A Study On The Fracture Height Propagation Of Volume Fracturing In Jimsar Multi-Layer System

The Lucaogou Formation in the Jimsar Sag is a typical continental shale reservoir.The reservoir lithology is complex,with centimeter-level interbedding vertically,with well-developed interlayers and high-frequency interbedding features with production layers,shale bedding,etc.Natural structural planes are developed,and multiple factors restrict the vertical propagation of fractures.It is particularly important for fracturing and stimulation of multi-reservoir shale reservoirs to clarify the vertical propagation law of fractures and enhance the vertical propagation ability of fractures.Through the combination of laboratory experiments and numerical simulations,this paper explores the influence of interlayers and developed bedding on the vertical propagation of fractures,and analyzes the applicability of the existing volume fracturing technology to realize the vertical production of shale oil multi-reservoir.The main work and conclusions are as follows:(1)The rock properties are tested on the outcrops on site,and the test results are used for subsequent numerical simulations.The multi-layer rock sample fracturing physical model experiment was carried out.The experimental results show that when the vertical stress difference is low,the bedding is easily activated to form step fractures;Deflection occurs;high displacement helps to increase the net pressure in the fracture,helping the fracture to break through the interlayer limit.(2)Based on the CZM model in the ABAQUS platform,the interactive simulation of hydraulic fractures and bedding is carried out.The results show that the smaller the bedding dip angle is,the easier the bedding is to be activated;the vertical stress directly affects whether the bedding can be activated or not.When the effect becomes weaker,the bedding is less likely to be activated;for the bedding with a large dip angle,when the vertical stress is large,it is difficult to activate even if the shear strength is small;the highviscosity fracturing fluid is beneficial to increase the net pressure in the fracture,Forcing cracks directly through the bedding.(3)Based on the CZM model in the ABAQUS platform,the vertical fracture propagation simulation under reservoir and interlayer conditions is carried out.The results show that the horizontal in-situ stress contrast is the most important factor restricting the vertical propagation of fractures.If the horizontal in-situ stress contrast is greater than 4MPa,the vertical limitation of fractures is serious;the elastic modulus affects the vertical propagation of fractures,and the formation with small modulus has a certain effect on the vertical propagation of fractures.After the fracture passes through the interface,a larger elastic modulus is conducive to the vertical propagation of the fracture;when the interlayer is perforated,it is easy to form a fracture shape with wide ends at both ends and narrow in the middle.Under the same formation parameters,the obtained fracture height larger;the effect of hydraulic fracturing in the middle of the reservoir is better than that in the deviation from the middle.(4)Based on the SHG model of the PETREL platform,the sensitivity analysis of fracturing parameters is carried out.The results show that high displacement,small cluster spacing,and appropriately increasing the proportion of high-viscosity slick water can help strengthen the vertical stimulation effect of fracturing.