关键词: 页岩油, 水力压裂, 焖井压降, 缝网特性, 特征曲线, 诊断图版

Abstract: It is common to shut in shale oil fractured wells for a period of time before production, during which the wellhead pressure exhibits different declining characteristics; moreover, there is a lack of fast and effective diagnostic and analytic methods for the correlation between the pressure drop characteristics of shut-in wells and the properties of fracture networks. For this reason, a set of shut-in pressure drop models is firstly proposed for shale oil fractured horizontal wells, and the shut-in pressure drop derivative curves obtained from the simulation show the morphological characteristics of W-shape in double logarithmic coordinates, reflecting the scale, storage capacity and flow conductivity of the primary and secondary fractures. The sensitivity simulation results show that the length and flow conductivity of the primary fractures have a weak influence on the pattern of pressure drop derivatives, and only affect the start time of the W-shaped curve; by contrast, the density, width and permeability of the secondary fractures have a significant impact on the pattern of pressure drop derivatives, and determine the depth, proportion, and duration of the two V-shaped curves. On the whole, the pressure drop derivative curve of the fracture network dominated by storage capacity is characterized by "W-shape with shallow concave and convex on the upper right side", while the pressure drop derivative curve of the fracture network dominated by flow conductivity is characterized by "W-shape with deep concave and convex on the lower left". In addition, a fracture network diagnosis chart was plotted according to the simulation results, and a diagnostic analysis method for fractured networks of shale oil wells was set up based on the characteristic curve of shut-in pressure drop. Finally, based on the shut-in pressure drop data of 12 typical fractured wells in Jimsar shale oilfield in Xinjiang, we conducted comparative analysis of the fracturing effect of single/platform wells, and interlayers/interwells, found the parameter combination of scale and properties of primary and secondary fractures of the wells, and completed the fitting and inversion of the key fracture network parameters, thus providing a theoretical basis for the comprehensive evaluation of the fracturing effect of horizontal wells in shale oilfield.

Key words: shale oil, hydraulic fracturing, shut-in pressure drop, fracture network characteristics, characteristic curve, diagnosis chart