Simulation research of field-scale hydraulic fracture extension mechanism based on XFEM

Abstract:

Hydraulic fracturing of hot dry rock（HDR） reservoirs to form a complex network of seams is essential for the construction of enhanced geothermal systems （EGS）. In order to deeply understand the mechanism of hydraulic fracture extension in HDR reservoirs and reveal the influence of engineering and geological parameters on hydraulic fracture extension， in this paper， a HDR reservoir in the Gonghe Basin of Qinghai Province is taken as the research object， and based on the extended finite element method （XFEM） numerical simulation software ABAQUS， a field-scale HDR reservoir model is established to realize the thermo-hydro-mechanical coupling and to analyze the extension mechanism of the hydraulic fracture. The results show that： （1） In the normal fracture-type stress state， the crack undergoes a very obvious turning toward the Z-axis， in the strike-slip-type stress state， the crack expands mainly along the horizontal direction with a slight tendency to turn toward the Z-axis， and in the thrust-type stress state， the crack expands along the horizontal direction. （2） With the increase of elastic modulus crack initiation pressure decreases， the injection pressure of crack extension also decreases； the larger the elastic modulus the earlier the crack initiation time； the larger the Poisson ratio the greater the rupture pressure of hydraulic cracks； the rupture pressure as a whole shows a normal fracture-type>strike-slip-type>thrust-type. （3） The hydraulic fracture rupture pressure decreases with the increasing temperature， by about 2~3MPa or so， showing the same trend for all three stress states. This paper inriches the numerical simulation methods of hydraulic fracturing extention for HDR， the relavant research results can also provides technical supports for the prediction of the hydraulic fracturing extention and the influences affected by different perameters for HDR reservoirs.

Key words:hydraulic fracturing;reservoir fracture;hot dry rock;extended finite element method;field scale;thermo-hydro-mechanical coupling