Mechanical Experiment Of Ultra-deep Carbonate Rock And Research On Collapse Pressure Of Well

Wellbore stability has always been the focus of research by scholars at home and abroad.Wellbore collapse not only restricts oil and gas development,but also causes a series of engineering accidents.For the ultra-deep fractured carbonate reservoir in the northwest of China,the reservoir has deep burial depth,high temperature,random development of microfractures,and weak cementation between the fractures,so the phenomenon of wellbore collapse is particularly obvious.The study of wall stability is becoming more and more important.In order to fully understand the instability mechanism of the wellbore and determine a reasonable production system and development plan,this paper carried out rock mechanics strength experiments in different environments for the reservoir core of the target well,combined with Mohr-Coulomb Strength-weak-surface theory,based on rock mechanics theory and finite element numerical simulation methods,a mathematical model of carbonate reservoir wellbore collapse pressure was established,and the collapse pressure profile of the target well was constructed,which provided a theoretical basis for formulating a reasonable production system.The main research contents are as follows:(1)Triaxial mechanical strength experiments under different temperature and pressure conditions were carried out.The experimental results showed that as the temperature increased,the Young's modulus of the rock decreased,the Poisson's ratio increased,the internal friction angle decreased,and the cohesive strength increased.(2)The rock mechanical strength experiment after immersion in the completion fluid and the acid solution was carried out,and compared the characteristics of rock mechanical parameters before and after immersion in the working fluid.The results showed that all mechanical parameters of the rock after immersion were reduced.The relationship between rock strength before and after immersion was unsoaked > completion fluid immersion > acid immersion,which provided experimental data for subsequent theoretical modeling.(3)Based on the theory of rock mechanics,a mathematical model of the wellbore collapse pressure considering the weak surface of the fracture was established.Combined with the finite element numerical simulation method,a numerical simulation of the wellbore collapse pressure with the weak surface of fracture was carried out,and the wellbore collapse pressure of ultra-deep high-temperature carbonate reservoirs was predicted.(4)Based on the acoustic full-wave logging curve,using the logging response method,the in-situ stress profile of the reservoir was obtained,and combined with the rock strength criterion,the reservoir collapse pressure profile of the target well was constructed,which provided guidance for the development of a reasonable production system.