深盆气成藏门限及其物理模拟实验

CRITICAL CONDITION FOR GAS ACCUMULATION IN THE DEEP BASIN TRAP AND PHYSICAL MODELING

深盆气藏是特殊机理形成的一种储层致密的天然气藏。勘探实践和物理模拟实验表明 ,深盆气成藏过程中存在一个临界地质门限 ,这一门限可以用储气砂层的临界孔喉半径表达。只有在低于临界孔喉半径的致密砂层中 ,当深盆气分子膨胀力小于致密储层孔喉毛管力与上覆水静压力之和时 ,天然气才能在水封条件下形成深盆气藏。已发现的所有深盆气藏的孔隙度均小于 1 2 %和渗透率均小于 0 .987× 1 0 -3 μm2 。常温常压下的物理模拟实验证明 :单一微细玻璃管直径大于 0 .3cm时 ,水不能封气而形成“深盆气藏”;漏斗状玻璃管的水封气门限为 0 .1 0 2～ 0 .35 9cm,且随夹角增大而减小、随注气速率增加而增加 ;单一填砂粗玻璃管的封气门限取决于所装砂粒粒径的大小 ,粒径小于 0 .0 5～ 0 .1 mm的砂粒能够封气。实验条件下和实际地质条件下的门限值差异大 ,反映了温压条件和介质的润湿性等因素对深盆气成藏门限的影响 ;所以 。

Deep basin gas reservoir is a kind of gas reservoir with tight sandstone and formed in a unique mechanism Exploration practice and physical modeling results show that the formation of deep basin gas reservoir is controlled by the critical condition which can be expressed quantitatively in the size of the pore throat of the sandstone reservoir Can only the gas accumulate in the tight sandstone to form deep basin gas reservoir if its expansion pressure in the underground is larger than the sum of the capillary pressure and the water column pressure Statistical study on the discovered deep basin gas reservoirs show that the porosities and permeability for sandstone reservoirs are respectively less than 12% and 0 987×10 -3 μm 2, while physical modeling results under normal temperature and pressure show that the critical diameter for a single glass tube to accumulate 'deep basin gas' under water is less than 0 3 cm, less than 0 102~ 0 359 cm for a cone shaped glass tube, decreasing with its angular increase and increasing with the increasing of the gas pouring rate The critical condition for a larger glass tube filling with sands is controlled by the size of the sands, their critical diameters for gas accumulation under water are less than 0 05~0 1 mm The critical conditions for 'deep basin gas' to accumulate under water in physical models under normal temperature and pressure is different from that observed on the discovered 'deep basin gas reservoirs', indicating the effects of temperature, pressure, medium condition and so on in the underground, so they can not be directly applied to a sedimentary basin