Session: 11-02-02-Well Drilling Fluids and Hydraulics-2

Paper Number: 104713

104713 - Application of Insulated Drill Pipe to Supercritical/super-Hot Geothermal Well Drilling 

In Japan, a research and development project are ongoing that is aimed at developing supercritical geothermal exploration and power generation methods. The extremely high formation temperatures encountered during supercritical geothermal drilling presents a challenge for the durability of downhole tools. Thus, it is essential to design an effective method of downhole cooling during drilling. In this study, the authors carried out numerical simulations focusing on the effectiveness of using insulated drill pipes to reduce downhole temperatures during drilling fluid circulation. The objective is to reduce the downhole temperature in supercritical geothermal wells to below 175°C that coincides with the lowest heat resistant temperature of most downhole tools.

　Conventional drill pipes are made of carbon steel. The insulated drill pipes, considered here, have a structure similar to conventional drill pipes, but include additional thermally insulating material. The insulation material is placed inside the pipe body and covered by an inner liner tube. The formation temperature and drilling conditions for the simulations were based on the Kakkonda WD-1a research well in Japan. The well has a depth of 4000 m and a maximum formation temperature of over 600°C. In the simulation study, the authors used a modified downhole temperature simulation program “GEOTEMP2,” which was originally developed by Sandia National Laboratories.

　It was found that use of insulated drill pipes effectively controlled the downhole temperature by reducing the heat influx conducted from the formation. Considering the additional cost of using insulated drill pipes, we also looked at cases where the insulated drill pipes were only applied along the 2/3 parts of the entire drillstring. It was most effective to apply insulated drill pipes along the shallow sections of the string. Considering the flow rate of the circulating fluid and the inflow temperature, the temperature simulation was performed to keep the downhole temperature below 175°C.

　Another issue to be considered is that the inner diameter of insulated drillpipe is smaller than conventional drillpipe, which is disadvantage of the use of insulated drill pipe because of the increase in frictional pressure loss. According to the calculation of friction pressure loss for a turbulent flow in circular pipe, when insulated drill pipe was applied at the entire depth, the pressure loss will be 4.8 times higher than conventional one. When insulated drill pipe was applied to the 2/3 parts of the entire drillstring, pressure loss will be 3.6 times higher than conventional one. If insulated drill pipe is used, it is necessary to select an appropriate mud pump based on the result of frictional pressure loss calculation.

Presenting Author: Ajima Kohei Akita University

Presenting Author Biography: Mr. Kohei Ajima is currently a first-year Master’s course student in the Graduate School of International Resource Sciences at Akita University, Japan under the supervision of Professor Shigemi Naganawa. His research interests include thermal-hydraulics simulation in extremely high temperature well drilling. He received his B.S. degree in Resource Science and Engineering from Akita University.

Authors:

Ajima Kohei Akita University
Shigemi Naganawa Akita University
Elvar Karl Bjarkason Akita University