定容凝析气藏动储量计算简易新方法

A new simple method for calculating dynamic reserves of constant volume condensate gas reservoir

Fetkovich油气两相气油比预测方程式反映出当储层反凝析油饱和度达不到流动条件时,生产气油比取决于储层凝析油的含量;而凝析气PVT等容衰竭实验也是在保持凝析油始终不排出条件下测定的。基于这两点认识,本文对衰竭式开发的定容凝析气藏提出了采用实际生产气油比拟合实验气油比曲线,确定天然气动储量的简单方法(以下称简易新方法)。为明确简易新方法的适用条件,推导出新的凝析油饱和度计算公式,并联立Walsh广义物质平衡方程式和Fetkovich油气两相气油比预测方程式,形成了考虑凝析油流动的定容凝析气藏动态预测方法。以特高凝析油含量的凝析气藏为例,采用该方法对凝析油流动性与累积气油比的关系进行敏感性分析,明确凝析油在完全可流动与完全不流动状态下,气油比预测结果差异很小,证明了简易新方法对低、中、高凝析油含量的各类凝析气藏都具有较好的适用性。简易新方法仅需PVT等容衰竭数据和产量数据,突破了现有动储量计算方法对地层压力和井底流压的依赖,且计算过程简单,结果与Walsh广义物质平衡方程式相近,具有重要的推广应用价值。

The Fetkovich equation of oil-gas two-phase gas-oil ratio prediction reflects that the production gas-oil ratio depends on the reservoir condensate content when the reservoir retrograde gas condensate does not reach the flow condition;and the condensate PVT constant volume decay experiment is also measured under the condition that the condensate is always not expelled.Based on these two understandings,this paper proposes a simple method to calculate the dynamic natural gas reserves by fitting the experimental gas-oil ratio curve with the actual production gas-oil ratio for constant volume condensate reservoirs developed in depletion development mode.In order to clarify the applicable conditions of the simple new method,a new condensate saturation calculation formula is derived,and the Walsh generalized material balance equation and Fetkovich oil-gas two-phase gas-oil ratio prediction equation are juggled to form a dynamic prediction method for constant volume condensate gas reservoir considering condensate flow.Taking condensate reservoirs with ultra-high condensate content as an example,this method is used to perform sensitivity analysis on the relationship between condensate fluidity and cumulative gas-oil ratio,and it is clear that the difference in prediction results of gas-oil ratio between fully flowable and fully immobile condensate is very small,which proves that the simple new method has good applicability to all types of condensate reservoirs with low,medium and high condensate content.The simple new method only requires the PVT data during constant volume depletion and the production data,it breaks the dependence of existing dynamic reservoir calculation method on formation pressure and bottom hole flow pressure,and the calculation process is simple and the results are similar to the Walsh generalized material balance equation.Therefore,the method has important application value and deserves to be promoted.