川东北超致密砂岩气田储层物性下限确定方法

A Method to Determine the Lower Limit of Physical Property in Extra Low-porosity and Low-permeability Sandstone Reservoirs,Northeastern Sichuan Basin

储层物性下限一般为孔隙度下限,它直接关系到油田勘探、开发抉择。用生产法统计试气层段112个样品孔隙度都在2.5%以上,裂缝发育能进一步降低储层物性下限,同时也说明压裂等储层改造措施能有效地改造储层、提高产量。经验统计法以孔隙分布频率累计概率为20%所对应的孔隙度为储层物性下限值。最小流动半径法则利用毛管压力曲线反映储层微观孔隙结构,分析岩石微观孔喉结构,确定油气的最小流动孔喉半径;用统计分析方法建立孔喉半径与常规物性分析孔隙度和渗透率的关系,进一步求出储层的物性下限。以3种储层物性下限确定方法计算川东北致密砂岩储层的孔隙度下限为2.5%。

The so-called lower limit of physical property of reservoir always means the lower limit of porosity, which is highly related to selecting a scheme of exploration and development. After statistical accounting by production method for 112 samples from a gas-testing interval, it is demonstrated that(1)their porosities are all larger than 2.5 %(;2)fracture growth can further reduce the lower limit; and(3)some reservoir reconstruction measures, such as fracturing, can effectively reform reservoir and increase production. There are three methods to determine this limit. Firstly, by empirical statistical method, the porosity, corresponding to 20 % of porosity distribution frequency cumulative probability, is just the limit. And then, the minimum flow radius method by mercury pressure curve can reflect microscopic porous structure; and adopting this radius method can determine the minimum flow radius of pore and throat. At last, the relationship between pore-throat radius and porosity-permeability can also be established by statistical analysis; after that, the limit can be obtained. Through these methods, the porosities of tight sandstone reservoir in northeastern Sichuan Basin are calculated. And all calculated lower limits are 2.5 %.