Experimental Evaluation And Application Of Conglomerate Mechanical Properties

The rock mechanics properties of conglomerate reservoirs are important basic data for conglomerate oil and gas resource evaluation,reservoir simulation and oil and gas well engineering design.However,due to the complex rock structure of conglomerate,its mechanical properties show significant heterogeneity and discreteness,which bring great difficulties to safe drilling and effective fracturing of conglomerate reservoirs.In view of this,this thesis takes the conglomerate of Baikouquan Formation in M area as the research object,and studies the main controlling factors affecting the mechanical properties of conglomerate,and explores the evaluation method of conglomerate mechanical properties,and applies this evaluation method to the logging calculation model of rock strength parameters of conglomerate formation.The logging profiles of rock strength parameters of conglomerate strata are studied.Finally,combined with the wellbore stability theory,based on this evaluation method,the safety drilling fluid density window of conglomerate formation is analyzed to guide the drilling design.The conclusions are as follows:(1)Through indoor rock mechanics experiments,it is found that the gravel strength inside the same conglomerate in M area is heterogeneous,but the distribution of gravel strength between different conglomerates is statistically similar,the hardness concentrating in 408?788 MPa;The difference between the strength of the gravel and the matrix in the conglomerate is significant,the average ratio of the indentation hardness of the gravel to the matrix is about 2.3,and the average ratio of the indentation modulus is about 3.6.(2)Numerical simulation experiments show that the uniaxial compressive strength and elastic modulus of conglomerate are positively correlated with the cementation strength,gravel strength and gravel size,but negatively with the gravel content and conglomerate sample size;There is a threshold for the influence of gravel strength on conglomerate strength,and the corresponding gravel strength threshold in the thesis is 147 MPa.When the gravel strength is exceeding this threshold,the conglomerate sample's strength will not increase anymore;The influence of conglomerate sample size on conglomerate strength also has a threshold value,which is called the characteristic size of conglomerate,and the corresponding uniaxial compressive strength of the conglomerate is called the characteristic strength of the conglomerate.(3)The physical experiments and numerical simulation experiments show that the strength of conglomerate has obvious scale effect.By analyzing the results of previous physical and numerical simulation,it is found that the conglomerate strength and conglomerate size are in accordance with the exponential decay law.Based on this,the conglomerate mechanical property evaluation model is established.that is ?=ae-bD.The relationship between fitting parameter values a,b,c and gravel diameter in the evaluation model of conglomerate mechanical properties is studied,and the applicability of the evaluation model of conglomerate mechanical properties is also improved.The average error between the conglomerate strength calculated by this method and that got by numerical simulation is 5.34%,which can meet the engineering needs.(4)The characteristic size of conglomerate is related to the gravel diameter.The results show that the larger the gravel diameter in conglomerate,the larger the characteristic size of conglomerate;And a conglomerate characteristic size chart is formed for the studied area.Based on physical and numerical experiments,an experiment evaluation method is build for conglomerate,which is of great importance for the coring and mechanical experiments of conglomerate formation.(5)Based on the evaluation method of conglomerate mechanical properties,the logging calculation model of conglomerate strength parameters is obtained.The logging profiles of rock mechanics parameters of drilled wells show that the strength parameters of conglomerate calculated by this method are lower than those obtained by conventional methods,while the strength parameters obtained of the mudstone and sandstone sections are not quite different.(6)Combined with the wellbore stability theory,the fluid density of safe drilling of drilled wells indicates that the collapse pressure equivalent drilling fluid density of the conglomerate section obtained by this method is higher than that obtained by the conventional method,while the density of the fracture pressure equivalent drilling fluid in the conglomerate section is lower than that obtained by the conventional method.The logging profiles of collapse pressure obtained by this evaluation method is consistent with the well diameter expansion curve,and the fracture pressure of the formation is close to the fracture pressure of the fracture obtained by the fracturing data,which reflects the reliability and scientific advancement of the evaluation method;Therefore,for conglomerate with complex structure,the evaluation method established in this paper will provide reliable technical parameters for the safe drilling and effective fracturing reconstruction of conglomerate formation,which are of great significance for accelerating the exploration and development of conglomerate oil and gas resources and ensuring national energy security.