富有机质页岩储层热激致裂增渗的有利条件

页岩气藏的经济开发成为了当前非常规天然气开发关注的焦点。页岩气藏开发方式以"水平井+水力压裂"为核心技术,水力压裂过程中存在"大量压裂液滞留储层,难以返排,形成水相圈闭损害,阻碍气体产出"的工程难题。此外,水力压裂能形成大规模复杂缝网,沟通了微米级裂缝,而基块纳米级孔隙中气体仍然难以进入裂缝。从室内实验和矿场试验两方面概述了储层高温热处理的研究进展,提出了与水力压裂技术协调的富有机质页岩储层热激致裂的方法,从页岩储层地质特征与工程实际分析了页岩储层适合热激增渗的有利条件。研究认为,热激条件下有机质生烃增压、丰富多样的矿物组分差异热膨胀、微米-纳米级孔隙压力仓作用是页岩热致裂的有利地质条件;基于页岩气井体积改造形成的裂缝网络,滞留压裂液不仅能提高页岩导热能力,且在热激条件下水热增压、热液溶蚀作用可为页岩致裂增渗提供重要的工程条件。充分利用页岩储层独特的地质优势和有利的工程条件,包括热液作用、矿物组分非均匀膨胀致裂和热促吸附气解吸的热激法对压裂后的页岩储层进行改造,能够有效缓解甚至解除水相圈闭等储层损害,促使水力裂缝或天然裂缝两侧基质岩石热致裂,改善裂缝网络,增强页岩储层基质-天然缝-人工缝多尺度传质能力,同时实现压裂液的回收再利用,这将是一种环境友好型的有效开发页岩气藏的新方法。

Advantages of thermal stimulation to induce shale cracking after hydraulic fracturing over organic-rich shale reservoirs

The economic development of shale gas reservoirs has become the focus of current unconventional gas development. The development method of shale gas reservoirs is based on "horizontal well and hydraulic fracturing" as the core technology. In the process of hydraulic fracturing,a great amount of fracturing fluids retain in the reservoirs,which are difficult to flowback,forming water phase trap damage and hindering gas production. In addition,large-scale complex fracture networks formed by hydraulic fracturing can communicate micron-scale cracks,but it is still difficult for gas in the nano-scale pores of the matrix to enter the crack. This paper proposes a method for thermal stimulation to cause shale cracking coordinated with hydraulic fracturing technology over organic-rich shale gas reservoirs. The research progress of formation heat treatment is summarized from the aspects of laboratory experiments and field tests. In terms of the geological characteristics and engineering technologies,the advantages of this method over organic-rich shale gas reservoirs are also analyzed. It is considered that the role of hydrocarbon-generating overpressure,different thermal expansion coefficients of minerals as well as pressure compartments formed by micro-nanoscale pores provides the favorable factors. Based on the fracture network formed by application of the stimulated reservoir volume,the retaining fracturing fluids can enhance the heat transfer area of shale. Aquathermal pressuring and hydrothermal fluids at certain temperature can also contribute to thermal fracturing. By making full use of the unique geological superiorities and favorable engineering conditions of organic-shale gas reservoirs,this method will effectively transform the shale gas reservoirs after hydraulic fracturing,which can obviously alleviate or even eliminate water trapping damage,promote thermal cracking of matrix rocks on both sides of hydraulic fractures or natural fractures and finally improve the multiscale gas transport ability from matrix-natural fracture-artificial fracture network of shale. Meanwhile,with increasing temperature,the recovery and utilization of flowback fluids can be realized and it will be an environment-friendly new method for the effective development of shale gas reservoirs.