鄂尔多斯盆地北部塔巴庙地区上古生界低压力异常及其与产气性的关系

通过对鄂尔多斯盆地北部塔巴庙地区上古生界地层压力的分布规律、压力历史恢复及其与产气性关系的详细分析,认为上古生界气藏现今属异常低压-常压气藏,各气藏及同一气层的不同区域多为不同的压力系统,气藏横向连通范围有限,与阿尔伯达埃尔姆沃斯地区典型的的深盆气藏有较大的区别;上古生界烃源岩流体压力的演化历史恢复结果及平衡深度法计算证实上古生界泥岩在最大埋深时(早白垩世末)古压力系数达1.46~1.62;现今上古生界储层的异常低压是由历史中的古高压演化而成的,目前塔巴庙地区上古生界为一个高低压相间共存的复杂压力系统;区域压力封盖层——上石盒子组控制了上古生界天然气成藏,目前发现的天然气在纵向上集中分布于下石盒子组、山西组及太原组;上古生界气层压力与气层分布、无阻流量、物性、气藏流体特征有较密切的关系,相对高压力的盒3段、盒2段、太原组为较有利层段,92%的高产气井分布在压力系数大于0.95的区域内,地层压力较低的山1段产气性较差。研究资料显示盒3、2段有明显的富集成藏过程。盒3、2段为下生上储富集型气藏,太2段表现为自生自储近距离聚集型气藏。

THE DISTRIBUTION RELATION OF FORMATION PRESSURE AND ACCUMULATIONS OF NATURAL GAS AT TABAMIAO REGION IN NORTH ORDOS BASIN

Detailed analysis on the relationship between the distribution regularity,Upper Paleozoic strata pressure,restoration of pressure history and the gas production revealed that,at present,the gas pool is an exceptional low pressure to normal pressure one.The pressure system is different for different gas pool and for different sections in the same gas pool,and therefore,the scope of lateral connection is limited.The restoration of evolution history of the fluid pressure from the Upper Paleozoic hydrocarbon rocks and the calculation of balance depth indicated that the pressure coefficient,when the Paleozoic mudstone at maximum burial in the early Cretaceous,was 1.46~1.62.Present exceptional low pressure of the Upper Paleozoic reservoir was resulted from the evolution of historic ancient high pressure.At present the pressure system in the Upper Paleozoic of Tabamiao area was a complicated one characterized by the coexistence of intercalated high and low pressure.The Shihezi Formation was considered as the regional pressure cover hayer and controlled the accumulation of natural gas,which concentrated in the low Shihezi Formation,Shanxi Formation and Taiyuan Formation respectively.There were close relations between the pressure of gas pool and the distribution of gas,physical property,and fluid feature in gs pool.The Member He 3,Member He 2 and the Taiyuan Formation with relatively high pressure were favorable sections,for 92% of the high production gas wells occurred in the area with the pressure coefficient over 0.95,compared with the low production gas wells for San Member 1 with low stratigraphic pressure.Various data indicated that the Member He 3 and Member He 2 is of obvious accumulation process and belong to bottom formation,top accumulation gas pool.