Stress Equilibrium Detection in Core Rock Samples

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Solution Overview

Problem

Current methods for testing shaped charges before use downhole in earth or rock drilling fail to accurately determine when applied stress has equilibrated in a core rock sample, leading to uncertainties in perforation performance due to varying rock properties and compressive strengths.

Innovation Solution

A testing chamber simulates downhole conditions using an overburden chamber and a wellbore chamber, applying overburden and wellbore pressures to a core rock sample, with a pressure transducer monitoring the differential pressure between overburden and pore fluid pressures to determine when the stress has equilibrated, indicated by a stable rate of change, allowing for precise timing of shaped charge detonation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If current methods are used to test shaped charges, then testing can be performed, but the determination of stress equilibrium is inaccurate leading to uncertainties in perforation performance

Engineering Contradiction:

Improvestress equilibrium determinationVSAvoidperforation performance prediction

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The system continuously monitors pore pressure in real-time during the application of overburden stress and uses this feedback to detect when stress equilibrium has been achieved. The pore pressure response serves as an indicator that the rock matrix has fully transferred and equilibrated the applied stress, providing an accurate trigger point for shaped charge detonation.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The invention replaces traditional mechanical stress measurement methods with a pore pressure-based detection system. By monitoring fluid pressure within the rock's pore space, the system indirectly measures stress equilibrium without requiring direct mechanical sensors in the rock, enabling more precise and reliable detection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Productivity

If stress is applied quickly to the core rock sample, then testing time is reduced, but stress equilibrium may not be fully achieved leading to inaccurate results

Engineering Contradiction:

Improvetesting speedVSAvoidstress equilibration accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The system provides real-time feedback on pore pressure changes during stress application, allowing operators to monitor the approach to equilibrium continuously. This enables optimization of testing duration by stopping exactly when equilibrium is achieved rather than using fixed time intervals, balancing speed and accuracy.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

Pore fluid pressure serves as an intermediary indicator that translates the complex mechanical stress transfer process within the rock matrix into a measurable and easily monitored parameter. This intermediary measurement allows for non-intrusive, real-time monitoring of stress equilibrium without interfering with the stress application process.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of operation

If traditional timing methods are used for shaped charge detonation, then the process is simple, but the timing accuracy is insufficient due to varying rock properties and compressive strengths

Engineering Contradiction:

Improvedetonation timingVSAvoiddetonation timing accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The system allows the rock sample itself to indicate when it is ready for detonation through its pore pressure response to applied stress. The rock's own mechanical properties and stress transfer characteristics generate the signal that triggers detonation, eliminating the need for external timing calculations or estimates based on assumed rock properties.

Inventive Principle:

Principle #25Self-service

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 ensures that the shaped charge is tested under conditions representative of downhole stress equilibrium, enhancing the accuracy of perforation tunnel formation and hydrocarbon extraction by ensuring the stress has fully transferred into the core rock sample before detonation.

Implementation Method 1

A differential pressure transducer is used to determine a difference between an overburden fluid pressure and a pore fluid pressure

Methodology Applied

Scientific EffectDifferential pressure measurement: Pressure Gradient

Implementation Method 2

As the overburden stress is applied and the rock compresses, the pore fluid in the core rock sample is forced out of the core rock sample

Methodology Applied

Scientific EffectCompression: Compression

Data Source

PatentUS11604126B2Determining when applied stress to a core rock sample has equilibrated in the core rock sample

Publication Date: 2023.03.14 HALLIBURTON ENERGY SERVICES INC

AI summary

Overburden stress is applied to a core rock sample in a sleeve. Pressure is applied to pores in the core rock sample. An overburden fluid pressure indicative of the overburden stress and pore fluid pressure indicative of the pore pressure is measured. A difference between the overburden fluid pressure and pore fluid pressure is determined. The measuring and determination of the difference is repeated over a period of time. A rate of change of the difference over the period of time is determined. An indication of the rate of change meeting a threshold level is output indicative of the overburden stress transferring into and throughout the core rock sample.