低渗透稠油油藏水平井极限动用范围

低渗透稠油储层具有明显的启动压力梯度,油藏储量动用受到更多条件的限制。基于低渗稠油油藏基本渗流特征,首先通过稳定逐次逼近法分析衰竭开发不稳定渗流过程,得到考虑启动压力梯度影响的直井渗流方程基本解;在此基础上,利用保角变换方法,建立考虑启动压力梯度影响下水平井在三维空间上的压力分布和驱替压力梯度分布计算模型;根据油藏开发的要求,提出考虑启动压力梯度影响时衰竭开发方式下水平井储量极限动用范围的确定方法,包括平面上的极限动用半径和垂向上的极限动用厚度。基于实际油田参数计算和分析表明,水平井在水平平面上的极限动用半径较大,而在垂向平面上的极限动用厚度较小;只有同时考虑水平井在水平平面和垂向平面上的极限动用范围,才能合理部署水平井开发井位,提高油藏储量动用程度。

Limit drainage radius of horizontal wells in low-permeability heavy oil reservoirs

A threshold pressure gradient may exist in heavy oil reservoirs with low-permeability, and their effective oil productivity can be restricted due to complicated conditions. The unsteady flow process for natural depletion in heavy oil reservoirs with low-permeability was analyzed using a method of steady-state successive approximations. A solution for the flow equations of a vertical well was obtained considering the influence of the threshold pressure gradient. Based on the theory of conformal transformation, a 3D model was established for calculating the pressure distribution and pressure gradient distribution of a horizontal well. In accordance with the requirements of oil reservoir development, a method was proposed to determine the maximum drainage volume of a horizontal well when the influence of threshold pressure gradient was taken into account. The results of a case study show that the drainage radius in horizontal directions of a horizontal well is much larger than that in vertical directions. The limitations on the drainage radius both in horizontal and vertical directions should be considered during the oilfield exploration and development, and the position and orientation of horizontal wells need to be determined accordingly in order to achieve a high recovery factor.