致密砂岩气井产量递减组合模型的建立及应用

苏里格气田二叠系河流相砂岩气藏储集层致密,有效砂体多呈孤立状或条带状分布。气井投产后,储集层内流体长期处于不稳定流动状态,进入边界控制流时间晚,传统Arps递减方法适应性差,难以满足现场应用要求。通过分析Arps递减方法适应性差的原因,应用数值模拟方法研究了致密气藏气井递减指数变化规律,明确了递减指数与气井流体流动阶段的关系,提出在气井不稳定流动阶段采用河道线性流模型预测,进入边界控制流阶段采用Arps模型预测。气井处于不稳定流动阶段时,进入边界控制流的临界点时间由理论公式确定;已进入边界控制流阶段时,以偏离线性流的拐点为临界点时间。实例应用效果表明,采用递减组合模型预测气井递减特征及指标准确有效。

Establishment and Application of a Combined Production Decline Prediction Model for Tight Sandstone Gas Well

The Permian fluvial sandstone gas reservoirs in the Sulige gas field are tight and contain effective sand bodies that are mostly isolated or banded. After gas wells are put into production, reservoir fluid stays consistently in an unsteady flow state, and it is late to reach the boundary-dominated flow state. In this case, the traditional Arps production decline analysis method is not sufficient for field application. This paper analyzed the causes for the poor adaptability of the Arps production decline analysis method. On this basis, the variation law of the decline exponent of wells in tight gas reservoirs was identified by numerical simulation, and the relationship between the decline exponent and the flow period of fluid in gas wells was clarified. Finally, it was proposed to use the channel linear flow model to predict the production in the unsteady flow period and the Arps model to predict the production in the boundary-dominated flow period. For the gas wells in the unsteady flow period, the critical point time to attain boundary-dominated flow is determined by the theoretical formula; in the boundary-dominated flow period, the time of inflection point deviating from the linear flow is the critical point time. The field application shows that the proposed combined production decline model is accurate and effective in predicting the decline characteristics and indicators of gas wells.