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

加拿大拥有全球最大的稠油储量，约有3万亿桶重油和沥青砂，其中大量API为15-20°的重油蕴藏在艾伯塔省和萨斯喀彻温省厚度不到10米的薄油层中。由于上覆岩层和下伏岩层的大量热损失，以及纵向渗透率低、水平渗透率高的储层非均质性强，用热力方法从薄油层开采稠油是一项具有挑战性的任务。注入溶剂为这些稀薄稠油油藏的开发提供了新的机遇。室内研究证明，与连续注入溶剂相比，水交替溶剂工艺对提高稠油采收率更为有效。这主要归因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使注入剂和重油的流度比变得不理想，在油藏中超越溶剂仍然是一个问题。在这项拟议的研究中，将探索一种新的工艺，即表面活性剂-交替溶剂泡沫工艺，以考察其改善流度控制、减少溶剂覆盖效应从而提高稠油采收率的潜在机理。表面活性剂-溶剂交替泡沫工艺的创新之处在于两个重要的机理：(1)溶剂(S)在稠油中的溶解导致原油膨胀并降低其粘度；(2)泡沫的产生在水交替溶剂工艺的基础上提供了进一步的流度降低，并通过缓解油藏中的气体凌驾效应而更好地控制了油藏的顺应性。这两种基本机制有望降低剩余油饱和度。该方案将进行实验和理论研究，探索影响表面活性剂-交替溶剂泡沫工艺采收率的基本机理。这一研究结果将为提高稀薄稠油油藏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.