Acid Etching for Fracture Orientation Control
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Solution Overview
Problem
Current methods for multistage fracturing in unconventional wellbores, such as those in carbonate and shale formations, face challenges in controlling fracture orientation and reducing breakdown pressure, which are essential for efficient hydrocarbon extraction.
Innovation Solution
Introducing an aqueous acid composition with a pH between 2 and 5, containing an acid and/or acidified chelating agent, into wellbores at etching locations to reduce formation density and direct fracturing, followed by rinsing and injecting a fracturing fluid to create fractures aligned with wormholes, thereby reducing breakdown pressure and enhancing fracture conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional multistage fracturing methods (plug and perf, ball and sleeve, pinpoint) are used, then fractures can be created in the formation, but the location and orientation of fractures are not well controlled
Solution Approach 1:
The acid etching process is performed before fracturing to pre-create wormholes and modify the formation structure at desired locations. This preliminary action enables subsequent fractures to initiate at specific, predetermined positions and orientations rather than randomly around packers, directly solving the fracture control problem without requiring complex additional equipment
Solution Approach 2:
Acid is injected at specific etching locations to create localized wormholes and modify formation properties only in targeted zones. This local modification allows precise control of where fractures will initiate and propagate, enabling independent control of fracture location and orientation at each etching site while leaving the rest of the formation unchanged
2Manufacturing precision
If acid etching is performed before fracturing, then fracture orientation control and breakdown pressure reduction are improved, but the treatment process becomes more complex
Solution Approach 1:
The acid etching process and fracturing operation are merged into a coordinated two-step sequence within the same wellbore treatment. The acid injection uses existing wellbore access points and the same fracturing equipment is used for both steps, combining multiple functions into a unified treatment workflow rather than requiring separate equipment systems
Solution Approach 2:
The acid concentration, pH level (maintained between 2-5), and injection parameters are optimized to achieve effective wormhole creation and density reduction without excessive complexity. By controlling these chemical parameters within specific ranges, the process achieves reliable fracture orientation control and breakdown pressure reduction while maintaining operational simplicity
3Manufacturing precision
If stage spacing is reduced to ensure no zone is left unstimulated, then coverage is improved, but more stages are required increasing time and cost
Solution Approach 1:
Acid etching creates pre-formed wormholes and modifies formation density before fracturing, which enables fractures to propagate more efficiently and cover larger zones from each stage location. This preliminary preparation reduces the need for closely spaced stages while ensuring complete zone stimulation, as each fracture can effectively treat a broader area
Solution Approach 2:
Acid is injected at selectively spaced etching locations rather than continuously along the wellbore, creating localized zones of modified formation properties. This allows optimization of stage spacing by placing etching locations only where fracture initiation is needed, improving coverage efficiency without requiring excessive numbers of stages
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
This approach effectively reduces breakdown pressure by up to 90% and directs fracturing within ±15° of the radial axis, improving fracture geometry and conductivity, thus enhancing hydrocarbon extraction efficiency.
Implementation Method 1
introducing an aqueous acid composition comprising an acid and/or an acidified chelating agent and having a pH in a range of from 2 to 5, into a wellbore located in a subterranean formation at one or more etching locations, which introducing reduces a density of the subterranean formation at the etching locations
Implementation Method 2
creating etched portions directionally aligned with wormholes at the etching locations
Implementation Method 3
injecting the fracturing fluid into the wellbore to thereby fracture the subterranean formation at the etching locations
Implementation Method 4
the pressure causes the shale gas-bearing formation to fracture
Data Source
AI summary
A method of controlling the fracture location, orientation, and reduce the breakdown pressure in multistage fracturing, particularly of unconventional reservoirs. Acid etching can be used to initiate small channels (wormholes) around the horizontal well, followed by the hydraulic fracturing fluid to create the fractures. The fracture orientation can follow the same direction of the etched part of the well and in the same location of the wormholes. The breakdown pressure can be reduced by 5, 10, 15%, or more, e.g., from 2200 to 1800 psi after acid etching which can minimize the pumping requirements at the surface and break the formation with very high breakdown pressure.