Study on Distribution of Wellbore Temperature in Gas Drilling with Gradient Equations

Abstract

Precise calculation of gas temperature profile is the key to gas drilling design. It is traditionally assumed that the gas temperature distribution in the wellbore is equal to the formation temperature, without considering the influence of fluid flow and Joule-Thomson cooling effect. This paper puts forward a gradient equation method for gas temperature distribution in wellbore considering gas flow and Joule-Thomson local cooling of the bit. The method applies pressure, temperature, density, and velocity equations to gas flow in drillstrings and annulus. The solution of the gradient equation is in the form of the fourth-order Runge-Kutta equation. Bottom wellbore temperatures measured at depths of 700 to 2000 m in an actual well are consistent with those predicted by the gradient method. Due to the Joule-Thomson cooling effect at the bit nozzle, the temperature drops by about 30°C. The sensitivity analysis is carried out by gradient method, and the results show that the temperature drop range of different nozzle sizes can reach 60°C due to the Joule-Thomson cooling effect. Stable temperature curves can be established within a few minutes of the gas cycle. Due to the influence of gas flow and Joule-Thomson cooling, the gas temperature in the wellbore deviates significantly from the geothermal temperature in the formation under the flow condition. The temperature of the gas in drillstrings increases as the drill depth increases and then decreases rapidly near the bottom of the hole. As the gas flows upward along the annulus, the gas temperature rises first, surpasses the formation temperature, and then decreases gradually along the geothermal gradient trend.

Solution and Analysis of Wellbore Temperature and Pressure Field Coupling Model under Lost Circulation

“…Although the research on wellbore heat transfer of drilling fluid under no-loss circulation conditions has become mature, there are few studies on variable mass heat transfer of annulus fluid under loss circulation. − In 2017, Chen et al established the first variable mass heat transfer model in the wellbore under the lost circulation condition and also proposed a method to judge the position of the loss zone according to the temperature gradient curve. However, due to its failure to fully consider the heat source generated in the drilling process and the influence of the casing program on the wellbore temperature distribution, the model has a large error in the drilling process of deep and ultradeep wells.…”