Downhole Pump Half-Stroking Detection via Pressure Differential Monitoring
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Solution Overview
Problem
Downhole pumps used for formation fluid sampling can experience half-stroking, leading to impaired fluid draw and inaccurate volume calculations, which affects the efficiency and accuracy of formation evaluation and fluid contamination predictions.
Innovation Solution
Monitoring pressure differentials between formation pressure and fluid pressure within the downhole tool, comparing these differentials for consecutive strokes to identify the onset of half-stroking, and adjusting volume calculations accordingly to account for this anomaly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pump half-stroking is not detected, then fluid volume calculations remain simple, but the accuracy of formation evaluation and contamination predictions deteriorates
Solution Approach 1:
The system continuously monitors pressure differentials during pump strokes and uses this feedback to detect half-stroking conditions. The controller compares actual pressure differentials with expected values and adjusts volume calculations in real-time based on detected anomalies, ensuring accurate formation evaluation while maintaining a relatively simple system architecture
Solution Approach 2:
The patent replaces complex mechanical flow measurement systems with a pressure-based detection method. Instead of using mechanical flow meters or complex sensors, the system uses pressure differential measurements across the pump to infer flow conditions and detect half-stroking, simplifying the measurement system while maintaining accuracy
2Reliability
If pressure differential monitoring is implemented for every stroke, then half-stroking detection accuracy improves, but the time and computational resources required increase
Solution Approach 1:
The system monitors pressure differentials for all strokes but applies full analysis only when anomalies are detected. During normal operation, the system uses simplified monitoring, and only performs comprehensive analysis when pressure differential patterns indicate potential half-stroking conditions, reducing overall processing time while maintaining high detection reliability
Solution Approach 2:
The system establishes expected pressure differential ranges and detection criteria before pump operation begins. By pre-defining thresholds and analysis protocols, the system avoids complex real-time calculations for every stroke and only performs detailed analysis when conditions warrant it, reducing computational overhead while maintaining detection accuracy
Data Source
AI summary
Various methods for detecting and accounting for the effects of half-stroking by a pump are provided. In one embodiment, a method includes operating a pump of a downhole tool to pump fluid from a formation through the downhole tool and determining pressure differentials between a formation pressure and pressure of the fluid within the downhole tool. The pressure differentials for each of a forward stroke and reverse stroke of the pump can be summed and then compared to enable identification of onset of half-stroking by the pump. Additional systems, devices, and methods are also disclosed.