Registering Fiber Position to Well Depth Using Acoustic Pulses

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Solution Overview

Problem

Inaccuracies in fiber length measurements due to manufacturing inaccuracies in fiber optic cables used in wellbore depth determination, leading to ambiguities between fiber length and well depth, are not effectively addressed by conventional methods.

Innovation Solution

A downhole tool system that includes a depth detection sub-assembly, an acoustic transmitter sub-assembly, and a measurement and control sub-assembly, utilizing a fiber optic interrogator to determine the travel time of acoustic pulses along a fiber strand, allowing for accurate registration of fiber length to well depth by detecting casing collars and calculating the length of the fiber strand based on detected disturbances.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If fiber optic cables are used for wellbore depth determination, then depth measurement capability is provided, but manufacturing inaccuracies in the fiber cables cause inaccuracies in depth measurements

Engineering Contradiction:

Improvedepth measurement accuracyVSAvoidfiber cable length accuracy

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The patent replaces the mechanical/physical fiber cable length measurement system with an acoustic time-of-flight measurement system. Acoustic pulses are transmitted through the fiber optic cable, and the travel time of these pulses is measured. Since the speed of acoustic waves in the fiber is known and can be calibrated, the distance can be accurately determined by multiplying travel time by wave speed, eliminating dependence on fiber cable manufacturing length accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the measurement parameter from direct fiber length to acoustic wave travel time. By measuring the time it takes for acoustic pulses to travel through the fiber and using the known acoustic wave speed in the fiber material, the system calculates distance based on time rather than physical fiber length, thereby compensating for manufacturing variations in fiber cable length.

Inventive Principle:

Principle #35Parameter changes

2Loss of information

If conventional depth measurement methods are used, then depth information can be obtained, but ambiguities exist between fiber length and well depth

Engineering Contradiction:

Improvedepth information clarityVSAvoiddepth registration accuracy

Core Design Contradiction:

Loss of informationVSMeasurement precision

Solution Approach 1:

The patent implements a feedback mechanism where acoustic pulses are sent through the fiber optic cable and the return travel time is measured. This creates a closed-loop measurement system where the actual acoustic wave propagation time through the specific fiber installation is measured and used to calculate the precise distance, providing accurate depth registration that accounts for the actual fiber path and eliminates ambiguities between fiber length and well depth.

Inventive Principle:

Principle #23Feedback

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 system eliminates ambiguity between fiber length and well depth, enabling the fiber to serve as a permanent 'ground-truthing' sensing monitor for depth determination along the entire wellbore, providing accurate and reliable depth measurements.

Implementation Method 1

an acoustic pinger configured to generate one or more acoustic pulses

Methodology Applied

Scientific EffectAcoustic pulse generation: Acoustics

Implementation Method 2

a fiber optic interrogator communicably coupled to a fiber strand installed in the wellbore and configured to determine a travel time of the tool body along the fiber strand

Methodology Applied

Scientific EffectLight propagation in fiber optic: Optical Fibre

Data Source

PatentUS11781424B2Registering fiber position to well depth in a wellbore

Publication Date: 2023.10.10 SAUDI ARABIAN OIL CO

AI summary

A downhole tool system includes a downhole tool that includes a tool body configured to move within a wellbore, a depth detection sub-assembly and configured to generate a signal based on a known depth location of the tool body in the wellbore, an acoustic transmitter sub-assembly including an acoustic pinger configured to generate acoustic pulses, and a measurement and control sub-assembly configured to receive the signal from the depth detection sub-assembly and, based on the signal, activate the acoustic transmitter sub-assembly to initiate the acoustic pulses from the acoustic pinger. The system further includes a control system that includes a fiber optic interrogator communicably coupled to a fiber strand installed in the wellbore and configured to determine a travel time of the tool body along the fiber strand or a particular distributed acoustic sensing (DAS) channel of a plurality of DAS channels based on a detection of at least one disturbance in the fiber strand caused by the acoustic pulses.