recovers the ancient landform before the Carboniferous and divides karst geomorphic units and analyse the characteristic of the karst development under different paleo-geomorphology unit. In the aspect of lithology, paleoclimate, tectonic fracture, paleo-geomorphology and hydrodynamic conditions, etc analyse the controlling factors of karst and predict development favorable area of karst. The thesis have the following understanding:(1) According to those features about the core, logging, image logging, drilling and seismic data. Referring and citing the definition of the karst facies, according to the features in the image logging, I classify the fracture-cave system into full-filled subfacies, semi-filled subfacies and unfilled facies, after that according to the characters of the filled matter, further classify those subfacies into mud filled, breccia filled and calcite filled microfacies.(2) Divide those wells in the block into epikarst zone, vertically filtering zone and horizontal flowing zone, epikarst zone have good physical property, wells can drill aven in some place, some high-angle fracture develops well, karst-cave are also filled by collapse breccia, weathering residual and chemicals. The vertical filtering, zone are with poor physical property, the high angle fractures develops, sometimes can see the enlarged dissolution, but often filling degree is high; the horizontal flow zone are with good physical property, fracture cave system develops well in this zone, the development of large karst cave is often visible.above the caves, some fracture are developed horizontal fracture and horizontal dissolution cave appears, the filled matter in the huge cave, are also muddy and silty mudstone.(3) Combined the classic theories and area geology background, Study area is located on the different second paleo-geomorphology units, which are karst highland and karst slope, referring to the others studies, more accurately divide it into3third-level paleo-geomorphology units, which are peak cluster depression, hill depression and hill cluster keel ravine, then describe the single wells in each micro-units. Each karst zones have different characters in different paleo-geomorphology units, according to the development and filling features,analyzing the statistic chart of system type, core data,image logging data and distribution and filling degree of favorable fracture-cave,the characters of fracture-cave systems in epikarst zone are better than horizontally flowing zone, that of vertically filtering zone are worst, hill depression are better than peak cluster keel ravine, that of peak cluster depression are worst.(4) Analyze the master control factors of weathering crust karst development from4respects of lithology, paleo-climate, tectonics and paleo-geomorphology, also, paleo-hydrodynamics, finally, this dissertation integrate all the recognition,refining the weathering crust karst development mode, according to the master controlling factor of fault, geomorphology and paleocurrent predicts the distribution of karst fracture-cave in plane to provide a reference for the study of karst research and exploration deployment in this area. |
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