Propagation of hydraulic fractures in thin interbedded tight sandstones

Thin interbedded tight sandstone reservoirs are characterized by strong vertical heterogeneity due to the superimposed pattern of the deposited sandstones and mudstones. As a result, hydraulic fractures are difficult to propagate vertically to effectively connect the reservoirs. Given this, ascertaining the vertical propagation patterns of hydraulic fractures in thin interbeds is of great significance for the development of thin interbedded tight sandstones. With the thin interbedded tight sandstone reservoirs of the lower Shihezi Formation in the Linxing block, Ordos Basin as a case study, this study built the fracture propagation model of these sandstones. Accordingly, it analyzed the effects of geological factors (i.e., the stress difference between reservoirs and interlayers, the thicknesses of reservoirs and interlayers, and rock mechanical properties) and engineering factors (i.e., the viscosity and injection rate of fracturing fluids) on the propagation of hydraulic fractures. Moreover, this study verified the reliability and accuracy of the model based on field hydraulic fracturing performance and microseismic monitoring data. The results of this study are as follows: (1) The stress difference between reservoirs and interlayers and the thicknesses of reservoirs and interlayers were the major geological factors affecting the vertical propagation of hydraulic fractures, which was restrained when the stress difference was greater than 4 MPa. (2) The interlayers with high elastic moduli were conducive to the vertical fracture propagation. (3) Poisson’s ratio almost had no effect on vertical fracture propagation. (4) The viscosity of fracturing fluids had little effect on the propagation. (5) The injection rate of fracturing fluids promoted vertical fracture propagation, which, however, slowed down when the injection rate increased to a certain extent. Different stress differences corresponded to different optimal displacements. Therefore, factors that can effectively promote vertical fracture propagation during the hydraulic fracturing of thin interbedded tight sandstones include small thicknesses of reservoirs and interlayers, small stress differences between reservoirs and interlayers, high elastic modulus, and high injection rate. The results of this study will provide a theoretical basis for the hydraulic fracturing design of similar sandstone reservoirs.