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，即使在钻了长水平井并进行了大规模压裂之后，其初级采收率也非常低（约为5-10%）。由于一次能源的快速枯竭，迫切需要提高石油采收率（EOR）的方法来提高产量；然而，提高最终采收率仍然是一项具有挑战性的任务，因为致密地层中的流体流动完全取决于裂缝网络，而基质仅起来源作用。实验室实验和现场测试表明，水驱通常不能达到常规油藏的预期效果，而注气（例如碳氢化合物气、CO2和N2），特别是吞吞活吸过程，表现良好，并且发现生产注入模式的优化对于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得致密地层的流动行为非常复杂。此外，通过水力压裂水平井进行生产或注入会引起应力场的变化，从而引起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，全面表征裂缝动态、确定基质和裂缝内残余油饱和度分布、优化储层性能，对于设计技术上可行、经济上合理的提高采收率方案和致密储层的二氧化碳储存能力至关重要。******本研究的主要目标是：1)从实验和理论上量化注入气轻油系统的相行为和双向传质；2)利用微ct扫描图像重建孔隙网络，对基质与裂缝间复杂流动行为进行网络建模；3)开发一种综合反演技术，通过进行瞬态压力/速率分析，将生产历史与监测数据相匹配，来表征动态裂缝网络；4)开发鲁棒并行优化器，以有效地优化存在经济和地质不确定性的大型闭环非线性系统。最后，我们将为油气行业提供一种综合实用的技术，该技术可用于精确量化相行为和流体性质，表征动态裂缝网络，识别潜在的EOR机制，从而在具有复杂裂缝网络的致密地层中以经济有效和可持续的方式最大化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.