Characterize Fracture Development Through Strain Rate Measurements by Distributed Acoustic Sensor DAS

2022 ◽  
Author(s):  
Jin Tang ◽  
Ding Zhu
Keyword(s):  
Hydraulic Fracturing ◽  
Strain Rate ◽  
Fiber Optic ◽  
Fracture Propagation ◽  
Acoustic Sensor ◽  
Observation Well ◽  
Complex Fracture ◽  
Multistage Hydraulic Fracturing ◽  
Fracture Development ◽  
Fracture Growth

Abstract In multistage hydraulic fracturing treatments, the combination of extreme large-scale pumping (high rate and volume) and the high heterogeneity of the formation (because of large contact area) normally results in complex fracture growth that cannot be simply modeled with conventional fracture models. Lack of understanding of the fracturing mechanism makes it difficult to design and optimize hydraulic fracturing treatments. Many monitoring, testing and diagnosis technologies have been applied in the field to describe hydraulic fracture development. Strain rate measured by distributed acoustic sensor (DAS) is one of the tools for fracture monitoring in complex completion scenarios. DAS measures far-field strain rate that can be of assistance for fracture characterization, cross-well fracture interference identification, and well stimulation efficiency evaluation. Many field applications have shown DAS responses on observation wells or surrounding producers when a well in the vicinity is fractured. Modeling and interpreting DAS strain rate responses can help quantitatively map fracture propagation. In this work, a methodology is developed to generate the simulated strain-rate responds to assumed fracture systems. The physical domain contains a treated well that the generate strain variation in the domain because of fracturing, and an observation well that has fiber-optic sensor installed along it to measure the strain rate responses to the fracture propagation. Instead of using a complex fracture model to forward simulate fracture propagation, this work starts from a simple 2D fracture propagation model to provide hypothetical fracture geometries in a relatively reasonable and acceptable range for both single fracture case and multiple fracture case. Displacement discontinuity method (DDM) is formulated to simulate rock deformation and strain rate responds on fiber-optic sensors. At each time step, fracture propagation is first allowed, then stress, displacement and strain field are estimated as the fracture approaches to the observation well. Afterward, the strain rate is calculated as fracture growth to generate patterns as fracture approaching. Extended simulation is conducted to monitor fracture propagation and strain rate responses. The patterns of strain rate responses can be used to recognize fracture development. Examples of strain rate responses for different fracturing conditions are presented in this paper. The relationship of injection rate distribution and strain rate responses is investigated to show the potential of using DAS measurements to diagnose multistage hydraulic fracturing treatments.

scholarly journals Hydromechanical-Coupled Cohesive Interface Simulation of Complex Fracture Network Induced by Hydrofracturing with Low-Viscosity Supercritical CO2

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 1) ◽  
Author(s):  
Xin Cai ◽  
Wei Liu
Keyword(s):  
Hydraulic Fracturing ◽  
Supercritical Co2 ◽  
Fracture Propagation ◽  
Zone Model ◽  
Hydraulic Pressure ◽  
Small Aperture ◽  
Complex Fracture ◽  
Low Viscosity ◽  
Fracturing Fluids ◽  
Low Viscosity Fluids

Abstract Hydraulic fracturing experiments with low-viscosity fluids, such as supercritical CO2, demonstrate the formation of complex fracture networks spread throughout the rocks. To study the influence of viscosity of the fracturing fluids on hydraulic fracture propagation, a hydromechanical-coupled cohesive zone model is proposed for the simulation of mechanical response of rock grains boundary separation. This simulation methodology considers the synergistic effects of unsteady flow in fracture and rock grain deformation induced by hydraulic pressure. The simulation results indicate a tendency of complex fracture propagation with more branches as the viscosity of fracturing fluids decrease, which is in accord with experimental results. The low-viscosity fluid can flow into the microfractures with extremely small aperture and create more shear failed fracture. This study confirms the possibility of effective well stimulations by hydraulic fracturing with low-viscosity fluids.

Modeling of fiber-optic strain responses to hydraulic fracturing

Geophysics ◽  
2020 ◽  
Vol 85 (6) ◽  
pp. A45-A50
Author(s):  
Zhishuai Zhang ◽  
Zijun Fang ◽  
Joe Stefani ◽  
James DiSiena ◽  
Dimitri Bevc ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Strain Rate ◽  
Fiber Optic ◽  
Low Frequency ◽  
Displacement Discontinuity ◽  
Hydraulic Fractures ◽  
Quantitative Interpretation ◽  
Current Application ◽  
Monitoring Well ◽  
And Inversion

We modeled cross-well strain/strain rate responses of fiber optic sensing, including distributed strain sensing (DSS) and low-frequency distributed acoustic sensing (DAS), to hydraulic stimulation. DSS and low-frequency DAS have been used to measure strain or the strain rate to characterize hydraulic fractures. However, the current application of DSS/DAS is limited to acquisition, processing, and qualitative interpretations. The lack of geomechanical models hinders the development of the technology toward quantitative interpretation and inversion. We have developed a strategy to use the displacement discontinuity method to model the strain field around kinematically propagating fractures. For a horizontal monitoring well, modeling results were able to explain the heart-shaped extending pattern before a fracture hit, the polarity flip due to fracture interaction during stimulation, and the V-shaped pattern when a fracture does not intersect with the monitoring well. For a vertical monitoring well, modeling shows the different characters of strain rate responses when a fracture is near and far away from a vertical monitoring well. We also investigated the effects of fractures with various geometries such as elliptic and layered fractures. We compared and verified the modeling with field data from the Hydraulic Fracturing Test Site 2, a research experiment performed in the Permian Basin. Our modeling work can be used to identify patterns in field observations. The results also help to improve acquisition design and lay the groundwork for quantitative interpretation and inversion.

Numerical Investigation of Complex Hydraulic Fracture Development in Naturally Fractured Reservoirs

2015 ◽  
Author(s):  
Wu Kan ◽  
Jon E. Olson
Keyword(s):  
Fracture Propagation ◽  
Injection Pressure ◽  
Natural Fracture ◽  
Hydraulic Fractures ◽  
Differential Stress ◽  
Complex Fracture ◽  
Fracture Patterns ◽  
Fracture Development ◽  
Fracture Complexity ◽  
Shale Reservoirs

Abstract Complex fracture networks have become more evident in shale reservoirs due to the interaction between pre-existing natural and hydraulic fractures. Accurate characterization of fracture complexity plays an important role in optimizing fracturing design, especially for shale reservoirs with high-density natural fractures. In this study, we simulated simultaneous multiple fracture propagation within a single fracturing stage using a complex hydraulic fracture development model. The model was developed to simulate complex fracture propagation by coupling rock mechanics and fluid mechanics. A simplified three-dimensional displacement discontinuity method was implemented to more accurately calculate fracture displacements and fracture-induced dynamic stress changes than our previously developed pseudo-3d model. The effects of perforation cluster spacing, differential stress (SHmax - Shmin) and various geometry natural fracture patterns on injection pressure and fracture complexity were investigated. The single stage simulation results shown that (1) higher differential stress suppresses fracture length and increases injection pressure; (2) there is an optimal choice for the number of fractures per stage to maximize effective fracture surface area, beyond which increasing the number of fractures actually decreases effective fracture area; and (3) fracture complexity is a function of natural fracture patterns (various regular pattern geometries were investigated). Natural fractures with small relative angle to hydraulic fractures are more likely to control fracture propagation path. Also, natural fracture patterns with more long fractures tend to increase the likelihood to dominate the preferential fracture trend of fracture trajectory. Our numerical model can provide a physics-based complex fracture network that can be imported into reservoir simulation models for production analysis. The overall sensitivity results presented should serve as guidelines for fracture complexity analysis.

A Peridynamics Model for the Propagation of Hydraulic Fractures in Heterogeneous, Naturally Fractured Reservoirs

2015 ◽  
Author(s):  
Hisanao Ouchi ◽  
Amit Katiyar ◽  
John T. Foster ◽  
Mukul M. Sharma
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Fracture Propagation ◽  
Two Dimensions ◽  
Natural Fracture ◽  
Hydraulic Fractures ◽  
Natural Fractures ◽  
Fracture Networks ◽  
Complex Fracture ◽  
Nonlocal Continuum Theory

Abstract A novel fully coupled hydraulic fracturing model based on a nonlocal continuum theory of peridynamics is presented and applied to the fracture propagation problem. It is shown that this modeling approach provides an alternative to finite element and finite volume methods for solving poroelastic and fracture propagation problems and offers some clear advantages. In this paper we specifically investigate the interaction between a hydraulic fracture and natural fractures. Current hydraulic fracturing models remain limited in their ability to simulate the formation of non-planar, complex fracture networks. The peridynamics model presented here overcomes most of the limitations of existing models and provides a novel approach to simulate and understand the interaction between hydraulic fractures and natural fractures. The model predictions in two-dimensions have been validated by reproducing published experimental results where the interaction between a hydraulic fracture and a natural fracture is controlled by the principal stress contrast and the approach angle. A detailed parametric study involving poroelasticity and mechanical properties of the rock is performed to understand why a hydraulic fracture gets arrested or crosses a natural fracture. This analysis reveals that the poroelasticity, resulting from high fracture fluid leak-off, has a dominant influence on the interaction between a hydraulic fracture and a natural fracture. In addition, the fracture toughness of the rock, the toughness of the natural fracture, and the shear strength of the natural fracture also affect the interaction between a hydraulic fracture and a natural fracture. Finally, we investigate the interaction of multiple completing fractures with natural fractures in two-dimensions and demonstrate the applicability of the approach to simulate complex fracture networks on a field scale.

Thermal Effects on Far-Field Distributed Acoustic Strain-Rate Sensors

2021 ◽  
Author(s):  
Smith Edward Leggett ◽  
Ding Zhu ◽  
Alfred Daniel Hill
Keyword(s):  
Phase Shift ◽  
Temperature Gradient ◽  
Strain Rate ◽  
Hydraulic Fracture ◽  
Thermal Effects ◽  
Temperature Effects ◽  
Fiber Optic ◽  
Displacement Discontinuity ◽  
Observation Well ◽  
Optical Phase

Abstract Fiber-optic cables cemented outside of the casing of an unconventional well measure cross-well strain changes during fracturing of neighboring wells with low-frequency distributed acoustic sensing (LF-DAS). As a hydraulic fracture intersects an observation well instrumented with fiber-optic cables, fracture fluid injected at ambient temperatures can cool a section of the sensing fiber. Often, LF-DAS and distributed temperature sensing (DTS) cables are run in tandem, enabling the detection of such cooling events. The increasing use of LF-DAS for characterizing unconventional hydraulic fracture completions demands an investigation of the effects of temperature on the measured strain response by LF-DAS. Researchers have demonstrated that LF-DAS can be used to extract the temporal derivative of temperature for use as a differential-temperature-gradient sensor. However, differential-temperature-gradient sensing is predicated on the ability to filter strain components out of the optical signal. In this work, beginning with an equation for optical phase shift of LF-DAS signals, a model relating strain, temperature, and optical phase shift is explicitly developed. The formula provides insights into the relative strength of strain and temperature effects on the phase shift. The uncertainty in the strain-rate measurements due to thermal effects is estimated. The relationship can also be used to quantify uncertainties in differential-temperature-gradient sensors due to strain perturbations. Additionally, a workflow is presented to simulate the LF-DAS response accounting for both strain and temperature effects. Hydraulic fracture geometries are generated with a 3D fracture simulator for a multi-stage unconventional completion. The fracture width distributions are imported by a displacement discontinuity method program to compute the strain-rates along an observation well. An analytic model is used to approximate the temperature in the fracture. Using the derived formulae for optical phase shift, the model outputs are then used to compute the LF-DAS response at a fiber-optic cable, enabling the generation of waterfall plots including both strain and thermal effects. The model results suggest that before, during, and immediately following a fracture intersecting a well instrumented with fiber, the strain on the fiber drives the LF-DAS signal. However, at later times, as completion fluid cools the observation well, the temperature component of the LF-DAS signal can equal or exceed the strain component. The modeled results are compared to a published field case in an attempt to enhance interpretation of LF-DAS waterfall plots. Finally, we propose a sensing configuration in order to identify the events when "wet fractures" (fractures with fluids) intersect the observation well.

Interpreting Uncemented Multistage Hydraulic-Fracturing Completion Effectiveness By Use of Fiber-Optic DTS Injection Data

2013 ◽  
Vol 28 (03) ◽  
pp. 243-253 ◽  
Author(s):  
Eric H. Holley ◽  
Menno M. Molenaar ◽  
Erkan Fidan ◽  
Ben Banack
Keyword(s):  
Hydraulic Fracturing ◽  
Fiber Optic ◽  
Multistage Hydraulic Fracturing

Geomechanical Template for Distributed Acoustic Sensing Strain Patterns during Hydraulic Fracturing

SPE Journal ◽  
2021 ◽  
pp. 1-12
Author(s):  
Yunhui Tan ◽  
Shugang Wang ◽  
Margaretha C. M. Rijken ◽  
Kelly Hughes ◽  
Ivan Lim Chen Ning ◽  
...  
Keyword(s):  
Finite Element ◽  
Hydraulic Fracturing ◽  
Strain Rate ◽  
Hydraulic Fracture ◽  
Strain Field ◽  
Low Frequency ◽  
Fracture Propagation ◽  
Fracture Network ◽  
Hydraulic Fractures ◽  
Distributed Acoustic Sensing

Summary Recently more distributed acoustic sensing (DAS) data have been collected during hydraulic fracturing in shale. Low-frequency DAS signals show patterns that are intuitively consistent with the understanding of the strain field around hydraulic fractures. This study uses a fracture simulator combined with a finite element solver to further understand the various patterns of the strain field caused by hydraulic fracturing. The results can serve as a “type-curve” template for the further interpretation of cross-well strain field plots. Incorporating detailed pump schedule and fracturing fluid/proppant properties, we use a hydraulic fracture simulator to generate fracture geometries, which are then passed to a finite element solver as boundary conditions for elastic-static calculation of the strain field. Because the finite element calculated strain is a tensor, it needs to be projected along the monitoring well trajectory to be comparable with the DAS strain, which is uniaxial. Moreover, the calculated strain field is transformed into a time domain using constant fracture propagation velocity. Strain rate is further derived from the simulated strain field using differentiation along the fracture propagation direction. Scenarios including a single planar hydraulic fracture, a single fracture with a discrete fracture network (DFN), and multiple planar hydraulic fractures in both vertical and horizontal directions were studied. The scenarios can be differentiated in the strain patterns on the basis of the finite element simulation results. In general, there is a tensile heart-shaped zone in front of the propagating fracture tip shown along the horizontal strain direction on both strain and strain rate plots. On the sides, there are compressional zones parallel to the fracture. The strain field projects beyond the depth where the hydraulic fracture is present. Patterns from strain rate can be used to distinguish whether the fracture is intersecting the fiber. Along the vertical direction, the transition zone depicts the upper boundary of the fracture. A complex fracture network with DFN shows a much more complex pattern compared with a single planar fracture. Multiple planar fractures show polarity reversals in horizontal fiber because of interactions between fractures. Data from the Hydraulic Fracturing Test Site 2 (HFTS2) experiment were used to validate the simulated results. The application of the study is to provide a template to better interpret hydraulic fracture characteristics using low-frequency DAS strain-monitoring data. To our understanding, there are no comprehensive templates for engineers to understand the strain signals from cross-well fiber monitoring. The results of this study will guide engineers toward better optimization of well spacing and fracturing design to minimize well interference and improve efficiency.

Tiltmeter Mapping of Measured Nonsymmetric Hydraulic-Fracture Growth in a Conglomerate/Sandstone Formation Using the Implicit Level-Set Algorithm and the Extended Kalman Filter

SPE Journal ◽  
2017 ◽  
Vol 23 (01) ◽  
pp. 172-185
Author(s):  
V.. Pandurangan ◽  
A.. Peirce ◽  
Z. R. Chen ◽  
R. G. Jeffrey
Keyword(s):  
Kalman Filter ◽  
Hydraulic Fracturing ◽  
Dynamic Model ◽  
Extended Kalman Filter ◽  
Level Set ◽  
Hydraulic Fracture ◽  
Field Data ◽  
Fracture Propagation ◽  
Physical Processes ◽  
Fracture Growth

Summary A novel method to map asymmetric hydraulic-fracture propagation using tiltmeter measurements is presented. Hydraulic fracturing is primarily used for oil-and-gas well stimulation, and is also applied to precondition rock before mining. The geometry of the developing fracture is often remotely monitored with tiltmeters—instruments that are able to remotely measure the fracture-induced deformations. However, conventional analysis of tiltmeter data is limited to determining the fracture orientation and volume. The objective of this work is to detect asymmetric fracture growth during a hydraulic-fracturing treatment, which will yield height-growth information for vertical fracture growth and horizontal asymmetry for lateral fracture growth or detect low preconditioning-treatment efficiency in mining. The technique proposed here uses the extended Kalman filter (EKF) to assimilate tilt data into a hydraulic-fracture model to track the geometry of the fracture front. The EKF uses the implicit level set algorithm (ILSA) as the dynamic model to locate the boundary of the fracture by solving the coupled fluid-flow/fracture-propagation equations, and uses the Okada half-space solution as the observation model (forward model) to relate the fracture geometry to the measured tilts. The 3D fracture model uses the Okada analytical expressions for the displacements and tilts caused by piecewise constant-displacement discontinuity elements to discretize the fracture area. The proposed technique is first validated by a numerical example in which synthetic tilt data are generated by assuming a confining-stress gradient to generate asymmetric fracture growth. The inversion is carried in a two-step process in which the fracture dip and dip direction are first obtained with an elliptical fracture-forward model, and then the ILSA-EKF model is used to obtain the fracture footprint by fixing the dip and dip direction to the values obtained in the first step. Finally, the ILSA-EKF scheme is used to predict the fracture width and geometry evolution from real field data, which are compared with intersection data obtained by temperature and pressure monitoring in offset boreholes. The results show that the procedure is able to satisfactorily capture fracture growth and asymmetry even though the field data contain significant noise, the tiltmeters are relatively far from the fracture, and the dynamic model contains significant “unmodeled dynamics” such as stress anisotropy, material heterogeneity, fluid leakoff into the formation, and other physical processes that have not been explicitly accounted for in the dynamic ILSA model. However, all the physical processes that affect the tilt signal are incorporated by the EKF when the tilt measurements are used to obtain the maximum likelihood estimates of the fracture widths and geometry.

Thermal Effects on Far-Field Distributed Acoustic Strain-Rate Sensors

SPE Journal ◽  
2021 ◽  
pp. 1-13
Author(s):  
Smith Edward Leggett ◽  
Ding Zhu ◽  
Alfred Daniel Hill
Keyword(s):  
Phase Shift ◽  
Temperature Gradient ◽  
Strain Rate ◽  
Hydraulic Fracture ◽  
Thermal Effects ◽  
Temperature Effects ◽  
Fiber Optic ◽  
Displacement Discontinuity ◽  
Observation Well ◽  
Optical Phase

Summary Fiber-optic cables cemented outside of the casing of an unconventional well measure crosswell strain changes during fracturing of neighboring wells with low-frequency distributed acoustic sensing (LF-DAS). As a hydraulic fracture intersects an observation well instrumented with fiber-optic cables, the fracture fluid injected at ambient temperatures can cool a section of the sensing fiber. Often, LF-DAS and distributed temperature sensing (DTS) cables are run in tandem, enabling the detection of such cooling events. The increasing use of LF-DAS for characterizing unconventional hydraulic fracture completions demands an investigation of the effects of temperature on the measured strain response by LF-DAS. Researchers have demonstrated that LF-DAS can be used to extract the temporal derivative of temperature for use as a differential-temperature-gradient sensor. However, differential-temperature-gradient sensing is predicated on the ability to filter strain components out of the optical signal. In this work, beginning with an equation for optical phase shift of LF-DAS signals, a model relating strain, temperature, and optical phase shift is explicitly developed. The formula provides insights into the relative strength of strain and temperature effects on the phase shift. The uncertainty in the strain-rate measurements due to thermal effects is estimated. The relationship can also be used to quantify uncertainties in differential-temperature-gradient sensors due to strain perturbations. Additionally, a workflow is presented to simulate the LF-DAS response accounting for both strain and temperature effects. Hydraulic fracture geometries are generated with a 3D fracture simulator for a multistage unconventional completion. The fracture width distributions are imported by a displacement discontinuity method (DDM) program to compute the strain rates along an observation well. An analytic model is used to approximate the temperature in the fracture. Using the derived formulae for optical phase shift, the model outputs are then used to compute the LF-DAS response at a fiber-optic cable, enabling the generation of waterfall plots including both strain and thermal effects. The model results suggest that before, during, and immediately following a fracture intersecting a well instrumented with fiber, the strain on the fiber drives the LF-DAS signal. However, at later times, as completion fluid cools the observation well, the temperature component of the LF-DAS signal can be equal to or exceed the strain component. The modeled results are compared to a published field case in an attempt to enhance the interpretation of LF-DAS waterfall plots. Finally, we propose a sensing configuration to identify the events when “wet fractures” (fractures with fluids) intersect the observation well.

Sign in / Sign up

Export Citation Format

Share Document