The Recovery Of Paleogeomorphology And Its Influence On The Sedimentary Facies In Ordovician In Tazhong Area

Tazhong uplift is one of the oil exploring area of Tarim basin. It is a secondary structure unit of Tarim central uplift belt. Its geomorphology is affected by multiple tectonic movements. Paleogeomorphology formed in different phases had different influence on the types and the distribution of the sedimentary facies in later stage, as it controls reservoir-caprocks of the oil pool in great degree.In this thesis, with the well and seismic material, we analyse the feature of the formation and the distribution of the three unconformities (T₇⁴,T₇², T₇⁰) which developed in Ordovician in Tazhong area. And the result was used to analyse the character of the denuded paleogeomorphology and the tectonic paleogeomorphology. We did research on the way the denuded paleogeomorphology affecting the karst-fracture reservoir and the tectonic paleogeomorphology controlling the reef-banks. Moreover we predicted the favorable zone the two kind of the paleogeomorphology.According to the degree of the denudation and the distribution feature of the three unconformities, there are 3 unconformities formed in this area. The T₇⁴ and T₇⁰ are regional unconformities. However, the T₇² surface is a local unconformity. The analysis of the unconformities features is the foundation of the recovery of paleogeomorphology.By the geologic extrapolation methods, we estimated the denuded value of the T₇⁴,T₇⁰ unconformities. According to these values the karstification affected by paleogeomorphology, we divided them into three units: karst-highland, karst-slope and karst-bottomland. The karst-slope is the best zone of the karst reservoir. The karst-highland and the side of the karst-bottomland nearing the slope is in the next place. Integrating the facture developed in this area, we predicted the favorable zone of karst-fracture reservoir affected by denudated paleogeomorphology.In the thesis, the tectonic peleogeophology is the terrain which formed at the time Tazhong uplift was drowned. We used a new method which was more improved than the former methods. The key of the new method is: â‘ Choose the deposit surface when the uplift was buried. â‘¡Estimate the paleobathymetry by the reflection structure and the sedimentary facies analysis. We divided the tectonic paleogeomorphology into six units: fault-highland, fault-platform, platform edgeslope, shelf slope and shallow low-platform, shelf basin, deep see basin. These units have different influence on the sedimentary facies. According to the recovered paleogeomorphology, we analysed the effect on the sedimentary facies and reef-bank reservoir and considerd that the fault-platform and its edge was the major zone where the reef-bank develops. We predicted the favorable zone of the reef-bank by the similarity of the paleogeophology.