Dynamic Fracture Characterization and Integrated Optimization of Enhanced Oil Recovery Performance in Tight Formations under Uncertainty

对于被困在致密地层中的非常规资源，一次采收率非常低(约5-10%)，即使在钻完长水平井并进行了大规模压裂后也是如此。由于致密地层中的流体流动完全依赖于裂缝网络，而基质只起到了源泉的作用，因此迫切需要提高原油采收率的三次采油方法。室内实验和现场测试表明，注水开发一般不能达到常规油藏的预期开发效果，注气(如烃类气体、二氧化碳和氮气)注入，特别是吞吐工艺效果良好，优化注采方式对开发致密油和页岩气藏至关重要。物理上，裂缝网络、多尺度孔喉/裂缝结构和受限传质使致密地层中的渗流行为非常复杂。此外，水力压裂水平井的生产或注水会导致应力场的变化，从而导致基质渗透率和裂缝导流能力的变化。因此，在存在地质和经济不确定性的情况下，综合描述裂缝动力学特征，确定剩余油饱和度在基质和裂缝中的分布，优化油藏动态，对于设计技术可行、经济合理的致密地层三次采油方案和CO2储集能力具有重要意义。这项拟议研究的主要目标是：1)从实验和理论上量化注入气体-轻油体系的相态和双向传质；2)利用Micro-CT扫描图像重建的孔隙网络对基质和裂缝之间的复杂流动行为进行网络模拟；3)开发一种综合反演技术，通过执行瞬时压力/速度分析并结合监测和监测数据匹配生产历史来表征动态裂缝网络；以及4)开发稳健的并行优化器，以便在存在经济和地质不确定性的情况下有效地优化大型闭环系统。最后，我们将为石油和天然气行业提供一种集成和实用的技术，可用于准确量化相态和流体性质，表征动态裂缝网络，确定潜在的提高采收率机制，从而以经济高效和可持续的方式在具有复杂裂缝网络的致密地层中以经济高效和可持续的方式最大限度地提高石油采收率和二氧化碳储存能力。

The primary recovery factor is very low (around 5-10%) for unconventional resources trapped in a tight formation, even after long horizontal wells have been drilled and massively fractured. Due to its rapid depletion on primary energy, enhanced oil recovery (EOR) methods are urgently needed to boost production; however, it is still a challenging task to increase the ultimate oil recovery because fluid flow in tight formations can be completely dependent on the fracture network while the matrix only plays a source role. Laboratory experiments and field tests have shown that waterflooding does not normally result in the expected performance as in the conventional reservoirs, that gas (e.g., hydrocarbon gas, CO2, and N2) injection, especially huff-n-puff processes, performs favourably, and that optimization of production-injection modes is found to be fundamentally important to exploit tight oil and shale gas reservoirs. Physically, fracture network, multiscale pore-throat/fracture structure and confined mass transfer make flow behaviour very complicated in tight formations. Furthermore, production or injection through a hydraulically fractured horizontal well leads to changes in the stress field, and hence induces changes in matrix permeability and fracture conductivity. Therefore, it is essential to integrally characterize fracture dynamics, determine residual oil saturation distribution within matrices and fractures, and optimize reservoir performance in the presence of geological and economic uncertainty for designing a technically feasible and economically sound EOR scheme and CO2 storage capacity in a tight formation. The major objectives of this proposed research are: 1) to experimentally and theoretically quantify phase behaviour and two-way mass transfer for the injected gases-light oil systems; 2) to perform network modelling of complex flow behaviour between matrix and fractures with the reconstructed pore-network obtained by using the micro-CT scanning images; 3) to develop an integrated inversion technique to characterize dynamic fracture network by performing transient pressure/rate analysis and matching production history together with monitoring and surveillance data; and 4) to develop robust and parallelized optimizers to efficiently optimize large-scale and closed-loop nonlinear systems in the presence of economic and geological uncertainty. Finally, we will provide the oil and gas industry with an integrated and pragmatic technique that can be applied to accurately quantify phase behaviour and fluid properties, characterize the dynamic fracture network, identify the underlying EOR mechanisms, and thus maximize oil recovery and CO2 storage capacity in tight formations with complex fracture networks under uncertainty in a cost-effective and sustainable manner.