Study On Geomechanical Properties Of Shallow Shale Gas Reservoir In Zhaotong

Unlike conventional reservoirs,unconventional shale gas reservoirs have low porosity and permeability,requiring large-scale volumetric fracturing to form complex fracture networks to achieve stable production.Therefore,it is necessary to accurately grasp the mechanical properties of reservoir rock and effectively evaluate the reservoir fracability.At present,the brittleness of rock mechanics analysis is mainly used as the evaluation standard of fracability at home and abroad,but brittleness cannot well represent the mechanical properties of reservoir and the ability to form complex fracture network.Therefore,the evaluation of the reservoir needs to combine more geomechanical properties,such as the development degree of natural fractures,in-situ stress and anisotropy of the reservoir.In southern sichuan basin on Zhaotong block ordovician text group-the dragon of lower Adakite creek shallow shale gas reservoir thickness of high silica content,high quality,organic carbon resource potential is huge,is our country the main shale gas fracturing zone,but also has a shallow,complex structure,large dip Angle,etc,in the process of hydraulic fracturing cracks extension is more complicated,It is necessary to accurately grasp the mechanical properties of reservoir rock.Therefore this research Zhaotong blocks to five mountains,dragon creek reservoir as the research object,based on laboratory data,well logging and geological data,fracturing and production data,Zhaotong shallow shale gas geological mechanics properties,the hydraulic fracture extension study of the main controlling factors and seam formation ability and provide guidance for engineering measures.The results are as follows:1 There are great differences in mechanical properties in the study area as a whole,with low compressive strength and Young’s modulus and medium Poisson’s ratio;The pore pressure in the study area is high,with pore pressure coefficients ranging from 1.1to 1.47.2 Dynamic and static transformation relationship in the study area E _static=0.71E _dynamic+0.99,Pr _static=0.89Pr _dynamic+0.013 Due to the great variation of buried depth,the variation range of in-situ stress value is large;The horizontal stress difference of Q1 is at least 3～4MPa.The interlayer stress difference is small,and Longyi ₁¹and Longyi ₁² reservoirs are the smallest,which is conducive to longitudinal fracture penetration.In addition,the difference between the overall vertical stress and the minimum horizontal stress is small,and some areas belong to the critical value of strike-slip fault and reverse fault,which is conducive to the development of shear fracturing.4 Microfractures are well developed in the samples as a whole,and horizontal fractures and bedding are well developed in the reservoir,which are easy to fracture along the bedding.Development degree of bedding and horizontal micro-fracture in each well S7>S8>Q1,Longyi ₁¹,Longyi ₁² bedding and horizontal microfractures are the most developed in the interbedded strata,followed by Wufeng Formation Longyi ₂.The overall brittleness is good,quartz feldspar mineral composition is more brittle S8>Q1>S7 is the best,and the rest are next.5 The main controlling factors affecting fracture propagation in Zhaotong Haiba shallow shale gas reservoir are stress difference,strength,fracture and brittleness.Combining the above data,the seam forming capacity Q1>S8>S7,Longyi ₁¹and Longyi₁² have the best sewing capability.