Ultrasonic Acoustic Logging for Weak Interfacial Layers
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Solution Overview
Problem
Current well logging methods are inadequate for accurately measuring the mechanical properties of tight hydrocarbon-bearing formations, particularly in laminated shale/siltstone and sand/carbonate formations, as they fail to detect thin layers of weakness that can affect hydraulic fracturing due to limitations in resolution and the inability to assess in-situ conditions.
Innovation Solution
The use of high-resolution ultrasonic pitch-catch and pulse-echo measurements in boreholes to determine slowness indications and borehole radius, allowing for the identification of potential planes of weakness by analyzing the mechanical strength and compliance of formation layers, which can be used to optimize hydraulic fracturing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional sonic tools with signal frequency at most 20 kHz are used, then measurements can be conducted over large areas, but the resolution is insufficient to detect thin layers of weakness
Solution Approach 1:
The patent applies dynamic sampling along the borehole with the ultrasonic tool, taking multiple measurements at different positions. By moving the tool and collecting data points sequentially along the borehole length, high-resolution vertical profiling is achieved while maintaining comprehensive coverage of the formation area.
Solution Approach 2:
The patent transitions from conventional single-point or limited-aperture measurements to high-resolution ultrasonic measurements that resolve layers in the vertical dimension (along the borehole). This dimensional resolution allows detection of thin horizontal layers that were previously averaged out, while the horizontal coverage is maintained through tool movement.
2Length of stationary object
If conventional sonic measurements averaging over several feet are used, then measurement depth is achieved, but thin layers of weakness are not detected
Solution Approach 1:
The patent segments the formation into thin discrete layers by using ultrasonic measurements with sufficient resolution to distinguish individual layers. Instead of averaging over thick intervals, the measurement system divides the formation into resolvable stratigraphic units, allowing detection of thin incompetent layers between competent layers.
Solution Approach 2:
The patent uses dynamic sampling along the borehole length, moving the ultrasonic tool to collect measurements at multiple depth positions. This dynamic approach enables deep coverage while maintaining high vertical resolution, as each position provides detailed layer information without averaging over large depth intervals.
3Measurement precision
If laboratory measurements on cores are used, then detailed rock properties are obtained, but the rock conditions are altered from in-situ state
Solution Approach 1:
The patent creates an in-situ copy of the formation conditions by performing ultrasonic measurements directly in the borehole. This copying approach captures the mechanical properties of the formation layers while they remain in their original stressed state, avoiding the alterations that occur during core retrieval and laboratory testing.
Solution Approach 2:
The patent uses the borehole as an intermediary medium to access and measure the formation in-situ. The ultrasonic tool transmits measurements through the borehole environment to the formation layers, enabling detailed property assessment without physical removal of the rock, thus preserving in-situ conditions.
4Measurement precision
If high-resolution ultrasonic measurements are used, then thin layers of weakness are detected, but measurement complexity increases
Solution Approach 1:
The patent replaces complex mechanical core sampling and laboratory testing systems with an in-situ ultrasonic measurement system. This substitution achieves high-resolution layer detection without the complexity of core retrieval, handling, and laboratory analysis, while maintaining formation integrity and in-situ conditions.
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 provides detailed, high-resolution data on the mechanical properties of formation layers, enabling the detection of thin, weak layers that can arrest hydraulic fracture growth, thereby improving the design and prediction of hydraulic fracturing processes.
Implementation Method 1
operating an ultrasonic acoustic logging tool in the borehole to generate pitch-catch measurements along a length of the borehole
Implementation Method 2
Slowness indications (e.g., slowness values and/or wavespeed values) of the formation along the length of the borehole are determined using the pitch-catch measurements
Implementation Method 3
The borehole radius along the length of the borehole is determined using the ultrasonic pulse-echo measurements
Data Source
AI summary
Methods utilizing ultrasonic acoustic logging tools are provided for detecting thin formation layers that present markedly higher compliance than that of the surrounding rock in, for example, a laminated tight hydrocarbon-bearing formation. These layers may be interpreted as presenting potential interfacial and planes of weakness that may have bearing on the extent of a hydraulic fracture propagating across them.