Abstract:

Practice of hydrocarbon exploration in recent years indicates that Tarim Basin has following geological conditions for formating huge oil-gas fields:1. The dovelopment of large hydrocarbon-generating depressions, especially the Manjiaer Cambrian-Ordoviciandepression with a total area of 80000km², source rocks of 2000m thick and total hydrocarbon resources of 6000 million ton. 2. Uplifts of long-period developmen between the large hydrocarbon-generating depressions, especially the Shayar and Central Uplifts, which were the direction of hydrocarbon migration, and were favourable for hydrocarbon accumulation. 3. Low geothermal gradient, the mean geothermal gradient of Mesozoic and Cenozoic was about 2℃/100m, and that of Paleozoic was 2.6-2.7℃/100m. This was fairly favourable to hydrocarbon generation in late stage for major source rocks (Cambrian to Ordovician) in the basin, and slowed down the diagenetic evolution of Silurian to Tertiary clastic rocks, Therefore, the development zone of secondary pores is not only wide in longitudinal distribution (generally greater than 2000m) , but also very deep (for example, the porosity of the clastic rocks which is buried in the depth of 4300-5800m is still up to 15-25%). 4. Good preservation conditions in the later stage due to weaktectonic movements in the Meso-Cenozoic, and the development of regional cap beds which are characterized by extensive distribution, large thickness and good sealing property. 5. Well developed faults and unconformity surfaces as the main passage ways for hydrocarbon migration and accumulation, and which obviously improved reservoir property of Lower Paleozoic carbonate rocks, especially the unconformity surfaces of the PreMesozoic that usually formed weathering surface reservoirs.