非常规天然气产量递减分析新方法及其应用

对以裂缝流动为主的低渗、超低渗致密气井或页岩气井,传统的递减方法,如Arps产量递减及其变形,不再适用。这些井的大多数产量数据呈现出裂缝流动为主的流态,即使生产几年后也很难达到晚期流动状态。如果没有拟径向流和边界控制流动存在的话,不论是岩石基质渗透率或泄油面积都很难确定。这表明,与裂缝贡献相比,基质贡献微不足道,且预期最终采收率(EUR)不能建立在泄油面积的传统概念基础上。介绍了一种对低渗、超低渗气井或页岩气井适用的产量递减方式,用以估算以裂缝流动为主、基质贡献可忽略井的预期最终采收率,以低渗、超低渗致密气井的例子来验证这种新的递减模型。所有显示预测了直线的趋势,其斜率和截距与裂缝流态类型有关。证实此方法能得到可靠的预期最终采收率,用来代替非常规气藏传统的递减方法,分析资源远景带的产量预测和储量估计。

Foreign New Methods for Analysis on Unconventional Gas Production Rate Decline and their Application

Such traditional decline methods as Arps production rate decline and its variations do not work for low permeability and super low permeability tight gas wells or shale gas wells where fracture flow is dominant.Most of the production data from these wells exhibit fracture-dominated flow regimes and it is hard to reach later period flow regimes even after production of a few years.Without existence of pseudo radial flow and boundary control flow,it is very hard to determine permeability and oil drainage area of rock matrix.This indicates that compared with fracture contribution,matrix contribution is negligible and the expected ultimate recovery can not be based on the traditional concept of oil drainage area.Introduced a production rate decline approach for low permeability and super low permeability gas wells or shale gas wells,it can be used to estimate ultimate recovery for wells where fracture flow is dominant and matrix contribution is negligible and taken are some low permeability and super low permeability gas wells for example to verify this new model.All these examples showed a straight line trend and its gradient and intercept are relevant to fracture flow pattern.It has been demonstrated that reliable expected ultimate recovery can be obtained by using the new method and this method can be used to replace conventional decline method for unconventional gas reservoir and analyze production forecasts and reserves estimation of resources.