Equivalent Circulation Density Analysis of Geothermal Well by Coupling Temperature

Xiuhua Zheng,Zheng Yan,Zhiqing Wang,Hongyu Ye,Bairu Xia,Chenyang Duan

doi:10.3390/en10030268

Xiuhua Zheng, Zheng Yan + Show 4 more

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https://doi.org/10.3390/en10030268

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Abstract

The accurate control of the wellbore pressure not only prevents lost circulation/blowout and fracturing formation by managing the density of the drilling fluid, but also improves productivity by mitigating reservoir damage. Calculating the geothermal pressure of a geothermal well by constant parameters would easily bring big errors, as the changes of physical, rheological and thermal properties of drilling fluids with temperature are neglected. This paper researched the wellbore pressure coupling by calculating the temperature distribution with the existing model, fitting the rule of density of the drilling fluid with the temperature and establishing mathematical models to simulate the wellbore pressures, which are expressed as the variation of Equivalent Circulating Density (ECD) under different conditions. With this method, the temperature and ECDs in the wellbore of the first medium-deep geothermal well, ZK212 Yangyi Geothermal Field in Tibet, were determined, and the sensitivity analysis was simulated by assumed parameters, i.e., the circulating time, flow rate, geothermal gradient, diameters of the wellbore, rheological models and regimes. The results indicated that the geothermal gradient and flow rate were the most influential parameters on the temperature and ECD distribution, and additives added in the drilling fluid should be added carefully as they change the properties of the drilling fluid and induce the redistribution of temperature. To ensure the safe drilling and velocity of pipes tripping into the hole, the depth and diameter of the wellbore are considered to control the surge pressure.

Highlights

Proper wellbore pressure is the key to ensuring the drilling success
This paper modeled the temperature distribution by the Hasan model, and a simulation of sensitivity analysis was completed
The result indicates that the temperature of the drilling fluid in the bottom hole is much higher than the surface temperature; changing some parameters will lead to temperature redistribution in the wellbore

Summary

Introduction

Proper wellbore pressure is the key to ensuring the drilling success. When complex geological areas with multi-pressure systems need to be drilled, one of the severe challenges associated with drilling is to avoid drilling accidents, such as loss of circulation, blowout, or even collapse [1].Hydrothermal resources are buried in a tough but fractured formation, and the reservoir depth is shallow, which causes the deep formation pressure to be relatively low and the shallow formation pressure gradient to vary fiercely as well as being hard to control, drilling accidents are prone to occur [2]. The principal is to keep the annular pressure, which is usually expressed as the equivalent density, within the range of formation pore pressure and fracture pressure, i.e., pf < pa < pfrac. The annular pressures, such as static pressure, circulation pressure, initiating circulation pressure, viscous pressure and inertial pressure, are regulated through modifying drilling. Fluctuation pressure (surge and swag pressure) generated by a downward or upward pipe movement or running casing poses a great threat for safe drilling and induces lost circulation, kick and borehole collapse; the parameters that can control the fluctuation pressure are another problem to be studied

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