苏里格致密砂岩气田储层岩石孔隙结构及储集性能特征

基于覆压条件下储层渗透率的变化特征,分析认为苏里格气田整体为致密砂岩气田。在50~60 MPa的覆压下,渗透率相对变化量的1/3次方与常压渗透率的1/2次方表现为线性关系。储层孔隙度表现出一定的覆压敏感性,覆压孔隙度与常压孔隙度比值的1/3次方与常压孔隙度表现出较好的线性关系。扫描电镜及常规压汞实验分析表明,储层孔隙半径表现为百微米级至纳米级尺度的连续分布,渗透率越小的储层微米级孔隙所占比例越少,纳米级孔隙越多;储层喉道半径总体小于1 μm,表现为纳米级尺度的连续分布。束缚饱和度与渗透率具有一定的负相关性,与特定渗透率值对应的束缚饱和度并非定值,而是一个数值范围。拟合分析表明常压孔隙度与单位厚度储能系数呈较好的幂函数关系。由于物性越差的储层覆压敏感性越强,含气饱和度越低,其储气能力也越差,因此蕴含的天然气资源也越小,物性较好的储层则反之。

Characteristics of the pore structure and storage capability of Sulige tight sandstone gasfield

The Sulige gasfield is on the whole regarded as a tight sandstone field based on the permeability of reservoirs under overburden. There exists a linear relation between the permeability with a relative variation range to the 1/3 power and the normal one to the 1/2 power under 50~60 MPa. The porosity of reservoirs is sensitive to overburden stress to some extent and a fairly good linear relation is also found between the 1/3 power of the overburden porosity/normal porosity ratio and the normal porosity. Data of the SEM and mercury-injection experiment indicate that the pore radius shows a continuum distribution from the hundred-micrometer scale to the nanometer one. The lower the permeability of reservoirs, the less proportion the micron-pore has and the more pore-space the nano-pore takes. Most throat radius is less than 1 μm, representing a nanometer-scale continuum distribution. There exists a negative correlation between the irreducible water saturation and normal permeability. The irreducible water saturation corresponding to a given permeability is not a definite value but a value range. The fitted relation shows that there is a power function relation between the normal porosity and the reserve coefficient per unit thickness. Because of the higher porosity sensibility to overburden stress and the lower gas saturation, reservoirs with lower porosity contain less natural gas resources than those with higher porosity.