Outer Casing Window Milling With Stabilizer for Wellbore Sealing
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Solution Overview
Problem
Existing methods for plugging and abandoning wellbores with multiple casing strings often result in unsatisfactory seals due to leaks through voids and cracks in the cement, leading to potential contamination of surface environments and sensitive formations.
Innovation Solution
A method involving a bottom hole assembly (BHA) with a radial cutout and window mill (RCW) and section mill to form an outer window in the outer casing string, utilizing hydraulic actuators to extend cutting arms for precise milling and stabilization, ensuring effective sealing by forming a controlled window in the inner and outer casings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cement plugs are used to seal the wellbore with multiple casing strings, then the wellbore is sealed from the environment, but leaks occur through voids and cracks in the cement causing contamination
Solution Approach 1:
The wellbore is divided into multiple isolated sections using cement plugs placed at different depths. Each casing string creates a separate barrier, and cement plugs seal specific intervals between casing strings and the formation, preventing continuous fluid migration paths and isolating contamination sources.
Solution Approach 2:
Cement acts as an intermediary material filling the annular space between casing strings and the wellbore formation. The cement plug serves as a mediating seal that bridges the gap between the metal casing and the rock formation, creating a continuous barrier that prevents fluid leakage through the interface.
2Ease of manufacture
If conventional cementing procedures are used for plugging and abandonment, then the process is simple and cost-effective, but the seal is unsatisfactory due to voids and cracks
Solution Approach 1:
The wellbore is prepared in advance by running multiple casing strings to designated depths and cementing them in place before the final plugging operation. This preliminary casing and cementing creates a structured framework that guides the subsequent cement plug placement and ensures proper sealing zones are established before abandonment.
Solution Approach 2:
The cementing process parameters are modified by placing cement plugs at specific intervals between casing strings rather than a single continuous cement job. The cement composition and placement pressure are optimized for each annular space to ensure complete filling and elimination of voids, improving seal integrity while maintaining procedural simplicity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method provides a robust and controlled means to form windows in casings, enhancing the sealing process, thereby preventing wellbore fluid leakage and ensuring the integrity of the wellbore seal during plugging and abandonment.
Implementation Method 1
A method involving a bottom hole assembly (BHA) with a radial cutout and window mill (RCW) and section mill to form an outer window in the outer casing string, utilizing hydraulic actuators to extend cutting arms for precise milling
Implementation Method 2
utilizing hydraulic actuators to extend cutting arms for precise milling and stabilization
Data Source
Figure 1A
Figure 1B~1C
Figure 2A~2C
AI summary
A method of milling an outer casing in a wellbore comprises deploying a bottom hole assembly (BHA) into the wellbore through an inner casing string, the BHA comprising a first mill and a stabilizer located below the first mill, the first mill and the stabilizer each comprising a tubular housing having an upper end, a lower end, and a bore extending continuously from the upper end to the lower end. The method further comprises extending arms of the stabilizer through a window or milled section of the inner casing string and into engagement with an inner surface of an outer casing string, extending arms of the first mill through the window or milled section and radially cutting through the outer casing string, thereby forming an outer window through the outer casing string, and longitudinally advancing the BHA while longitudinally milling the outer casing string using the first mill, thereby opening the outer window. The BHA can be retrieved from the wellbore and through the inner casing.