异常低含水饱和度储层的水锁损害

Water block damage of abnormal low-water saturation reservoirs

当储层原始含水饱和度低于束缚水饱和度时，称异常低含水饱和度储层，一般意义的水锁指数就不能反映该类储层的水锁损害过程和解除水锁损害的难易程度。为此，通过异常低含水饱和度储层水锁损害机理研究，提出了这类储层存在暂时性水锁和永久性水锁观点。暂时性水锁是指油、气反排外来工作液至束缚水饱和度过程中造成的水锁，是可以解除的；永久性水锁是指油、气反排外来工作液降至束缚水饱和度后再也不能降低了，从而达不到原始含水饱和度，造成一部分水锁永远无法解除。将该研究方法运用于长庆气田上古生界致密砂岩气藏的水锁损害评价实验中，结果表明：储层渗透率越低，束缚水饱和度与原始含水饱和度差值就越大，永久性水锁损害和暂时性水锁损害就越强，解除暂时性水锁所需时间越长。

A reservoir with the abnormal low water saturation refers to a reservoir with the initial water saturation lower than the immobile water saturation.The general water block index can reflect neither the damaging process of water block on such reservoirs nor the difficulty level of eliminating the damage.Through studying the mechanism of the damage of water block on the reservoirs with the abnormal low water saturation,provisional and perpetual water blocks are proposed.Provisional water block refers to the water block that is resulted from the process of oil and gas repelling the working fluid until the immobile water saturation,which can be unlocked.Perpetual water block refers to the water block that oil and gas repel the working fluid until the immobile water saturation cannot decrease so that the initial water saturation cannot be reached,which results in that a part of the water block cannot be unlocked.Experiments are carried out on the evaluation of water block damage to the reservoirs of Neopaleozoic tight sandstone in Changqing gas fields.The results show that the lower the permeability of the reservoir,the more severe the damage caused by provisional and perpetual water block and the more time is needed to unlock the provisional water block.