Study on temperature distribution of ultra-deep wellbore and its effect on mechanical properties of surrounding rock
ZHANG Jian1，2，LU Yunhu1，2
(1. State Key Laboratory of Petroleum Resources and Prospecting，China University of Petroleum(Beijing)，Beijing，102249，China；2. College of Petroleum Engineering，China University of Petroleum(Beijing)，Beijing，102249，China)
Abstract：After the drilling fluid stops circulating，the bottom hole temperature rises again，which is very easy to cause delayed damage of the wellbore rock caused by the temperature rise. The wellbore instability caused by the change of wellbore temperature during drilling fluid circulation was analyzed. Firstly，the influence of time and engineering parameters on the temperature distribution of wellbore was studied by numerical calculation method based on unsteady temperature distribution. In addition，the strength experiments of fine sandstone at different temperatures were carried out by means of high temperature and high pressure rock mechanics testing machine，and the influence law of temperature change on rock strength was researched. The experimental results show that after drilling fluid circulation，the temperature near the wellhead increases with time，and the temperature near the bottom of the well decreases with time，and there exists a critical well depth related to time. The temperature changes mainly concentrate in a small area near the wellbore，and the temperature decreases rapidly in the initial stage of drilling fluid circulation；the larger the displacement，viscosity and density of drilling fluid，the greater the decrease of wellbore temperature near the bottom hole，and the change of displacement has the most obvious effect on the temperature distribution of wellbore；the temperature increases，which aggravates the damage degree of fractured rock samples and eliminates slip damage. With the occurrence of cross-section failure and end-face failure，in the fracture dip-compressive strength diagram，the influence of temperature rise on the slip area is not obvious；with the increase of temperature，the compressive strength of rock sample decreases obviously，and the stress-strain curve becomes tortuous，there are obvious plastic deformation sections，and the failure process becomes complex.
张 健1，2，卢运虎1，2. 超深井筒温度分布及其对围岩力学性质的影响研究[J]. 岩石力学与工程学报, 2019, 38(S1): 2831-2839.
ZHANG Jian1，2，LU Yunhu1，2. Study on temperature distribution of ultra-deep wellbore and its effect on mechanical properties of surrounding rock. , 2019, 38(S1): 2831-2839.
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2019, Vol. 38 
