Underbalanced Coiled Tubing Drilling in Tight Sandstone Case Study: Part Two
Author: Guest Blog by Naceredine Fares
Published: 23rd January 2019
In a recent blog post we looked at how Underbalanced Coiled Tubing Drilling (UBCTD) has the potential to offer a more than viable method of extraction from tight sandstone formations.
To recap, the results of the project we presented in the post were impressive. The production recorded on the preliminary post well flow test showed a production of three times the target flow. (A summary of this UBCTD project can be found here.)
What is particularly interesting to note is that the project did not run smoothly and resulted in unexpected additional costs. But despite these challenges and costs, UBCTD still remained an impressively viable option.
Overall the project faced excessive tripping time. It took over 30 runs (including two whipstocks and four milling runs) to drill approximately 2,400 ft.
Achieving the run in hole was difficult because it involved drilling through an unstable clay-stone formation. However, the accuracy enabled by the UBCTD approach meant drilling could be controlled successfully and enough reservoir contact could be achieved.
The second whipstock needed to be installed to reduce the dog leg severity and make it easier to trip in. Again, the accuracy of the UBCTD approach enabled the second whipstock to be situated next to the first.
The project saw three laterals being drilled. All three had their total depth called earlier than planned because of drilling difficulties. An impressive flow rate was still achieved in spite of this.
The high stage separator saw excessive foam, meaning antifoam had to be injected upstream at the 5k choke.
At first glance, it would be easy to assume that drilling using UBCTD in tight sandstone was only economically viable in this instance because the project ran unusually smoothly. But as these insights show, the project was far from seamless. It illustrates that UBCTD is a method that delivers in the real world.