DAS VSP Fracture Height and Density Extraction
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Solution Overview
Problem
Current methods for assessing induced fracture properties during hydraulic fracturing operations in subterranean formations are limited in accurately determining fracture height and density, which affects hydrocarbon production rates and optimal fracturing parameter settings.
Innovation Solution
The DAS VSP technique uses distributed acoustic sensing with optical fibers to measure seismic waves before and after fracturing, applying forward modeling and inversion schemes to calculate theoretical acoustic wave travel time differences, thereby determining induced fracture height and density, and optimizing hydraulic fracturing parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional seismic survey methods are used to assess fracture properties, then the measurement process is simpler, but the accuracy of fracture height and density determination is insufficient
Solution Approach 1:
The patent introduces an optical fiber as an intermediary element within the wellbore to detect acoustic waves. The fiber acts as a distributed sensor that converts mechanical wave energy into optical signal changes, enabling precise measurement of fracture properties without requiring complex external measurement equipment. This intermediary approach resolves the contradiction by providing high measurement precision through the fiber's intrinsic sensing capability while keeping the overall system relatively simple.
Solution Approach 2:
The patent replaces traditional mechanical seismic sensors with an optical-based detection system. By using distributed acoustic sensing through optical fibers, the system substitutes mechanical measurement apparatus with an optical field-based approach, achieving higher measurement precision for fracture characterization while reducing the complexity of mechanical sensor arrays and their associated processing equipment.
2Productivity
If hydraulic fracturing parameters are not optimized, then the operation is simpler to perform, but hydrocarbon production rates are reduced
Solution Approach 1:
The patent implements a feedback mechanism where real-time acoustic data collected during hydraulic fracturing operations is continuously analyzed to assess fracture propagation characteristics. This feedback information is then used to dynamically adjust fracturing parameters such as injection rate and pressure, enabling optimization of hydrocarbon production while maintaining a relatively simple operational framework through data-driven decision making.
Solution Approach 2:
The patent performs preliminary acoustic measurements and forward modeling before actual fracturing operations to predict fracture behavior and pre-determine optimal parameters. By conducting these preparatory actions in advance, the system enables optimized hydrocarbon production without requiring complex real-time adjustments during the fracturing process itself.
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 allows for precise determination of fracture characteristics, enabling the optimization of hydraulic fracturing parameters, such as treatment volume and injection rate, to enhance hydrocarbon production and improve well performance.
Implementation Method 1
Distributed acoustic sensing (DAS) may be used to acquire the seismic data to form the VSP. Acoustic sensing based on DAS uses the Rayleigh backscatter property of a fiber's optical core to spatially detect disturbances that are distributed along a length of fiber positioned within a wellbore.
Implementation Method 2
Seismic waves entering the region with vertical fractures often exhibit seismic anisotropy characteristics. Seismic anisotropy is the dependence of seismic propagation velocity on direction or upon angle. Rocks with vertically aligned fractures are classified and modeled as an HTI (Horizontal Transversely Isotropic) medium with a horizontal TI (transverse isotropy) symmetry axis.
Implementation Method 3
Hydraulic fracturing in a horizontal well generates vertical induced fractures in the rock around the treated region filled with hydraulic fracturing fluid, wherein the fracturing fluid decreases the velocity of the acoustic wave entering in and delays its arrival at the well.
Data Source
AI summary
A DAS VSP technique is used to determine the induced fracture height and fracture density of an induced fracture region. The DAS VSP technique obtains pre-hydraulic fracturing DAS VSP survey time-lapse data to establish a baseline reference for the direct acoustic wave travel time. The DAS VSP technique obtains one or more time-lapse data corresponding to the subsequent monitor surveys conducted after each hydraulic fracturing stage along the well. Forward modeling is used to determine a theoretical acoustic wave travel time difference. The forward modeling uses seismic anisotropy to describe the behavior of seismic waves traveling through the induced fracture regions. An inversion scheme is then used to invert for the induced fracture height and the fracture density using the forward modeling. The two extracted induced fracture characteristics may then be used to determine optimal hydraulic fracturing parameters.