Downhole Probe Anchor Point for Relative Depth Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for determining the absolute depth of downhole measurements in wellbores are prone to errors due to distortions in wireline length measurements, leading to uncertainties in fluid density and gradient calculations, making it difficult to accurately detect density changes between different depths.
Innovation Solution
A downhole probe equipped with a detachable anchor and tether unit that allows for accurate measurement of relative distances between measurement locations by deploying a tether between the anchor and the measurement unit, providing a more reliable indication of separation distance than surface-based measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If surface-based wireline length measurement is used to determine absolute depth, then the measurement system is simple and easy to operate, but the measurement precision deteriorates due to cumulative distortions resulting in ±2 feet uncertainty per 1000 feet
Solution Approach 1:
The measurement system is segmented into multiple sections: a fixed anchor point secured in the wellbore, a movable probe, and a tether connecting them. The total depth measurement is segmented into the known anchor depth plus the measured tether length, breaking the cumulative error problem into discrete, measurable segments that can be independently calibrated and measured with higher precision.
Solution Approach 2:
The tether acts as an intermediary measurement element between the surface equipment and the downhole probe. Instead of measuring wireline length directly from the surface (which accumulates distortion errors), the tether provides a dedicated, localized measurement path that can be precisely tracked as it pays out from the probe to the anchor point, serving as a mediator that transfers the measurement function with higher accuracy.
2Device complexity
If absolute depth measurement with ±2 feet uncertainty is used, then the measurement process is straightforward, but the reliability deteriorates for detecting small density changes in fluid gradients
Solution Approach 1:
The anchor point is preliminarily positioned and secured in the wellbore at a known depth before the actual fluid gradient measurements are taken. This preliminary action establishes a fixed reference point that eliminates the need for repeated absolute depth measurements, allowing subsequent tether length measurements to focus solely on relative position changes with higher reliability for detecting small density variations.
Solution Approach 2:
The system incorporates feedback by continuously monitoring the tether length as the probe moves relative to the fixed anchor point. This real-time feedback on relative position, combined with pressure measurements, allows for accurate calculation of fluid gradients and density changes without being affected by the cumulative errors that plague absolute depth measurement systems.
Data Source
AI summary
A downhole probe can be utilized in a wellbore to accurately determine a relative depth between measurement locations. The downhole probe includes a measurement unit for taking downhole measurements and a detachable anchor that can grip a wellbore wall to maintain a fixed location. The measurement unit may be moved relative to anchor between the measurement locations to unspool a tether coupled between the anchor and the measurement unit. The length of the tether unspooled may provide a more accurate indication of the relative distance between the measurement locations than surface-based measurements. The detachable anchor may be retrieved for deployment at additional measurement locations or may be abandoned in the wellbore.