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Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

Wellbore Temperature Profile Calculation and Hydrate Formed Region Prediction when Drilling
Horizontal Wells to Deepwater Reservoirs
Chao Fu1, Jin Yang1, Xiao Wang2, Wenlong Li2, Mengjie Lu1, Lei Li1, Minghe Zhang1
1, China University of Petroleum, Beijing, China;
2, CNOOC China Limited, Tianjin Branch, Tianjin, ChinaABSTRACT
In deepwater drilling operations, natural gas may enter the wellbore fromoil reservoirs. As the wellbore and pipelines in deepwater wells are under
low-temperature and high-pressure conditions, natural gas hydrates areeasy to form, which will bring new problems and challenges to drilling,
well control and riser design. When drilling a horizontal wellhole, theheat transfer mode in openhole section will change, for the existence ofopenhole section. In this paper, a model to calculate the wellbore
temperature profile when drilling horizontal wells to deepwater
reservoirs is established, considering the effects of openhole. A casestudy is carried out, based on which, the wellbore temperature profileand the hydrate formed region are depicted. The sensitivity analysis
about parameters including horizontal section length, water depth,
geothermal gradient, mud parameters and additives are also presented.
According to the equilibrium curve and annulus temperature curve,
hydrate formed region is affected significantly by water depth, mudspecific heat capacity and additives. Horizontal section length andgeothermal gradient only have little influence on hydrate formed region.
This study will provide certain guidance for engineering practice ofdeepwater drilling.

𝑞𝑎𝑒 , 𝑞𝑎𝑝=𝜙=

Enthalpy flow from/to the small segment in drillpipes ,annulus
Heat transferred from annulus to environment anddrillpipes
Heat transferred from fluid to the pipe surfaceℎ=Convective heat transfer coefficient𝑆=

Convection transfer area

∆𝑇=

Temperature difference𝑇𝐷=

𝑈𝑎 , 𝑈𝑝=Time functuion
Overall heat transfer coefficient in annulus anddrillpipes

Heat specific capacity of mud , rock𝜌𝑠 , 𝜌𝑚=Density of rock , mud𝑃

=Pressure of wellbore

𝑘𝑐𝑒𝑚=Heat conductivity of cement

𝑇𝑠𝑒𝑎 , 𝑇𝑒=

Temperature of sea , environment𝑡𝐷=Dimensionless time

Temperature profile is one of the most important parameters whendrilling a well, for it will affect the downhole pressure and lead to thewellbore stability problems. In deepwater drilling, the temperature of sea
water decreases with the water depth and will cool the drilling fluid, andthen formation temperature increases with depth and heat the fluid. As
known, gas hydrate will form under conditions of high pressure and lowtemperature. The temperature/pressure condition in annulus makes it
easy to form gas hydrate which will lead to serious accidents whendrilling in deepwater environment (Barker and Gomez 1989). Therefore,
the wellbore temperature profile should be calculated accurately and theoccurrence of hydrate accumulation should be predicted in advance.
However, the temperature of drilling fluid will be difficult to determine,
especially when drilling horizontal wells into deepwater sediments.
Many researchers studied about the temperature and pressure profile ofdrilling and production wellbore. Ramey (1962) gave the classicalsolution of temperature profile when injecting hot fluid into a wellhole,which has a far-reaching influence on subsequent relevant studies. Hasanand Kabir (1996) deduced the wellbore temperature profile in vertical
gas-lift wells and gave an analytical solution. Wang, Hao et al. (2010)
established a coupled model of wellbore temperature profile whendrilling in deepwater, considering the effects of temperature and pressure
on the characteristics of drilling fluid. Liu, Liu et al. (2016) presented asimulation model for deep-water horizontal well with diesel-based
drilling fluid, considering the effects of gas kick. What’s more, many
researchers had focused on the temperature profile when it’s inproduction stage (Yoshioka, Zhu et al. 2005, Li and Zhu 2010, Duru andHorne 2013), most of which are vertical wells. Sun, Gao et al. (2008)
calculated the wellbore temperature when drilling vertical wells indeepwater and predicted the hydrate formation region.
Previous studies about temperature calculation when drilling a well only

Nomenclature==INTRODUCTION

KEY WORDS: deepwater drilling; horizontal well; wellbore
temperature; hydrate formed region; openhole

𝑄𝑝 , 𝑄𝑎

𝑐𝑚 , 𝑐𝑒604