鄂北杭锦旗探区上古生界天然气成藏类型

Accumulation types of Neopaleozoic gas in Hangjinqi block of north Ordos Basin

通过对杭锦旗探区泊尔江海子断裂南北两侧气水分布与典型气藏(井)解剖,发现杭锦旗探区上古生界断裂两侧气水分布明显不同,断裂以北,天然气主要聚集于构造高点,地层水分布于构造下倾部位;断裂以南,气水层分布复杂,具有致密砂岩底部含气特点,局部低幅度构造具有正常的上气下水分布特征.断裂两侧上古生界烃源岩、储集层、源储关系、气水分布及产能等成藏条件与特征具有明显的区别,其中断裂南侧成藏特征与国外发育根缘气的盆地(地区)具有很好地相似性.根据致密砂岩底部含气特征指出,杭锦旗探区上古生界太原组、山西组及盒1段等层系发育根缘气,其主要分布于伊8-锦8-伊22-锦10-锦6-伊19井一线以南地区,具体层系略有区别,该线以北为气水过渡带,气藏类型过渡为常规气藏.研究结果表明,杭锦旗探区上古生界断裂北侧应以寻找常规气藏为主,断裂以南则以寻找根缘气藏为主.

In Hangjinqi block of north Ordos Basin,the Neopaleozoic water and gas distribution is very complex,and there is great divergence in gas accumulation types.By analyzing the characteristics of the water-gas distribution and the typical reservoirs in the south side and the north side of Boerjianghaizi fault in the block,it is held that there is obvious difference in the gas-water distribution in two sides of the fault:in the north side,natural gas accumulates mainly at high part of structures and formation water distributes in the downdip parts of structures;in the south side,natural gas accumulates at the bottom of tight sandstone and there is conventional distribution of gas and formation water,that is,gas is at top and water is at bottom in partial low-amplitude structures.It is also found that in two sides of the fault,there are obvious difference in hydrocarbon source rock,reservoir,source-reservoir relationship,gas-water distribution and productivity.The accumulation characteristics of the natural gas reservoir in the south side of the fault are similar to the foreign basins(districts)developing source-contacting gas.Combining above research,it is pointed out that source-contacting gas developes in C3t,P1s and H1 of Neopaleozoic formation in Hangjinqi block according to the feature of the gas accumulated at the bottom of tight sandstone,and it distributes mainly in the south side of Y8-J8-Y22-J10-J6-Y19 well line.In the north side of the line is gas-water transitional belt,and gas reservoir type transits to conventional gas reservoir.The study results indicate that exploration targets should be conventional gas reservoirs in the north of the fault while exploration targets should be source-contacting gas reservoirs in the south of the fault in Hangjinqi block.