Vertical Extension Of Hydraulic Fracture Of The Bedding Shale Formation

Shale gas formation is a low permeability reservoir which have got different natural fractures and bedding plane distributions.Stimulation by hydraulic fracturing is a big challenge,so it is still needed technical recommendations to end up with the best stimulation results.Despite of several researches done on shale gas reservoirs,little or no attention has been paid on the vertical extension of hydraulic fracture of the bedding shale formation.Therefore the present study intends to experimentally investigate the factors which influence vertical extension of hydraulic fractures as well as numerical simulation of hydraulic fracturing in layered shale formation in optimizing the performance of hydraulic fracturing program in the bid to increase well production.To conduct this work,Square specimens of 0.3m x 0.3mx 0.3m from Long Maxi shale outcrops in China,a true tri-axial pressure machine and a servo hydraulic pump of MTS 816 was used.The experiment was planned to study the influential factors which are Differential stress,Fluid viscosity,Flow rate as well the influence of bedding plane.Furthermore,numerical simulation was used to analyze and study the effect of stress distribution and material properties on hydraulic fracture propagation in a layered shale formation by using COMSOL MULTIPHYSICS as well as modeling of hydraulic fracture propagation across the layers using ABAQUS by studying the influence of Flow rate,Stress contrast between layers and Young modulus.It is observed experimentally that,hydraulic fracture would cross the beddings under high horizontal stress difference of 12 MPa and would propagate along the beddings under low horizontal stress difference of 3MPa,hydraulic fracture propagated in vertical direction with single and large width fracture at high fluid viscosity and high flow rate of 120 m Pa.s and 1.00ml/s respectively.The combined effect of flow rate and viscosity resulted to single main fracture for 1.0ml/s and 120 m Pa.s,complex fracture network system for 0.166ml/s and 3m Pa.s,planar fracture for 0.166ml/s and 120 m Pa.s and complex fracture for 1.0ml/s and 3m Pa.s.The results from Comsol numerical simulation revealed that,a layered formation with different material properties and thickness have minimum horizontal stress contrast between layers and the deformation appeared in layers with the higher value of Poisson's ratio and less young modulus.Under simulation of vertical fracture propagation,high stress difference of 6 MPa resulted to fracture large width with small vertical extension path while 2MPa stress difference fracture can effectively penetrate the layer with large length.For the case of flow rate,vertical extension path and width increased with the increase in fluid flow rate with recommended flow rate of less than or equal to 3m^3/min at initial stage and change to higher flow rate at the fracture growth stage.When the young modulus of inter layer increased to 46 GPa,the fracture width is small while height is larger for the same stress contrast and same injection rate.The smaller the inter layer moduli,vertical extension of hydraulic fracture gets more difficult.Therefore to acquire large vertical extension avoid perforation in the thick inter-layers near the reservoir.Due to the parameter used for the field simulation,it was observed that,the pore pressure in shale 1 and shale 2 is large than the pore pressure in the interlayer.During hydraulic fracture propagation,the hydraulic fracture vertically crosses the inter layer with its tip in underlying and overlying strata.The width of hydraulic fracture in the interlayer observed to be smaller than in the pay zone layers.Hydraulic fracture extended vertically about 10.58 m high with an approximately 45 m length and 1.62 mm width for shale 2 and an approximate of 37.5m length with 1.23 mm width for shale 1.These research findings can be used for field engineering problem analysis,and not only for the layered formation but also used to explain different behaviors of hydraulic fracture during intersection with natural fractures.