Abstract
The purpose of this paper is to discuss the variation of wellbore temperature and bottom-hole pressure with key factors in the case of coupled temperature and pressure under multi-pressure system during deep-water drilling circulation. According to the law of energy conservation and momentum equation, the coupled temperature and pressure calculation model under multi-pressure system is developed by using the comprehensive convective heat transfer coefficient. The model is discretized and solved by finite difference method and Gauss Seidel iteration respectively. Then the calculation results of this paper are compared and verified with previous research models and field measured data. The results show that when the multi-pressure system is located in the middle formation, the temperature of the annulus corresponding to location of the system is the most affected, and the temperature of the other areas in annulus is hardly affected. However, when the multi-pressure system is located at the bottom hole, the annulus temperature is greatly affected from bottom hole to mudline. In addition, the thermo-physical parameters of the drilling fluid can be changed by overflow and leakage. When only overflow occurs, the annulus temperature increases the most, but the viscosity decreases the most. When only leakage occurs, the annulus temperature decreases the most and the viscosity increases the most. However, when the overflow rate is greater than the leakage rate, the mud density and bottom-hole pressure increase the most, and both increase the least when only leakage occurs. Meanwhile, bottom-hole pressure increases with the increase of pump rate but decreases with the increase of inlet temperature. The research results can provide theoretical guidance for safe drilling in complex formations such as multi-pressure systems.
Highlights
Deep water drilling faces problems such as narrow formation pressure window and difficult pressure control
The temperature difference in other parts of the annulus is basically the same when the multi-pressure system is located in the middle formation
After circulating for 3 h, when the multi-pressure system is located in the middle formation or at the bottom hole, the variation of density and viscosity at different overflow and leakage rates is shown in Figure 13a–d, respectively
Summary
Deep water drilling faces problems such as narrow formation pressure window and difficult pressure control. Hasan–Kabir [9,10] established a model where variation of properties of drilling fluid with temperature and pressure was not considered, nor was the heat generated by drilling fluid flow taken into account, so there will be obvious errors in the calculation results. Established the wellbore and formation temperature calculation model when leakage was located in different position of stratum, but without considering the comprehensive influence of leakage and overflow and the coupled temperature and pressure [17]. There are many models for calculating wellbore and formation temperature under different conditions, there are few models that the effects of multi-pressure systems and coupled temperature and pressure are taken into account on wellbore temperature and pressure during circulation in deep water drilling.
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