Milling System Eccentric Pockets Casing Windows
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Solution Overview
Problem
The existing method of plugging and abandoning wellbores using cement plugs often results in unsatisfactory seals due to leakage through voids and cracks in the cement, particularly when there are two adjacent casing strings, leading to potential contamination of surface environments and sensitive formations.
Innovation Solution
A milling system comprising a bottomhole assembly (BHA) with a window mill, section mill, and stabilizer, which includes tubular housings with eccentrically arranged pockets and movable arms equipped with cutters, allows for radial cutting and longitudinal milling of casing strings to create windows and sections, providing a more secure seal by stabilizing the milling process and preventing fluid leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cement plugs are used to plug and abandon wellbores, then the wellbore can be sealed from the environment, but fluid leakage through voids and cracks in the cement occurs leading to unsatisfactory seals
Solution Approach 1:
The invention divides the sealing task into multiple segments by creating separate windows in different casing strings (inner casing and outer casing) rather than relying on a single cement plug. This segmentation allows for controlled access points while maintaining overall seal integrity, preventing fluid leakage paths that would occur through continuous cement plugs with voids and cracks.
Solution Approach 2:
The invention extracts and removes sections of casing strings (creating windows) rather than attempting to seal around them with cement. This extraction approach eliminates the need for cement to bridge across casing interfaces, which is where voids and cracks typically form, thereby preventing fluid leakage at these critical locations.
2Ease of manufacture
If cement plugs are used to seal the wellbore, then the procedure can be performed with existing equipment, but the cement develops voids and cracks that allow fluid leakage
Solution Approach 1:
The invention replaces the chemical/mechanical cementing process with a mechanical milling process. Instead of pumping cement into the annulus and relying on it to seal, the system uses a milling tool with cutters to physically remove casing material and create precise windows. This substitution eliminates the inherent imprecision of cement placement and curing, achieving superior seal quality through controlled mechanical removal of material.
3Reliability
If a milling system with movable arms and cutters is used to create windows in casing strings, then secure seals can be formed, but the device complexity increases
Solution Approach 1:
The milling system employs dynamically adjustable movable arms that can extend and retract, allowing the fixed housing to adapt to different casing inner diameters. This dynamic capability enables a single device design to handle multiple casing sizes without requiring multiple fixed-size tools, managing the complexity through controlled movement rather than multiple static configurations.
Solution Approach 2:
The milling system nests multiple functional components within a tubular housing structure. The movable arms with cutters are contained within the housing, which itself is deployed through existing casing strings. This nesting approach consolidates complex functionality into a compact deployable unit that can be inserted through narrow annuli while maintaining reliable sealing capability.
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 milling system effectively forms secure windows and sections in the casing strings, enhancing the sealing capability and preventing fluid leakage, thereby ensuring a reliable plugging and abandonment of wellbores without contaminating surface environments or sensitive formations.
Implementation Method 1
Each arm has a body portion and a blade portion extending from an outer surface of the body portion. The mill includes cutters disposed along each blade portion... radially cutting and longitudinal milling of casing strings
Implementation Method 2
The mill includes an actuator for extending the arms... hydraulic actuator for extending the arms
Implementation Method 3
The stabilizer further comprises a pad disposed along an outer surface of each arm... stabilizing the milling process
Data Source
AI summary
A mill for use in a wellbore includes a tubular housing having a bore therethrough and a plurality of eccentrically arranged pockets formed in a wall thereof and an arm disposed in each pocket. Each arm has a body portion and a blade portion extending from an outer surface of the body portion and is movable between an extended position and a retracted position. The mill further includes cutters disposed along each blade portion and a block disposed in each pocket and connected to the housing. Each block has a guide engaged with a mating guide of the respective body portion and an inner passage for providing fluid communication between the housing bore and the respective pocket. The mill further includes an actuator for extending the arms.