Three-dimensional physical simulation experiments on large-scale hydraulic fracturing in multi-thin interbedded tight sandstone reservoirs

The Linxing gas field on the northeastern edge of Ordos Basin is mainly composed of multi-thin interbedded tight sandstone reservoirs. These reservoirs feature complex lithologies and low permeability, and are affected by multiple factors with unclear mechanisms, leading to difficulties in hydraulic fracturing operations and significant variability in operation outcomes. Therefore, this study designed and conducted a series of large-scale three-dimensional (3D) physical simulation experiments of hydraulic fracturing under different geological conditions, focusing on different rock components, clay contents, particle sizes, sedimentary cycles, and planar and longitudinal heterogeneities of the tight sandstone reservoirs in the Linxing gas field. According to the similarity criteria, the basic parameters of the experiments were determined by referencing the triaxial geostress, rock strength, wellbore structural parameters, and on-site fracturing operational parameters of the Permian Shihezi Formation. Based on the characteristics of the main reservoirs in typical wells of the Linxing gas field, 15 cubic rock cores were produced to account for different rock components, clay contents, particle sizes, sedimentary cycle combinations, and planar and longitudinal heterogeneity combinations. Fifteen sets of hydraulic fracturing simulation experiments were conducted, and the main controlling factors affecting the propagation of hydraulic fractures were summarized by analyzing the injection pressure curves and observing the fracture surfaces of rock samples. The results indicate that rock minerals, particle sizes, sedimentary cycles, and planar and longitudinal heterogeneities have a significant impact on fracture propagation patterns in tight reservoirs. The fracture surfaces are more prone to buckling with larger sandstone particle sizes, weaker cementation, higher clay content, and stronger planar heterogeneity, increasing the expansion pressure and difficulty in sand addition. Sedimentary cycles facilitate hydraulic fractures to propagate along the cycle planes, resulting in horizontal fractures. The difficulty of breaking through in retrograde cycle interfaces is greater than in prograde cycles. Interfaces between sand and mud layers, sand and coal layers, and natural weak sandstone surfaces are easily activated, leading to "工" or "T" shaped fractures. A combination of "工", "T", and "十" shaped fractures may occur in sand-mud multi-thin interlayers. This experimental study reveals the propagation patterns of hydraulic fractures under different geological conditions, providing insights for research in similar blocks.