超稠油SAGD开采陆相含泥岩夹层油砂扩容机理及渗流评价研究

Steam Assisted Gravity Drainage (SAGD) has become the mainstream technology for ultra-heavy oil recovery in Xinjiang oilfield, the success of which depends largely on shortening of preheating period as well as forming homogeneous and highly permeable dilation zone in land-facies oil sand layer. Effort towards this end has brought about substantial challenge to engineering practice, especially when the impact of mud stringers is taken into consideration. In this regard, this research utilizes high-pressure, high temperature triaxial tests for rock, which is able to simulate temperature, confining stress and injection pressure the in-situ oil sand is under, so as to investigate mechanism and quantify magnitude of the dilation in land-facies ultra-heavy oil sand through both preheating and steam-circulation periods. The principle of microcrack propagation in oil sand is investigated, so are the stress-strain relations and the evolution of permeability of oil sand, mudstone and sand-mud interlayer matrix. In addition, scanning electron microscopy (SEM) and micrometer computer topography (CT) are used to image the microstructure of core samples before and after triaxial tests. Combining the aforementioned experimental analytical results, together with what has been done in literature on the dilation mechanism of marine-facies ultra-heavy oil sand, a universal numerical model on the dilation mechanism for ultra-heavy oil sand is established, which can provide theoretical and technical support for quantitatively evaluating the permeation effects of dilation zone over the entire SAGD recovery process.

蒸汽辅助重力泄油（SAGD）技术已成为新疆油田开采超稠油的主要方式，其成功的关键在于缩短预热周期并在陆相油砂产层中形成均匀高渗的扩容带。如何评价扩容发生的机理和程度给工程实践带来极大挑战，尤其是考虑泥岩隔夹层的影响时，该问题更加突出。针对这一技术难题，本项目利用高温高压岩石三轴实验模拟现场油砂所处温度、围压和承受的注入压，开展陆相油砂在SAGD快速预热和蒸汽循环两种阶段的扩容机理分析和扩容程度定量化评价，探寻扩容过程中油砂微裂缝的发育规律，获得油砂、泥岩和砂泥互层的应力应变关系和渗透率的演变。同时采用扫描电镜和微米CT实验方法，获取岩心在三轴实验前后的微结构变化。综合已有海相油砂相应成果并综合本项目研究结果，建立描述油砂扩容机理的通用数值模型，为实现贯穿SAGD生产周期的扩容带渗流效果的定量化评价提供理论技术支撑。

蒸汽辅助重力泄油（SAGD）技术已在新疆风城油田得到广泛应用，是开采其非固结砂岩储层中的超稠油的关键技术。由于风城超稠油油藏泥质夹层发育、渗透率低、非均质性强，导致预热周期长，从而使得能耗高、产出液处理成本大，严重制约SAGD预热及开发效果。预热前对双水平井挤液扩容储层，可有效增大井间区域的孔隙度、渗透率，快速建立两井的水力、热力连通，可大幅缩短预热周期。然而，针对此储层改造方式的效果亟需定量化的评价依据；同时针对物性非均质性强、泥质夹层发育的情况，需要给出非均质性定量评价的方案并和对应的改造措施。本项目从室内实验出发，首先定量刻画了油砂的弹塑性本构参数和渗流参数，研究了油砂剪切扩容（亦称剪胀）和张性扩容两种扩容机理。其次考虑塑性体应变和温度的作用，采用带盖帽的改进Drucker Prager本构模型描述油砂的扩容机理，提出了考虑温度并基于应变张量动态演变的渗透率张量动态模型，建立了SAGD井挤液扩容效果预测流固耦合有限元计算模型。通过该模型分析了油藏几何、储层物性、注液温度、力学及孔渗参数对挤液扩容所致储层变形及渗流的影响，发现渗透率是对扩容效果起决定作用的因素；注入液温度增加了井周油砂的塑性造成孔压较难扩散，使得扩容更集中于井周区域。基于有限元计算结果，提出了定量描述储层挤液扩容效果的水力连通系数（CP）的概念和计算方法。进一步地，提出了定量描述储层非均质性的综合非均质性系数的概念和计算方法，提出了射流联作挤酸改造泥岩夹层的施工方法。同时，设计并制作了测量高温及油藏压力下稠油流变性的装置，研究了稠油在注蒸汽预热阶段的流动状态，建立了考虑稠油相变的储层温度场预测模型。本项目的研究成果能为深入理解稠油储层改造中的地质力学行为、优化设计挤液扩容施工方案、评估后期循环预热效率提供理论与工程指导。