微支撑剂对页岩油气的增产机理及选配原则

水力压裂是页岩油气增产的主要手段,其核心是向储层连续泵入压裂液迫使储层产生水力裂缝/缝网形成油气运移高效通道,从而达到油气增产的目的。相较人工主缝,微裂缝具有数量大、缝宽小、走向复杂等特点,常规支撑剂无法对其形成有效支撑,如何提高微裂缝的导流能力是进一步提高页岩油气产能的关键。微缝导流能力实验表明:微支撑剂嵌入页岩裂缝表面导致一定程度的渗透率损害,但支撑微裂缝的渗透率仍比页岩基质渗透率高出2～3个数量级,仍可为页岩油气运移提供有效渗流通道。本文系统分析了微支撑剂对微裂缝的支撑特性、微支撑剂的长距离输运性能及辅助降滤等特征,提出了微支撑剂对致密油气增产的内在机制。结合我国致密油气储层基质孔隙尺度,形成了考虑微裂缝开度及基质孔隙尺寸的微支撑剂选配原则。

Production enhancement mechanism of micro-proppant and its selection principles for shale oil and gas

Hydraulic fracturing is one of the major means of shale oil and gas reservoir stimulation, the core of which is to continuously pump fracturing fluid into the reservoirs to create hydraulic fractures/fracture networks and form efficient oil and gas migration channels, thus achieving the purpose of production increase of oil and gas. Compared with artificial main fractures, microfractures are characterized by large number, small width and complex trend, and cannot be effectively supported by conventional proppants. Therefore, how to improve the flow conductivity of microfractures is the key to further increase shale oil and gas productivity. Microfracture conductivity experiments show that micro-proppant embedding into the fracture surface of shale leads to a certain degree of permeability damage, but the permeability of supporting microfracture is still 2-3 orders of magnitude higher than that of shale matrix permeability, which can still provide an effective seepage channel for shale oil and gas migration. In this paper, the supporting characteristics of micro-proppants on microfractures, the long-distance transport performance of micro-proppants and the auxiliary filtration reduction characteristics are systematically analyzed, and the internal production enhancement mechanism of micro-proppants on tight oil and gas is proposed. In combination with the pore size of tight oil and gas reservoirs in China, the selection principle of micro-proppant considering microfracture opening and matrix pore size is formed, which can help enhance productivity of shale oil and gas wells.