| Based on the comprehensive analysis of a great number of exploration and development data, it is shown that the Cambrian-Ordovician limestone-predominated carbonate hydrocarbon reservoirs in Tarim Basin are quite multifarious and complicated and they are different from the typical Meso-Cenozoic carbonate reservoirs in the world. The Lower Paleozoic carbonate hydrocarbon reservoirs present four particular features in geological conditions in this basin: 1) Multi-period tectonic movements in the small craton have brought about intensive structural reformations on hydrocarbon accumulation. 2) Contributing to the late Hercynian hydrocarbon charge and the late Himalayan gas enrichment, the basin is rich in both oil and gas resources on the basis of ancient Cambrian-Ordovician source rocks. 3) Most of limestone-predominated reservoirs with reformed secondary pores are of low matrix porosity and permeability and excessive heterogeneity. 4) Carbonate reservoirs are deep buried more than 5000m with poor reservoir-cap assemblages in the basin. The Lower Paleozoic reformed marine carbonate reservoirs in the basin are characterized in four aspects: 1) The non-structural hydrocarbon reservoirs are dominant. 2) Due to multi-period charges and adjustments of the hydrocarbon reservoirs, the fluids inside are complicated and varied in property. 3) The small-scale oil and gas pools that distributed in large area with low and medium size reserve abundance are superposed and/or continued one after another. 4) Outputs of fluids(oil, gas and water) are intricate and the oil/gas production is commonly sustained by a small number of high-yielded wells. |
