水溶气非常规资源及其脱溶成藏

Unconventional Dissolved Gas Resources in Water and Gas Pool Formation with Degasification

在气源和水体充足的前提下,天然气溶解于水主要受溶解度控制。天然气溶解度明显随压力增大而增大、在温度为80℃左右时取得最小值、随水的矿化度增加而轻微降低;气组分溶解度的顺序大致为:CO2>N2>C1>C2>C3>C4。估计全球水溶气资源量高达常规气资源量的百余倍,是重要的非常规天然气资源。在含油气盆地的深部以及生烃坳陷附近的异常高压带,天然气溶解度大、水溶气相对富集,有利于形成高压地热型水溶气藏。当遇到后期构造大幅抬升、深断裂输导及异常高压释放时,水溶气发生脱溶,析出游离气并形成常规气藏。这种水溶、脱溶机制有效缓解了高演化盆地烃源形成早与圈闭定型晚之间的矛盾。国内外一些超大型气田(藏)的形成被认为与水溶气脱溶成藏有关。分析油气田水中的溶解气、气藏气以及含烃流体包裹体的化学组成及碳同位素组成,有助于重建地史时期天然气的水溶、脱溶过程。

With enough gas and water, solution of gas in water is mainly controlled by the solubility of gas, which increases obviously with pressure, decreases slightly with salinity of water, and gets a minimum value at about 80℃. Usually the solubility order of gases is CO2〉N2〉C1〉C2〉C3〉C4. It is estimated that the resources of gas dissolved in water is more than one hundred times larger than that of conventional gas around the world. So the gas dissolved in water is a kind of important unconventional gas resources. The deep structure or the area with overpressure near generation depression in a basin is a favorable place to en- rich the gas dissolved in water owing to the high pressure and temperature there. The degasification from water occurred under the condition of markedly structural uplift, water migration along fault or deformation of overpressure system. The solution-degasification mechanism is helpful for the later traps to match with the early hydrocarbon sources in high mature basins. It was believed that many large gas fields over the world were formed, to some extent, through the mechanism of gas solution in and degasifieation from water. The composition of gas and its isotope sampled from water, reservoir and hydrocarbon-bearing inclusion can be used to research the solution and degasification process during geological time.