Case Study of Section Milling Field Run Leads to Technology Design Optimization Using Advanced Numerical Simulations and Modeling

Abstract

In recent years, plug and abandonment (P&A) technologies have been receiving greater global attention as more and more fields reach the end of their productive life. The objective of permanent P&A is permanent isolation. Several operators have requested the development of a section mill capable of milling two adjacent casing strings. Removing two adjacent casing strings enables a permanent, solid-cement "rock-to-rock" barrier across the formation in open hole. Various methods have been used to section mill dual casing strings with results ranging from costly multiple trips to total failures. The scope of the project was to develop a milling system that permits the removal of both 9 5/8-in. and 13 3/8-in. (or 13 5/8-in.) casing in either one trip or multiple trips into and out of the well. The new milling system should be capable of handling different flow rates for successful tool operation and efficient hole cleaning. The focus of the new milling system also was to minimize trips and bottomhole assembly handling to reduce operational cost. The new technology enables the removal of more than 100-ft (30-m) section of inner and outer casings in multiple trips. In this work, we conducted extensive numerical simulations using computational fluid dynamics to achieve the best possible milling system configuration.