Low-Frequency DAS for Well Interval Productivity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Optimizing the performance of horizontal wells stimulated via hydraulic fracturing requires determining the relative contributions of each fracture stage to total oil production, which is challenging without this information, making it difficult to assess well treatment strategies during completion or after production has commenced.
Innovation Solution
The method utilizes low-frequency Distributed Acoustic Sensing (DAS) to monitor oil flow rates along hydrocarbon reservoirs by analyzing transient temperature changes and fluid flow velocities, allowing for the inference of relative productivity of well intervals through the interpretation of DAS signals and thermal expansion measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high frequency DAS signals are used for monitoring, then hydraulic fracture detection and injection fluid allocation can be achieved, but fluid flow rate measurement and temperature change detection are insufficient
Solution Approach 1:
The patent applies parameter changes by transitioning from high frequency DAS signal analysis to low frequency DAS signal analysis. This parameter change enables the system to detect temperature changes and measure fluid flow rates, which were not detectable using high frequency signals alone. The low frequency band captures thermal expansion and contraction effects that manifest as slow-varying strain signals, thereby resolving the contradiction between flow rate measurement precision and temperature information retention.
2Measurement precision
If traditional acoustic stimuli and Doppler shifts are used, then fluid flow can be detected, but the system complexity and equipment requirements increase
Solution Approach 1:
The patent replaces traditional mechanical acoustic stimuli and Doppler shift equipment with a simplified optical fiber-based DAS system. Instead of using external acoustic sources or complex Doppler measurement equipment, the invention utilizes low frequency DAS signals that naturally capture fluid flow-induced thermal expansion and contraction. This substitution dramatically reduces equipment complexity while maintaining fluid flow detection precision.
3Productivity
If relative productivity of well intervals is determined, then hydraulic fracturing program optimization is enabled, but the measurement and interpretation difficulty increases
Solution Approach 1:
The patent introduces thermal expansion and contraction as an intermediary mechanism to indirectly measure fluid flow rates and determine relative productivity of well intervals. Instead of directly measuring productivity, which is difficult, the system measures temperature-induced dimensional changes in the optical fiber that correlate with fluid flow. This intermediary approach simplifies the measurement process while enabling hydraulic fracturing program optimization through relative productivity determination.
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 approach enables accurate monitoring of fluid flow rates and productivity of well intervals, providing insights into reservoir performance and fracture characteristics, thereby optimizing hydraulic fracturing programs and production planning.
Implementation Method 1
DAS is the measure of Rayleigh scatter distributed along the fiber optic cable. A coherent laser pulse is sent along the optic fiber, and scattering sites within the fiber cause the fiber to act as a distributed interferometer
Implementation Method 2
The intensity of the reflected light is measured as a function of time after transmission of the laser pulse. Changes in the reflected intensity of successive pulses from the same region of fiber are caused by changes in the optical path length of that section of fiber
Implementation Method 3
The method utilizes low-frequency Distributed Acoustic Sensing (DAS) to monitor oil flow rates along hydrocarbon reservoirs by analyzing transient temperature changes and fluid flow velocities, allowing for the inference of relative productivity of well intervals through the interpretation of DAS signals and thermal expansion measurements
Data Source
Figure 1~2
Figure 3~4
AI summary
A system and method for monitoring oil flow rates along a producing oil or gas well using a Distributed Acoustic Sensing fiber is described. This system uses the low-frequency component of the acoustic signal as a measurement of temperature variations within the well. The relative flow contributions can then be inferred from these temperature fluctuations.