中—低成熟度页岩油藏原位转化热-反应流耦合数值模拟

中国陆相页岩油储量丰富,成熟度整体偏低,储层中包括已生成的滞留烷烃和未转化的固体有机质,可动用能力差,且地层能量不足,仅依靠常规压裂改造技术难以获得经济产量,必须采用地下原位加热转化技术才能有效开发。伴随地层加热,干酪根与滞留烷烃发生多级平行化学反应,流体组成与储集空间均发生较大变化,使得原位转化过程中的热-反应流耦合机制更加复杂。对此,通过考虑原位转化过程中的干酪根分解、烷烃裂解对油气组成以及岩石孔渗参数的影响,建立了页岩油藏原位转化热-反应流耦合数学模型及数值求解方法。通过数值算例验证了数学模型的正确性,分析了加热温度、加热模式、初始干酪根浓度等参数对开发效果的影响,并从经济效益的角度评价了页岩油藏原位转化开发的可行性。从热-反应流角度分析了页岩油藏原位转化过程,提出的模型和计算方法可用于评估页岩油藏原位转化过程的开发效果,并为中—低成熟度页岩油藏的高效开发提供理论支持。

Numerical simulation of thermal-reactive flow coupling during the in-situ conversion of medium to low maturity shale reservoirs

China’s onshore shale oil reserves are abundant with low maturity on the whole. The reservoirs include the remained hydrocarbons and unconverted solid organic matter, which have poor producing ability and insufficient formation energy, thus making it difficult to obtain economic yield only by conventional fracturing transformation technology. Therefore, in-situ underground heating and conversion technology has to be applied for effective exploitation. Along with the formation heating, multi-stage parallel chemical reactions occur between kerogen and retained hydrocarbons, and the fluid composition and reservoir space both change significantly, as a result of which the thermal-reactive flow coupling mechanism in the in-situ conversion process becomes more complex. For this problem, considering the effects of in-situ conversion decomposition of kerogen and hydrocarbons cracking on fluid composition and rock pore-permeability parameters, the authors establish a mathematical model of thermal-reactive flow coupling during the in-situ conversion of shale reservoirs and a numerical solution method. The validity of the mathematical model was verified by numerical calculations, the effects of heating temperature, heating pattern, initial kerogen concentration and other parameters on the development effect were analyzed, and the feasibility of exploitation by in-situ conversion of shale reservoirs was evaluated from the perspective of economic benefits. The in-situ conversion process of shale reservoirs was analyzed in terms of the thermal-reactive flow, and the proposed model and calculation method can be used to evaluate the development effect of in-situ conversion process of shale reservoirs and provide theoretical support for the efficient development of medium to low maturity shale reservoirs.