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

加拿大是世界上稠油储量最大的国家，稠油和焦油砂储量约为3万亿桶，其中在阿尔伯塔省和萨斯喀彻温省的厚度小于10 m的薄产层中含有大量API为15-20°的稠油。由于上覆层和下伏层的热损失很大，或者由于储层非均质性高，垂向渗透率低，水平渗透率高，因此利用热法从这种薄产层开采稠油是一项具有挑战性的任务。注溶剂为稠油薄层油藏的开发提供了新的机遇。实验证明，水-溶剂交替法比连续注溶剂法更能提高稠油采收率。这主要是由于注水和延迟溶剂突破提高了波及效率。然而，水和溶剂的低粘度仍然会导致注入剂和稠油的流动性比不理想，并且在油藏中溶剂覆盖仍然是一个问题。在本研究中，我们将探索一种新的工艺，即表面活性剂-溶剂交替泡沫工艺，以研究其改善流动性控制，减少溶剂覆盖效应，从而提高稠油采收率的潜在机制。所提出的表面活性剂-溶剂交替泡沫工艺的新颖性在于两个重要机制：(1)溶剂在重油中的溶解导致油膨胀并降低其粘度；(2)泡沫的产生在水-溶剂交替工艺的基础上进一步降低了流动性，并通过减轻储层中气体的凌驾效应，实现了更好的一致性控制。这两种基本机制有望降低剩余油饱和度。本课题将进行实验和理论研究，探讨影响表面活性剂-交替溶剂泡沫工艺回收性能的基本机理。该研究结果将为提高稠油薄层采收率提供重要的见解和实用的方法。

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.