南海天然气水合物水平井降压开采诱发沉积物力学响应规律

Mechanical response of sediments induced by horizontal well depressurization of natural gas hydrate in South China Sea

针对南海泥质粉砂型天然气水合物沉积物的物性和力学性质,建立水平井降压开采过程中井周沉积物的流-固-热-化响应模型,采用弹塑性模型表征塑性变形规律。结果表明:重力作用导致深层水平井压降程度低于浅层水平井,一定程度上抑制水合物分解前缘的扩展,导致深层水平井产能略低于浅层水平井;在降压开采初期水合物分解前缘未形成时,沉积物层塑性应变不明显;随着降压开采时间的增加,水合物分解区力学性质劣化显著,分解区的内聚力等强度参数变低;分解区的塑性应变明显高于未分解区。

Based on the physical and mechanical properties of the shaly silt sediments in South China Sea,a thermal-hydraulic-mechanical-chemical response model simulating the horizontal well depressurization was established.The elastic-plastic model was used to characterize the plastic deformation.The results show that the pressure drop of deep horizontal well is lower than that of shallow horizontal well due to gravity effect,which restrains the expansion of hydrate dissociation front to some extent and leads to the productivity of deep horizontal well lower than that of shallow horizontal well.When the front edge of hydrate dissociation is not formed at the beginning of depressurization mining,the plastic strain of sediment layer is not strong.With the increase of depressurization mining time,the mechanical properties of the hydrate decomposition zone deteriorate significantly,and the strength parameters such as cohesion in the decomposition zone become lower.Plastic strain in dissociated zones is obviously higher than that in undissociated zones.