多参数下低渗—致密砂岩储层含气饱和度定量预测

Multiple parameters to quantitatively predict the gas saturation in tight gas reservoirs

为了解决现阶段对低渗—致密砂岩气藏含气饱和度难以进行定量预测的石油行业难题,从经典毛细管压力公式出发,结合岩石孔隙物理模型推导出岩石毛细管力与孔隙度的平方呈反比关系,并通过模型回归优化形成纯气区所需圈闭高度与不同有效孔隙度的关系;通过引入岩石有效孔隙度和总孔隙的比值确定不同物性条件下可达到的含气饱和度上限;综合地震含气性定性平面预测成果和构造相对位置,通过条件判别和计算实现低渗—致密气藏含气饱和度的定量预测。该方法:①实现了对低渗—致密储层含气饱和度分布的定量有效预测,②能够识别生产纯气区平面分布范围及压裂大量出水的高风险区;③指导开发井水平段的部署并规避高风险区,进而降低开发风险;④更准确地判定气藏可采储量,进而为海上开发平台规模建设和低渗—致密气藏的开发等决策提供科学的依据。

As an important factor,the gas saturation in oil and gas reservoirs may affect the design of horizontal well trajectory and fracturing programming,the post-frac deliverability and water cut,and the fracturing effect.Especially for tight gas resources,both the increasing development and the application of fracturing stimulation put forward higher requirements in this saturation prediction.However,at present,it’s a difficult problem to quantitatively predict the gas saturation in tight gas reservoirs.So,based on the empirical capillary-pressure equation and combined with a physical model of rock pore,an inverse relation between capillary pressure and porosity was deduced.And another relation of porosity to trap height was formed by model regression.Moreover,the upper limit of gas saturation at different petrophysical conditions was defined based on the ratio of effective porosity to total porosity.Finally,via calculation,the gas saturation was quantitatively predicted using seismic-based gas detection and structural location.Results show that,this methodology may(1)realize the quantitative prediction on the gas saturation in tight gas reservoirs,(2)identify the planar distribution of pure gas reservoirs and an high risk area with the highest water cut during fracturing,(3)guide the horizontal well deployment to reduce development risks,and(4)accurately estimate the recoverable gas reserves,which provides science evidence for the offshore platform construction and the development of tight gas reservoirs.