Issues and Options in the Delineation of Well Capture Zones under Uncertainty
Issues and Options in the Delineation of Well Capture Zones under Uncertainty
复制标题
不确定性条件下圈定井捕获区的问题和选择
作者：
E. Frind;J. Molson
在非均质多孔介质中，井口保护区（WHPA）的不确定性划定仍然是一个挑战。对于粒状介质，一种选择是将联合收割机粒子跟踪（PT）与蒙特卡罗方法（PT-MC）结合起来，以考虑地质不确定性。然而，在这种方法下，裂缝多孔介质需要某些限制性假设。对于所有类型的介质，另一种方法是捕获概率（CP）方法，该方法基于向后模式下的标准对流弥散方程的解，利用向前和向后传输过程之间的类比。在此背景下，我们回顾了目前关于传输概念模型正确形式的争议，发现对流扩散模型，它代表了不同速度的流管之间的扩散交换，比传统的对流扩散模型更符合物理现实。对于轻度到中度非均匀材料，随机理论和模拟实验表明，该过程在场尺度上收敛为有效的平流-弥散过程，可以使用适当的宏观弥散度值用常规输运模型进行模拟。对于高度非均匀的材料，随机理论还不存在，但没有理由说这个过程不应该自然收敛。宏观分散性似乎是地层特异性的。对流弥散模型可用于非均匀颗粒介质中捕获区的划分。对于裂隙多孔系统，混合等效多孔介质和离散裂隙网络或基于CP的方法可能具有潜力。一般来说，没有MC的PT划定的捕获区总是太小，不应该作为土地使用决策的基础。
The delineation of wellhead protection areas (WHPAs) under uncertainty is still a challenge for heterogeneous porous media. For granular media, one option is to combine particle tracking (PT) with the Monte Carlo approach (PT‐MC) to account for geologic uncertainties. Fractured porous media, however, require certain restrictive assumptions under this approach. An alternative for all types of media is the capture probability (CP) approach, which is based on the solution of the standard advection‐dispersion equation in a backward mode, making use of the analogy between forward and backward transport processes. Within this context, we review the current controversy about the correct form of the conceptual model for transport, finding that the advection‐diffusion model, which represents the diffusive interchange between streamtubes with differing velocities, is more physically realistic than the conventional advection‐dispersion model. For mildly to moderately heterogeneous materials, stochastic theories and simulation experiments show that this process converges at the field scale to an effective advection‐dispersion process that can be simulated with conventional transport models using appropriate macrodispersivity values. For highly heterogeneous materials, stochastic theories do not yet exist but there is no reason why the process should not converge naturally as well. Macrodispersivities appear to be formation‐specific. The advection‐dispersion model can be used for capture zone delineation in heterogeneous granular media. For fractured porous systems, hybrid equivalent porous medium and discrete fracture network or CP‐based approaches may have potential. In general, capture zones delineated by PT without MC will always be too small and should not be used as a basis for land‐use decisions.