Tapered Cavern Geometry for Wellbore Stress Distribution
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Solution Overview
Problem
Existing methods for improving resistance of well bottom zones to yield loads during oil and gas production and underground gas storage operations are inadequate, as they either reduce well output, increase equipment wear, or lead to stress concentration zones that fail under changing formation pressures.
Innovation Solution
A method involving the jet-breaking of a tapered cavern within the well bottom zone before casing installation, with specific parameters (Rc−R−δ≥4 cm and 5°≤α≤30°) and subsequent cementation, which reduces shear stress concentrations and enhances the well's resistance to yield loads by distributing compression loads at an angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sand screens are installed to prevent sand withdrawal, then sand control is improved, but well output is reduced due to filtration resistance
Solution Approach 1:
The well bottom zone is segmented into distinct functional zones: a tapered cavern zone for stress distribution, a cementation zone for structural support, and a screened zone for sand control. This segmentation allows each zone to perform its specific function optimally without interfering with others, maintaining well output while providing effective sand control.
Solution Approach 2:
The tapered cavern is created and cemented before installing the sand screen. This preliminary action prepares the well bottom zone to distribute stresses and support the screen structure, preventing screen failure and maintaining productivity throughout the well's operational life.
2Reliability
If well flow rate is reduced to counter sand withdrawal, then sand control is improved, but well deliverability is reduced
Solution Approach 1:
A tapered cavern with curved generatrix is created instead of a cylindrical hole. The curved geometry distributes stresses more uniformly around the wellbore, preventing stress concentration that would lead to rock decay and sand withdrawal, thereby maintaining well deliverability without requiring flow rate reduction.
3Reliability
If reamers are used to ream the well bottom zone and cement the cavern, then sand control is improved, but stress concentration zones form that fail under pressure changes
Solution Approach 1:
An asymmetric tapered cavern geometry is used instead of a symmetric cylindrical shape. The taper angle (5°-30°) creates an asymmetric stress distribution that directs stresses away from the cavern edge into the surrounding rock formation, preventing stress concentration and improving resistance to pressure changes.
Solution Approach 2:
The cavern geometry parameters are specifically optimized: taper angle between 5°-30°, and radius relationship Rc−R−δ≥4 cm. These parameter changes ensure that stresses are properly distributed and that the cavern provides adequate support without creating failure zones.
4Ease of manufacture
If conventional cementation is performed without a tapered cavern, then installation is simple, but shear stress concentrations develop on the casing wall
Solution Approach 1:
The tapered cavern is created and cemented before installing the production casing. This preliminary action prepares the well bottom zone to distribute shear stresses, preventing stress concentrations on the casing wall during subsequent operations and extending casing life.
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 method significantly reduces shear stress peak values and improves the well's resistance to yield loads, minimizing the amount of decayed rock particles entering the well bore and reducing the risk of equipment failure and water cut in extracted fluids.
Implementation Method 1
within the zone of contact of producing formation with the impermeable top thereof a tapered cavern having a top directed towards the formation inner part is jet-broken
Data Source
AI summary
A method for improving the stability of reservoir rock in bottomhole zones of wells to destructive loads developing during operation of wells at oil and gas fields during operation at underground gas storages is disclosed. Prior to running of casing string in zone of contact of productive formation with its impenetrable roof it is proposed to drill or blur cone-shaped cavern with vertex facing the formation, the cavity parameters must satisfy the conditions according to the depth of the cavity counted from the well wall along the contact line of the productive formation and its impermeable roof should exceed 4 cm, and the angle between the cone generatrix and the casing pipe generatrix within the range of values from 5° up to 30°. This will increase well bottomhole zone stability to destructive loads developing in process of its operation and reduction of volumes of broken rock carried to well bore.