Estimating geomechanical parameters from microseismic plane focal mechanisms recorded during multistage hydraulic fracturing

Geophysics ◽  
2017 ◽  
Vol 82 (1) ◽  
pp. KS1-KS11 ◽  
Author(s):  
Wenhuan Kuang ◽  
Mark Zoback ◽  
Jie Zhang
Keyword(s):  
Hydraulic Fracturing ◽  
Pore Pressure ◽  
Principal Stress ◽  
Focal Plane ◽  
Amplitude Ratio ◽  
Horizontal Stress ◽  
Focal Mechanisms ◽  
P Wave ◽  
S Wave ◽  
Multistage Hydraulic Fracturing

We extend a full-waveform modeling method to invert source focal-plane mechanisms for microseismic data recorded with dual-borehole seismic arrays. Combining inverted focal-plane mechanisms with geomechanics knowledge, we map the pore pressure distribution in the reservoir. Determining focal mechanisms for microseismic events is challenging due to poor geometry coverage. We use the P-wave polarities, the P- and S-wave similarities, the SV/P amplitude ratio, and the SH/P amplitude ratio to invert the focal-plane mechanisms. A synthetic study proves that this method can effectively resolve focal mechanisms with dual-array geometry. We apply this method to 47 relatively large events recorded during a hydraulic fracturing operation in the Barnett Shale. The focal mechanisms are used to invert for the orientation and relative magnitudes of the principal stress axes, the orientation of the planes slipping in shear, and the approximate pore pressure perturbation that caused the slip. The analysis of the focal mechanisms consistently shows a normal faulting stress state with the maximum principal stress near vertical, the maximum horizontal stress near horizontal at an azimuth of N60°E, and the minimum horizontal stress near horizontal at an azimuth of S30°E. We propose a general method that can be used to obtain microseismic focal-plane mechanisms and use them to improve the geomechanical understanding of the stimulation process during multistage hydraulic fracturing.

Hydrocarbon‐generation‐induced microcracking of source rocks

Geophysics ◽  
1994 ◽  
Vol 59 (4) ◽  
pp. 555-563 ◽  
Author(s):  
Lev Vernik
Keyword(s):  
Pore Pressure ◽  
Principal Stress ◽  
Sedimentary Basins ◽  
Confining Pressure ◽  
Black Shales ◽  
Source Rocks ◽  
P Wave ◽  
Hydrocarbon Generation ◽  
S Wave

Laboratory measurements of ultrasonic velocity and anisotropy in kerogen‐rich black shales of varying maturity suggest that extensive, bedding‐parallel microcracks exist in situ in most mature source rocks undergoing the major stage of hydrocarbon generation and migration. Given the normal faulting regime with the vertical stress being the maximum principal stress typical of most sedimentary basins, this microcrack alignment cannot be accounted for using simplified fracture mechanics concepts. This subhorizontal microcrack alignment is consistent with (1) a model of local principal stress rotation and deviatoric stress reduction within an overpressured formation undergoing hydrocarbon generation, and with (2) a strong mechanical strength anisotropy of kerogen‐rich shales caused by bedding‐parallel alignment of kerogen microlayers. Microcracks originate within kerogen or at kerogen‐illite interfaces when pore pressure exceeds the bedding‐normal total stress by only a few MPa due to the extremely low‐fracture toughness of organic matter. P‐wave and, especially, S‐wave anisotropy of the most mature black shales, measured as a function of confining pressure, indicate the effective closure pressure of these microcracks in the range from 10 to 25 MPa. Estimates of pore pressure cycles in the matrix of the active hydrocarbon‐generating/expelling part of the source rock formation show that microcracks can be maintained open over the sequence of these cycles and hence be detectable via high‐resolution in‐situ sonic/seismic studies.

The 1998 Valhall microseismic data set: An integrated study of relocated sources, seismic multiplets, and S-wave splitting

Geophysics ◽  
2009 ◽  
Vol 74 (5) ◽  
pp. B183-B195 ◽  
Author(s):  
K. De Meersman ◽  
J.-M. Kendall ◽  
M. van der Baan
Keyword(s):  
Seismic Anisotropy ◽  
Amplitude Ratio ◽  
Temporal Variations ◽  
Oil Field ◽  
P Wave ◽  
Wave Form ◽  
S Wave ◽  
Data Set ◽  
Wave Splitting ◽  
Source Mechanisms

We relocate 303 microseismic events recorded in 1998 by sensors in a single borehole in the North Sea Valhall oil field. A semiautomated array analysis method repicks the P- and S-wave arrival times and P-wave polarizations, which are needed to locate these events. The relocated sources are confined predominantly to a [Formula: see text]-thick zone just above the reservoir, and location uncertainties are half those of previous efforts. Multiplet analysis identifies 40 multiplet groups, which include 208 of the 303 events. The largest group contains 24 events, and five groups contain 10 or more events. Within each multiplet group, we further improve arrival-time picking through crosscorrelation, which enhances the relative accuracy of the relocated events and reveals that more than 99% of the seismic activity lies spatially in three distinct clusters. The spatial distribution of events and wave-form similarities reveal two faultlike structures that match well with north-northwest–south-southeast-trending fault planes interpreted from 3D surface seismic data. Most waveform differences between multiplet groups located on these faults can be attributed to S-wave phase content and polarity or P-to-S amplitude ratio. The range in P-to-S amplitude ratios observed on the faults is explained best in terms of varying source mechanisms. We also find a correlation between multiplet groups and temporal variations in seismic anisotropy, as revealed by S-wave splitting analysis. We explain these findings in the context of a cyclic recharge and dissipation of cap-rock stresses in response to production-driven compaction of the underlying oil reservoir. The cyclic nature of this mechanism drives the short-term variations in seismic anisotropy and the reactivation of microseismic source mechanisms over time.

Amplitude-based misfit functions in viscoelastic full-waveform inversion applied to walk-away vertical seismic profile data

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. B335-B351 ◽  
Author(s):  
Wenyong Pan ◽  
Kristopher A. Innanen
Keyword(s):  
Amplitude Ratio ◽  
Waveform Inversion ◽  
Seismic Profile ◽  
P Wave ◽  
Western Canada ◽  
Full Waveform Inversion ◽  
Walk Away ◽  
Profile Data ◽  
S Wave ◽  
Full Waveform

Viscoelastic full-waveform inversion is applied to walk-away vertical seismic profile data acquired at a producing heavy-oil field in Western Canada for the determination of subsurface velocity models (P-wave velocity [Formula: see text] and S-wave velocity [Formula: see text]) and attenuation models (P-wave quality factor [Formula: see text] and S-wave quality factor [Formula: see text]). To mitigate strong velocity-attenuation trade-offs, a two-stage approach is adopted. In Stage I, [Formula: see text] and [Formula: see text] models are first inverted using a standard waveform-difference (WD) misfit function. Following this, in Stage II, different amplitude-based misfit functions are used to estimate the [Formula: see text] and [Formula: see text] models. Compared to the traditional WD misfit function, the amplitude-based misfit functions exhibit stronger sensitivity to attenuation anomalies and appear to be able to invert [Formula: see text] and [Formula: see text] models more reliably in the presence of velocity errors. Overall, the root-mean-square amplitude-ratio and spectral amplitude-ratio misfit functions outperform other misfit function choices. In the final outputs of our inversion, significant drops in the [Formula: see text] to [Formula: see text] ratio (~1.6) and Poisson’s ratio (~0.23) are apparent within the Clearwater Formation (depth ~0.45–0.50 km) of the Mannville Group in the Western Canada Sedimentary Basin. Strong [Formula: see text] (~20) and [Formula: see text] (~15) anomalies are also evident in this zone. These observations provide information to help identify the target attenuative reservoir saturated with heavy-oil resources.

The role of preexisting fractures and faults during multistage hydraulic fracturing in the Bakken Formation

2014 ◽  
Vol 2 (3) ◽  
pp. SG25-SG39 ◽  
Author(s):  
Yi Yang ◽  
Mark D. Zoback
Keyword(s):  
Hydraulic Fracturing ◽  
Pore Pressure ◽  
Well Being ◽  
Williston Basin ◽  
Bakken Formation ◽  
Multistage Hydraulic Fracturing ◽  
Geomechanical Analysis ◽  
Microseismic Events ◽  
Observation Wells

We performed an integrated study of multistage hydraulic fracture stimulation of two parallel horizontal wells in the Bakken Formation in the Williston Basin, North Dakota. There are three distinct parts of this study: development of a geomechanical model for the study area, interpretation of multiarray downhole recordings of microseismic events, and interpretation of hydraulic fracturing data in a geomechanical context. We estimated the current stress state to be characterized by an NF/SS regime, with [Formula: see text] oriented approximately [Formula: see text]. The microseismic events were recorded in six vertical observation wells during hydraulic fracturing of parallel wells X and Z with three unusual aspects. First, rather than occurring in proximity to the stages being pressurized, many of the events occurred along the length of well Y, a parallel well located between wells X and Z that had been in production for approximately [Formula: see text] years at the time X and Z were stimulated. Second, relatively few fracturing stages were associated with an elongated cloud of events trending in the direction of [Formula: see text] as was commonly observed during hydraulic fracturing. Instead, the microseismic events in a few stages appeared to trend approximately [Formula: see text], approximately 30° from the direction of [Formula: see text]. Earthquake focal plane mechanisms confirmed slip on faults with this orientation. Finally, the microseismic events were clustered at two distinct depths: one near the depth of the well being pressurized in the Middle Bakken Formation and the other approximately [Formula: see text] above in the Mission Canyon Formation. We proposed that steeply dipping N75°E striking faults with a combination of normal and strike-slip movement were being stimulated during hydraulic fracturing and provided conduits for pore pressure to be transmitted to the overlaying formations. We tested a simple geomechanical analysis to illustrate how this occurred in the context of the stress field, pore pressure, and depletion in the vicinity of well Y.

scholarly journals Prior Analysis in Determination of TI Anisotropy Type through Well-Based Modelling: A Case Study on the Deep Water Environment

2021 ◽  
Vol 873 (1) ◽  
pp. 012102
Author(s):  
Madaniya Oktariena ◽  
Wahyu Triyoso ◽  
Fatkhan Fatkhan ◽  
Sigit Sukmono ◽  
Erlangga Septama ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Deep Water ◽  
Initial Conditions ◽  
Transverse Isotropy ◽  
Water Environment ◽  
Horizontal Stress ◽  
P Wave ◽  
S Wave ◽  
Geomechanical Analysis ◽  
Vertical Transverse Isotropy

Abstract The existence of anisotropy phenomena in the subsurface will affect the image quality of seismic data. Hence a prior knowledge of the type of anisotropy is quite essential, especially when dealing with deep water targets. The preliminary result of the anisotropy of the well-based modelling in deep water exploration and development is discussed in this study. Anisotropy types are modelled for Vertical Transverse Isotropy (VTI) and Horizontal Transverse Isotropy (HTI) based on Thomsen Parameters of ε and γ. The parameters are obtained from DSI Logging paired with reference δ value for modelling. Three initial conditions are then analysed. The first assumption is isotropic, in which the P-Wave Velocity, S-Wave Velocity, and Density Log modelled at their in-situ condition. The second and third assumptions are anisotropy models that are VTI and HTI. In terms of HTI, the result shows that the model of CDP Gather in the offset domain has a weak distortion in Amplitude Variation with Azimuth (AVAz). However, another finding shows a relatively strong hockey effect in far offset, which indicates that the target level is a VTI dominated type. It is supported by the geomechanical analysis result in which vertical stress acts as the maximum principal axis while horizontal stress is close to isotropic one. To sum up, this prior anisotropy knowledge obtained based on this study could guide the efficiency guidance in exploring the deep water environment.

scholarly journals A Crack Propagation Control Study of Directional Hydraulic Fracturing Based on Hydraulic Slotting and a Nonuniform Pore Pressure Field

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Yugang Cheng ◽  
Zhaohui Lu ◽  
Xidong Du ◽  
Xuefu Zhang ◽  
Mengru Zeng
Keyword(s):  
Crack Initiation ◽  
Hydraulic Fracturing ◽  
Pore Pressure ◽  
Pressure Field ◽  
Process Analysis ◽  
Failure Process ◽  
Horizontal Stress ◽  
Directional Hydraulic Fracturing ◽  
Rock Failure Process ◽  
Initiation Pressure

Hydraulic fracturing techniques for developing deeply buried coal reservoirs face routine problems related to high initial pressures and limited control over the fracture propagation direction. A novel method of directional hydraulic fracturing (DHF) based on hydraulic slotting in a nonuniform pore pressure field is proposed. A mechanical model is used to address crack initiation and propagation in a nonuniform pore pressure field, where cracks tend to rupture and propagate towards zones of high pore pressure for reducing the effective rock stress more. The crack initiation pressure and propagation morphology are analyzed by rock failure process analysis software. The numerical results show that the directional propagation of hydraulic fracturing cracks is possible when the horizontal stress difference coefficient is less than or equal to 0.5 or the slotting deviation angle is less than or equal to 30°. These findings are in good agreement with experimental results, which support the accuracy and reliability of the proposed method and theory.

Geophysical response to dissolution of undisturbed and fractured evaporite rock during brine flow

2021 ◽  
Author(s):  
Michael Stanley Dale ◽  
Ismael Falcon-Suarez ◽  
Hector Marín-Moreno
Keyword(s):  
Pore Pressure ◽  
Human Life ◽  
Test Procedure ◽  
Pressure Effects ◽  
P Wave ◽  
Dissolution Process ◽  
Effective Pressure ◽  
S Wave ◽  
Supply Source ◽  
The Impact

<p>Dissolution of halite rock can significantly impact underground constructions (e.g., caverns for energy storage and abandoned caverns) and above ground constructions (e.g., highways and buildings) potentially causing a threat to human life from land subsidence and sinkhole hazards, instability to underground construction and pollutant release. In this work, we explore and quantify changes in elastic and hydromechanical properties during dissolution of halite rock by migration of water.</p><p>We evaluated the impact of dissolution on the geophysical properties of pristine (non-fractured) and fractured halite samples (with ~2.7% dolomite), using a synthetic (seawater-like) brine solution (3.5wt% NaCl). The dissolution test commenced by setting an initial effective pressure of 15 MPa (with minimum pore pressure of 0.1 MPa), equivalent to a depth of ~720 m below ground level. This confining pressure of 14.9 MPa ensured the adequate contact between sample and the ultrasonic instrumentation (P- and S-wave sensors), and the set of electrodes for electrical resistivity. The test procedure was set to investigate the effect of increasing pore pressure from 0.1 to 14 MPa on dissolution. This procedure was only successful for the non-fractured sample, as dissolution rapidly occurred in the fractured sample during the initial stage of the test.</p><p>The non-fractured halite shows that P-wave velocity increases with increasing inlet pore pressure initially, followed by a lower pore fluid sensitivity stage. After this stage, the P-wave and the Vp/Vs ratio reduce and then ultrasonic velocities tend to their original values when effective pressure tends to zero. These results suggest that capillary pressure effects are initially increasing the bulk properties of the rock by filling the micro-pores, while dissolution is occurring locally, nearby the inlet-flow port, and therefore invisible to our geophysical tools. The small porosity fraction of 1.1% allows the saturating fluid to rapidly equilibrate with the surrounding halite within the pores, slowing down the dissolution process. In a close halite system with a local and continuous brine supply source, local dissolution may allow pressure increase up to the overburden stress and affect the geomechanical integrity of the reservoir by a combined fracturing-dissolution process.</p>

The partition of radiated energy between P and S waves

1984 ◽  
Vol 74 (2) ◽  
pp. 361-376
Author(s):  
John Boatwright ◽  
Jon B. Fletcher
Keyword(s):  
Wave Energy ◽  
Body Wave ◽  
Focal Mechanisms ◽  
The Body ◽  
Body Waves ◽  
P Wave ◽  
Corner Frequency ◽  
S Wave ◽  
S Waves ◽  
Radiated Energy

Abstract Seventy-three digitally recorded body waves from nine multiply recorded small earthquakes in Monticello, South Carolina, are analyzed to estimate the energy radiated in P and S waves. Assuming Qα = Qβ = 300, the body-wave spectra are corrected for attenuation in the frequency domain, and the velocity power spectra are integrated over frequency to estimate the radiated energy flux. Focal mechanisms determined for the events by fitting the observed displacement pulse areas are used to correct for the radiation patterns. Averaging the results from the nine events gives 27.3 ± 3.3 for the ratio of the S-wave energy to the P-wave energy using 0.5 〈Fi〉 as a lower bound for the radiation pattern corrections, and 23.7 ± 3.0 using no correction for the focal mechanisms. The average shift between the P-wave corner frequency and the S-wave corner frequency, 1.24 ± 0.22, gives the ratio 13.7 ± 7.3. The substantially higher values obtained from the integral technique implies that the P waves in this data set are depleted in energy relative to the S waves. Cursory inspection of the body-wave arrivals suggests that this enervation results from an anomalous site response at two of the stations. Using the ratio of the P-wave moments to the S-wave moments to correct the two integral estimates gives 16.7 and 14.4 for the ratio of the S-wave energy to the P-wave energy.

Spectral analysis of body waves from the earthquake of February 18, 1956

1964 ◽  
Vol 54 (6A) ◽  
pp. 2017-2035 ◽  
Author(s):  
Tomowo Hirasawa ◽  
William Stauder
Keyword(s):  
Amplitude Ratio ◽  
Source Region ◽  
Focal Depth ◽  
Mean Amplitude ◽  
Theoretical Models ◽  
Body Waves ◽  
P Wave ◽  
Type I ◽  
Type Ii ◽  
S Wave

abstract The earthquake which occurred south of Honshu, Japan, on February 18, 1956 is studied by means of Fourier analysis. The focal depth of the shock is about 450 km and the magnitude is 714 to 712. Three theoretical models of the source mechanism, that is, Type Ia, Type Ib, and Type II, are examined by the observed amplitude spectra of S and ScS waves. It is found that the observed amplitude ratios of the Fourier components between two horizontal components of the S wave and of the ScS wave, respectively, agree well with the theoretical ratios for a Type II source. Under the assumption that spectral structures should be the same at all observing points, the scattering from the mean amplitude is calculated. The result shows that the Type II model is preferable to either of the Type I models. Assuming Honda's volume model, whose radiation pattern corresponds to that of a Type II point source, the radius of the source region is estimated by making use of the amplitude ratio of the Fourier component of the S wave to that of the P wave. The radius of the source is found to be 11 km ± 2 km.

Severe Casing Failure in Multistage Hydraulic Fracturing Using Dual-Scale Modelling Approach

2021 ◽  
Author(s):  
Hao Yu ◽  
Arash Dahi Taleghani ◽  
Zhanghua Lian ◽  
Yisheng Mou
Keyword(s):  
Hydraulic Fracturing ◽  
Positive Impact ◽  
Horizontal Stress ◽  
Fracture Network ◽  
Scale Model ◽  
Fracture Geometry ◽  
Multistage Hydraulic Fracturing ◽  
Field Evidence ◽  
Casing Deformation ◽  
Casing Failure

Abstract Field evidence of production logs after fracturing have documented the existence of abundant natural fractures in Weiyuan shale plays, which is widely acknowledged to have a positive impact on fracture network complexity. On the other hand, cases of severe casing failures have been frequently reported in this field during multistage fracturing jobs. Stress interference between two adjacent stages may intensify non-uniform loading on the casing string and accommodate failure. To better understand this problem, we establish a coupled 3D reservoir-scale model with complex well trajectory and tie it to a single well-scale model consisting of casing and the surrounding cement sheath. Using this model, we investigate the potential impacts of cement deficiency, clustered perforations, fracture geometry as well as spacing strategy on casing integrity. Our simulation results indicate that cement deficiency could intensify the load nonuniformity around the borehole which escalates the potential threats for casing failure. When cement deficiency reaches 45° along the minimum horizontal stress, it has the largest influence on the stress level in the casing. In addition, perforations could lower the casing strength, but the reduction may not change furthermore when the perforation diameter reaches a certain value. Moreover, impacts of fracture geometry and spacing on casing deformation are investigated. We conclude that the lower ratio of fracture length to its width and reasonable spacing strategy could help reduce the load non-uniformity on casing which avoid the casing deformation. The described workflow may be adopted in other areas to predict the possible casing failure problems induced by multistage hydraulic fracturing with cheap computational costs, to anticipate the challenges and avoid them by revisiting pumping schedule or spacing strategy.

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