Time-lapse changes within the Groningen gas field caused reservoir by compaction and distant borehole drilling

2020 ◽  
Author(s):  
Hanneke Paulssen ◽  
Wen Zhou
Keyword(s):  
Travel Time ◽  
Pore Pressure ◽  
Velocity Structure ◽  
Time Lapse ◽  
P Wave ◽  
S Wave ◽  
Gas Field ◽  
Water Contact ◽  
Wave Travel ◽  
Groningen Gas Field

<p>Between 2013 and 2017, the Groningen gas field was monitored by several deployments of an array of geophones in a deep borehole at reservoir level (3 km). Zhou & Paulssen (2017) showed that the P- and S-velocity structure of the reservoir could be retrieved from noise interferometry by cross-correlation. Here we show that deconvolution interferometry of high-frequency train signals from a nearby railroad not only allows determination of the velocity structure with higher accuracy, but also enables time-lapse measurements. We found that the travel times within the reservoir decrease by a few tens of microseconds for two 5-month periods. The observed travel time decreases are associated to velocity increases caused by compaction of the reservoir. However, the uncertainties are relatively large. <br>Striking is the large P-wave travel time anomaly (-0.8 ms) during a distinct period of time (17 Jul - 2 Sep 2015). It is only observed for inter-geophone paths that cross the gas-water contact (GWC) of the reservoir. The anomaly started 4 days after drilling into the reservoir of a new well at 4.5 km distance and ended 4 days after the drilling operations stopped. We did not find an associated S-wave travel time anomaly. This suggests that the anomaly is caused by a temporary elevation of the GWC (water replacing gas) of approximately 20 m. We suggest that the GWC is elevated due to pore-pressure variations during drilling. The 4-day delay corresponds to a pore-pressure diffusivity of ~5m<sup>2</sup>/s, which is in good agreement with the value found from material parameters and the diffusivity of (induced) seismicity for various regions in the world. </p>

scholarly journals Compaction of the Groningen gas reservoir investigated with train noise

2020 ◽  
Vol 223 (2) ◽  
pp. 1327-1337
Author(s):  
Wen Zhou ◽  
Hanneke Paulssen
Keyword(s):  
Velocity Structure ◽  
Temporal Variations ◽  
P Wave ◽  
Deep Borehole ◽  
S Wave ◽  
Borehole Data ◽  
Noise Sources ◽  
Gas Field ◽  
Reservoir Compaction ◽  
Noise Data

Summary Induced seismicity in the Groningen gas field in the Netherlands has been related to reservoir compaction caused by gas pressure depletion. In situ measurement of compaction is therefore relevant for seismic hazard assessment. In this study, we investigated the potential of passively recorded deep borehole noise data to detect temporal variations in the Groningen reservoir. Train signals recorded by an array of 10 geophones at reservoir depth were selected from the continuous noise data for two 5-month deployments in 2015. Interferometry by deconvolution was applied to the high-frequency train signals that acted as stable, repetitive noise sources. Direct intergeophone P and S wave traveltimes were then used to construct the P- and S-wave velocity structure along the geophone array. The resulting models agree with independently obtained velocity profiles and have very small errors. Most intergeophone P wave traveltimes showed decreasing traveltimes per deployment period, suggestive of compaction. However, the retrieved traveltime changes are very small, up to tens of microseconds per deployment period, with uncertainties that are of similar size, about 10 microseconds. An unambiguous interpretation in terms of compaction is therefore not warranted, although the 10 μs error per 5-month period is probably smaller than can be achieved from active time-lapse seismic surveys that are commonly used to measure reservoir compaction. The direct P-wave amplitudes of the train-signal deconvolutions were investigated for additional imprints of compaction. Whereas the P-wave amplitudes consistently increased during the second deployment, suggestive of compaction, no such trend was observed for the first deployment, rendering the interpretation of compaction inconclusive. Our results therefore present hints, but no obvious effects of compaction in the Groningen reservoir. Yet, this study demonstrates that the approach of deconvolution interferometry applied to deep borehole data allows monitoring of small temporal changes in the subsurface for stable repetitive noise sources such as trains.

scholarly journals An Experimental and Modeling Study on the Response to Varying Pore Pressure and Reservoir Fluids in the Morrow A Sandstone

2012 ◽  
Vol 2012 ◽  
pp. 1-17 ◽  
Author(s):  
Aaron V. Wandler ◽  
Thomas L. Davis ◽  
Paritosh K. Singh
Keyword(s):  
Pore Pressure ◽  
Wave Velocity ◽  
Oil Recovery ◽  
Laboratory Experiments ◽  
Time Lapse ◽  
P Wave ◽  
Well Logs ◽  
S Wave ◽  
Core Samples ◽  
Fluid Saturation

In mature oil fields undergoing enhanced oil recovery methods, such as CO2injection, monitoring the reservoir changes becomes important. To understand how reservoir changes influence compressional wave (P) and shear wave (S) velocities, we conducted laboratory core experiments on five core samples taken from the Morrow A sandstone at Postle Field, Oklahoma. The laboratory experiments measured P- and S-wave velocities as a function of confining pressure, pore pressure, and fluid type (which included CO2in the gas and supercritical phase). P-wave velocity shows a response that is sensitive to both pore pressure and fluid saturation. However, S-wave velocity is primarily sensitive to changes in pore pressure. We use the fluid and pore pressure response measured from the core samples to modify velocity well logs through a log facies model correlation. The modified well logs simulate the brine- and CO2-saturated cases at minimum and maximum reservoir pressure and are inputs for full waveform seismic modeling. Modeling shows how P- and S-waves have a different time-lapse amplitude response with offset. The results from the laboratory experiments and modeling show the advantages of combining P- and S-wave attributes in recognizing the mechanism responsible for time-lapse changes due to CO2injection.

The effects of seismic anisotropy on  S-wave travel time-tomography: the problem of apparent anomalies and possible solutions

2021 ◽  
Author(s):  
Francesco Rappisi ◽  
Brandon Paul Vanderbeek ◽  
Manuele Faccenda
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
Shear Velocity ◽  
P Wave ◽  
Travel Times ◽  
S Wave ◽  
Velocity Models ◽  
Travel Time Tomography ◽  
Wave Travel ◽  
Wave Tomography

<p>Teleseismic travel-time tomography remains one of the most popular methods for obtaining images of Earth's upper mantle. While teleseismic shear phases, most notably SKS, are commonly used to infer the anisotropic properties of the upper mantle, anisotropic structure is often ignored in the construction of body wave shear velocity models. Numerous researchers have demonstrated that neglecting anisotropy in P-wave tomography can introduce significant imaging artefacts that could lead to spurious interpretations. Less attention has been given to the effect of anisotropy on S-wave tomography partly because, unlike P-waves, there is not a ray-based methodology for modelling S-wave travel-times through anisotropic media. Here we evaluate the effect that the isotropic approximation has on tomographic images of the subsurface when shear waves are affected by realistic mantle anisotropy patterns. We use SPECFEM to model the teleseismic shear wavefield through a geodynamic model of subduction that includes elastic anisotropy predicted from micromechanical models of polymineralic aggregates advected through the simulated flow field. We explore how the chosen coordinates system in which S-wave arrival times are measured (e.g., radial versus transverse) affects the imaging results. In all cases, the isotropic imaging assumption leads to numerous artefacts in the recovered velocity models that could result in misguided inferences regarding mantle dynamics. We find that when S-wave travel-times are measured in the direction of polarisation, the apparent anisotropic shear velocity can be approximated using sinusoidal functions of period pi and two-pi. This observation allows us to use ray-based methods to predict S-wave travel-times through anisotropic models. We show that this parameterisation can be used to invert S-wave travel-times for the orientation and strength of anisotropy in a manner similar to anisotropic P-wave travel-time tomography. In doing so, the magnitude of imaging artefacts in the shear velocity models is greatly reduced.</p>

scholarly journals Teleseismic P-wave travel time and amplitude anomalies observed in Hokkaido region, Japan.

1990 ◽  
Vol 38 (2) ◽  
pp. 163-177 ◽  
Author(s):  
Ichiro Nakanishi ◽  
Yoshinobu Motoya
Keyword(s):  
Travel Time ◽  
P Wave ◽  
Wave Travel

A new analytical method for finding the upper mantle velocity structure from P and S wave travel times of deep earthquakes

1969 ◽  
Vol 59 (2) ◽  
pp. 755-769
Author(s):  
K. L. Kaila
Keyword(s):  
Velocity Structure ◽  
Focal Depth ◽  
Least Square ◽  
Travel Times ◽  
S Wave ◽  
The Earth ◽  
Straight Line ◽  
Wave Travel ◽  
Deep Focus ◽  
Mantle Velocity

abstract A new analytical method for the determination of velocity at the hypocenter of a deep earthquake has been developed making use of P- and S-wave travel times. Unlike Gutenberg's method which is graphical in nature, the present method makes use of the least square technique and as such it yields more quantitative estimates of the velocities at depth. The essential features of this method are the determination from the travel times of a deep-focus earthquake the lower and upper limits Δ1 and Δ2 respectively of the epicentral distance between which p = (dT/dΔ) in the neighborhood of inflection point can be considered stationary so that the travel-time curve there can be approximated to a straight line T = pΔ + a. From p = (1/v*) determined from the straight line least-square fit made on the travel-time observation points between Δ1 and Δ2 for various focal depths, upper-mantle velocity structure can be obtained by making use of the well known relation v = v*(r0 − h)/r0, h being the focal depth of the earthquake, r0 the radius of the Earth, v* the apparent velocity at the point of inflection and v the true velocity at that depth. This method not only gives an accurate estimate of p, at the same time it also yields quite accurate value of a which is a function of focal depth. Calibration curves can be drawn between a and the focal depth h for various regions of the Earth where deep focus earthquakes occur, and these calibration curves can then be used with advantage to determine the focal depths of deep earthquakes in those areas.

Shallow velocity structure and poisson's ratio at the Tarzana, California, strong-motion accelerometer site

1996 ◽  
Vol 86 (6) ◽  
pp. 1704-1713 ◽  
Author(s):  
R. D. Catchings ◽  
W. H. K. Lee
Keyword(s):  
Urban Areas ◽  
Velocity Structure ◽  
Strong Motion ◽  
P Wave ◽  
S Wave ◽  
Near Surface ◽  
Velocity Models ◽  
Wave Velocities ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

Abstract The 17 January 1994, Northridge, California, earthquake produced strong ground shaking at the Cedar Hills Nursery (referred to here as the Tarzana site) within the city of Tarzana, California, approximately 6 km from the epicenter of the mainshock. Although the Tarzana site is on a hill and is a rock site, accelerations of approximately 1.78 g horizontally and 1.2 g vertically at the Tarzana site are among the highest ever instrumentally recorded for an earthquake. To investigate possible site effects at the Tarzana site, we used explosive-source seismic refraction data to determine the shallow (<70 m) P-and S-wave velocity structure. Our seismic velocity models for the Tarzana site indicate that the local velocity structure may have contributed significantly to the observed shaking. P-wave velocities range from 0.9 to 1.65 km/sec, and S-wave velocities range from 0.20 and 0.6 km/sec for the upper 70 m. We also found evidence for a local S-wave low-velocity zone (LVZ) beneath the top of the hill. The LVZ underlies a CDMG strong-motion recording site at depths between 25 and 60 m below ground surface (BGS). Our velocity model is consistent with the near-surface (<30 m) P- and S-wave velocities and Poisson's ratios measured in a nearby (<30 m) borehole. High Poisson's ratios (0.477 to 0.494) and S-wave attenuation within the LVZ suggest that the LVZ may be composed of highly saturated shales of the Modelo Formation. Because the lateral dimensions of the LVZ approximately correspond to the areas of strongest shaking, we suggest that the highly saturated zone may have contributed to localized strong shaking. Rock sites are generally considered to be ideal locations for site response in urban areas; however, localized, highly saturated rock sites may be a hazard in urban areas that requires further investigation.

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