Optimization of Single-Trip Milling Using Large-Diameter Coiled Tubing

Topics: Coiled tubing Directional/extended reach wells

Larger-diameter coiled tubing (CT) recently has been used to perform millouts because of its improved set-down force and increased annular velocities (AVs) for cleanout purposes. Service companies and operators have reduced the number of wiper trips when using larger-diameter CT, to save time and money. Milling efficiency using 2-in. CT can be dramatically improved by maintaining proper fluid rheology throughout the operation. By doing so, 2-in. CT has been used to perform single-trip millouts, reducing operational time by 40%.


The main objective of CT operations in horizontal wells is to clean the lateral completely of any debris without compromising the well’s integrity. The first and most important component of single-trip-millout operations is correct fluid rheology. This system comprises the AV, Reynolds number (RE), and fluid viscosity. With correct use of chemicals and proper AVs, the fluid system allows sand and debris to travel out of the wellbore.

The RE determines the flow regime as laminar, transitional, or turbulent. Turbulent flow is characterized by swirling of the water (i.e., presence of eddies), which agitates the settling bed, enabling sand and debris to flow out of the lateral and, in turn, out of the well. RE can be broken into three components: fluid velocity, hydraulic diameter (flow area between casing and coil), and kinematic viscosity (funnel viscosity). In this case, the hydraulic diameter is predetermined by the 2-in. CT working in 7- to 4.5-in. cased wells, leaving the velocity and viscosity dependent on each operation.

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 179090, “Optimization of Single-Trip Milling Using 2-in. Coiled Tubing,” byElizabeth Snyder, SPE, and Justin Noland, SPE, Sanjel, prepared for the 2016 SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, Houston, 22–23 March. The paper has not been peer reviewed.
This article is reserved for SPE members and JPT subscribers.
If you would like to continue reading,
please Sign In, JOIN SPE or Subscribe to JPT

Optimization of Single-Trip Milling Using Large-Diameter Coiled Tubing

01 June 2016

Volume: 68 | Issue: 6