Mechanistic Study of Surfactant-Alternating-Solvent Foam Process for Improving Heavy Oil Recovery

加拿大拥有全球最大的重油储量，重油和焦油砂储量约为3万亿桶，其中大量API为15-20°的重油蕴藏在阿尔伯塔省和萨斯喀彻温省厚度小于10 m的薄产层中。由于上覆层和下伏层的大量热损失，或者由于储层的高度非均质性（具有低的垂直渗透率和高的水平渗透率），用热方法从这样薄的产层中开采稠油是一项具有挑战性的任务。注溶剂技术为薄稠油油藏的开发提供了新的机遇。室内研究表明，水-溶剂交替工艺比连续注溶剂工艺更能有效地提高稠油采收率。这主要归因于由于注水和延迟的溶剂突破而提高的波及效率。然而，水和溶剂的低粘度仍然使得注入剂和重油的流度比不理想，并且储层中的溶剂覆盖仍然是有问题的。在这项研究中，提出了一种新的方法，即，将探索表面活性剂-交替溶剂泡沫工艺，以研究其改善流度控制、减少溶剂覆盖效应从而提高稠油采收率的潜在机理。所提出的表面活性剂-交替溶剂泡沫工艺的新奇在于两个重要的机制：（1）溶剂在重油中的溶解导致油溶胀并降低其粘度;和（2）除了水-交替溶剂工艺所提供的流动性降低之外，泡沫的产生还提供了流动性的进一步降低，以及通过减轻储层中的气体覆盖效应来更好地控制一致性。这两种基本机制预计将导致较低的残余油饱和度。本计画将进行实验与理论研究，以探讨影响表面活性剂-交替溶剂泡沫法回收效能的基本机制。研究结果将为薄稠油油藏提高采收率提供重要的理论依据和实用的方法。

Canada has the largest heavy oil reserves worldwide with around 3 trillion bbls of heavy oil and tar sands, among which a large amount of heavy oil with 15-20°API is contained in thin payzones with thickness less than 10 m in Alberta and Saskatchewan. It is a challenging task to recover heavy oil from such thin payzones with thermal methods either because of the extensive heat loss to overburden and underlying zones or due to high reservoir heterogeneity characterized with low vertical permeability but high horizontal permeability. Solvent injection provides new opportunity for developing these thin heavy-oil reservoirs. Water-alternating-solvent process is proven by laboratory study to be more effective for improving heavy oil recovery compared to continuous solvent injection. This is mainly attributed to the improved sweep efficiency due to water injection and delayed solvent breakthrough. However, the low viscosity of water and solvent still makes the mobility ratio of injectant and heavy oil undesirable, and solvent overriding in a reservoir can still be problematic. In this proposed research, a new process, i.e., the surfactant-alternating-solvent foam process, will be explored to examine its underlying mechanisms for improving mobility control, reducing solvent overriding effect, and hence enhancing heavy oil recovery. The novelty of the proposed surfactant-alternating-solvent foam process lies on two important mechanisms: (1) dissolution of solvent(s) in heavy oil leads to swelling the oil and reducing its viscosity; and (2) the foam generation offers a further mobility reduction in addition to that given by water-alternating-solvent process, as well as a better conformance control by mitigating gas overriding effect in the reservoir. These two fundamental mechanisms are expected to result in lower residual oil saturation. This proposal will conduct experimental and theoretical studies to explore the fundamental mechanisms that affect the recovery performance of surfactant-alternating-solvent foam process. The findings from this research will provide critical insights and pragmatic methods for enhancing oil recovery in thin heavy oil reservoirs.