Effect Of Rock Formation Properties On Vertical Propagation Of Volume Fractures

Unconventional oil and gas reservoirs have the characteristics of low porosity and low permeability,and large-scale volume fracturing or horizontal well staged fracturing is required to produce productivity.Large-scale volume fracturing is conducive to fracture propagation in the longitudinal direction.If the stress difference between layers is insufficient,the fracture height may be out of control.The development of bedding and natural fractures makes it easy to lose energy along the bedding,hinder the vertical expansion of fractures,and develop high-quality reservoirs by staged fracturing of horizontal wells.When high-strength barriers are developed,the vertical expansion height of volumetric fractures may be high.Not as big as expected.In short,whether the seam height is out of control or the seam height is insufficient will affect the transformation effect.At present,the mechanism and laws of hydraulic fracturing crack propagation in the vertical direction are unknown.Therefore,it is necessary to study the influencing factors and laws of hydraulic fracture vertical expansion under volume fracturing conditions,so as to provide a reference for optimizing hydraulic fracturing construction.In this paper,the tight sandstone of Linxing block is taken as the main research object,and the Jilin shale oil shale in Songliao Basin and the shale gas shale of Longmaxi Formation in Sichuan are taken as comparative research objects.The impact of expansion.First,the basic physical properties and important mechanical parameters of the reservoir were obtained through laboratory experiments,and the conversion relationship between dynamic and static elastic modulus was established to correct the dynamic elastic parameters obtained by logging data.Secondly,based on the spring model and logging data,through hydraulic fracturing closure stress,the structural stress coefficient of the reservoir,the rock mechanical parameters of the continuous formation and the ground stress were obtained,and the stress difference of the reservoir and the mechanical properties of the reservoir rock were analyzed It affects the vertical propagation of hydraulic fractures and provides important sensitive parameters for numerical simulation of hydraulic fractures.Then the numerical simulation was used to study the influence of parameters such as Young's modulus,Poisson's ratio,interlayer stress difference and construction displacement on the vertical expansion of hydraulic fractures.Finally,combined with on-site fracturing construction and post-fracturing productivity,the effects of different reservoir fracturing reconstructions were analyzed,and the main controlling factors for the vertical expansion of volume fracturing fractures in Linxing block were obtained.The research results show that the main factors affecting the vertical expansion of fractures are as follows:(1)rock mechanical properties,anisotropy,bedding,microfracture development degree,natural fracture development degree;(2)elastic modulus and porosity of the barrier Pine ratio,and thickness of barrier;(3)Stress difference of reservoir/barrier;(4)Construction parameters.Among them,the stress difference between the target layer and the upper and lower barriers is the most important factor affecting the vertical propagation of fractures.When the stress difference of the reservoir barrier is too small,vertical fractures can easily penetrate the barrier and cause energy loss,making it difficult to target the target Extend stitching.The second is the construction displacement,Young's modulus of rock formation,Poisson's ratio and other parameters.Comparing the shale oil in Jilin with the shale gas in Longmaxi,Sichuan,the stress difference of the interlayer in the tight sandstone of the Linxing block is less than3 MPa.During large-volume volume fracturing,hydraulic fractures are prone to penetrate the layer,in the vertical It is easy to over-expand and affect the fracturing effect.It is recommended that for the insufficient stress difference between the layers of the LX-?well in Linxing block,the construction displacement can be controlled to change the fluid pressure in the fracture,or the artificial barrier measures can be taken to indirectly change the stress difference of the reservoir,or add temporary blocking The agent makes the cracks turn during the expansion process,forming new branch cracks,so as to finally achieve the purpose of improving the fracturing effect.