The 4D microgravity method for waterflood surveillance: Part II — Gravity measurements for the Prudhoe Bay reservoir, Alaska

Between 1994 and 2002, a series of experiments was conducted at Prudhoe Bay, Alaska, aimed at the development of an effective 4D (or time-lapse) gravity technique. Theoretical investigations had pointed out the potential for monitoring water injection in the [Formula: see text]-deep reservoir, but it was not clear that gravity measurements of sufficient accuracy could be made in the arctic environment. During the course of these experiments, new techniques and instrumentation were introduced and perfected for both gravity and position measurements. Gravity stations are located using high-precision global positioning system (GPS) techniques without permanent monuments. Robust methods for meter drift control have improved noise resistance in relative gravimeter surveys. Absolute gravity measurements with a field-portable instrument maintain absolute gravity levels among surveys. A 4D gravity-difference noise of [Formula: see text] standard deviation has been established at Prudhoe Bay for GPS-controlled relative gravimeter surveys. The lessons learned are now being applied to full-scale waterflood monitoring at Prudhoe Bay. The basic technique is applicable to microgravity surveys and 4D microgravity surveys for any purpose.

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Ten years of time-lapse seismic on Atlantis Field

The Leading Edge ◽

10.1190/tle40070494.1 ◽

2021 ◽

Vol 40 (7) ◽

pp. 494-501

Author(s):

Jean-Paul van Gestel

Keyword(s):

Waveform Inversion ◽

Water Injection ◽

Main Tool ◽

Time Lapse ◽

Velocity Model ◽

Lessons Learned ◽

Ocean Bottom ◽

Injection Wells ◽

History Match ◽

Business Decisions

In 2019, the fourth ocean-bottom-node survey was acquired over Atlantis Field. This survey was quickly processed to provide useful time-lapse (4D) observations two months after the end of the acquisition. The time-lapse observations were immediately valuable in placing wells, refining final drilling target locations, updating well prioritization, and sequencing production and water-injection wells. These data are indispensable pieces of information that bring geophysicists and reservoir engineers together and focus the conversation on key remaining uncertainties such as fault transmissibilities and drainage areas. Time-lapse observations can confirm the key conceptional models already in place but are even more valuable when they highlight alternative models that have not yet been considered. The lessons learned from the acquisition, processing, analysis, interpretation, and integration of the data are shared. Some of these lessons are reiterations of previous work, but several new lessons originated from the latest 2019 acquisition. This was the first survey in which independent simultaneous sources were successfully deployed to collect a time-lapse survey. This resulted in a much faster and less expensive acquisition. In addition, full-waveform inversion was used as the main tool to update the velocity model, enabling a much faster turnaround in processing. The fast turnaround enabled incorporation of the latest acquisition to better constrain the velocity model update. The updated velocity model was used for the final time-lapse migration. In the integration part, the 4D-assisted history-match workflow was engaged to update the reservoir model history match. All of the upgrades led to an overall faster, less expensive, and better way to incorporate the acquired data in the final business decisions.

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Geothermal reservoir monitoring with a combination of absolute and relative gravimetry

Geophysics ◽

10.1190/1.2991105 ◽

2008 ◽

Vol 73 (6) ◽

pp. WA37-WA47 ◽

Cited By ~ 32

Author(s):

Mituhiko Sugihara ◽

Tsuneo Ishido

Keyword(s):

History Matching ◽

Observation Interval ◽

Time Lapse ◽

Gravity Measurement ◽

Absolute Gravity ◽

Short Term ◽

Well Production ◽

Gravity Measurements ◽

Central Production

Microgravity monitoring is a valuable tool for mapping the redistribution of subsurface mass and for assessing changes in fluid recharge from reservoir boundaries associated with geothermal exploitation. To further the development of a high-precision absolute/relative hybrid gravity-measurement technique, we conducted measurements using an absolute gravimeter in two geothermal fields in Japan. The absolute gravity measurements were performed in the central production areas to directly measure gravity changes caused by fluid withdrawal. We succeeded in measuring long-term trends within an accuracy of a few microgals in the Okuaizu and Ogiri fields, which have been producing electricity for several years. Absolute measurements in the center of the field provide reliable and local reference datum anchor points for more widely distributed relative gravity measurements. In the Ogiri field, we carried out time-lapse hybrid measurements with this combination of absolute and relative gravimetry and delineated the spatial distributions of long- and short-term changes. The long-term changes are relatively small, considering the four-year observation interval. This suggests a near balance between the mass withdrawal rate from wells and mass recharge from peripheral regions. The apparent balance is reproduced fairly well by a preliminary numerical reservoir simulation study. The observed long- and short-term changes are thought to be useful constraints for planned history-matching studies based on refined reservoir models with greater spatial resolution that incorporate detailed well-by-well production histories.

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Preliminary absolute gravity survey results from water injection monitoring program at Prudhoe Bay

10.1190/1.1817378 ◽

2002 ◽

Cited By ~ 2

Author(s):

J. M. Brown ◽

F. J. Klopping ◽

D. van Westrum ◽

T. M. Niebauer ◽

R. Billson ◽

...

Keyword(s):

Water Injection ◽

Monitoring Program ◽

Gravity Survey ◽

Absolute Gravity ◽

Survey Results ◽

Prudhoe Bay

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Forty-three years of absolute gravity observations of the Fennoscandian postglacial rebound in Finland

Journal of Geodesy ◽

10.1007/s00190-020-01470-9 ◽

2021 ◽

Vol 95 (2) ◽

Author(s):

Mirjam Bilker-Koivula ◽

Jaakko Mäkinen ◽

Hannu Ruotsalainen ◽

Jyri Näränen ◽

Timo Saari

Keyword(s):

Gravity Data ◽

Gravity Change ◽

Global Navigation Satellite Systems ◽

Absolute Gravity ◽

Data Sets ◽

Postglacial Rebound ◽

Land Uplift ◽

Satellite Systems ◽

Gravity Measurements ◽

Global Navigation Satellite

AbstractPostglacial rebound in Fennoscandia causes striking trends in gravity measurements of the area. We present time series of absolute gravity data collected between 1976 and 2019 on 12 stations in Finland with different types of instruments. First, we determine the trends at each station and analyse the effect of the instrument types. We estimate, for example, an offset of 6.8 μgal for the JILAg-5 instrument with respect to the FG5-type instruments. Applying the offsets in the trend analysis strengthens the trends being in good agreement with the NKG2016LU_gdot model of gravity change. Trends of seven stations were found robust and were used to analyse the stabilization of the trends in time and to determine the relationship between gravity change rates and land uplift rates as measured with global navigation satellite systems (GNSS) as well as from the NKG2016LU_abs land uplift model. Trends calculated from combined and offset-corrected measurements of JILAg-5- and FG5-type instruments stabilized in 15 to 20 years and at some stations even faster. The trends of FG5-type instrument data alone stabilized generally within 10 years. The ratio between gravity change rates and vertical rates from different data sets yields values between − 0.206 ± 0.017 and − 0.227 ± 0.024 µGal/mm and axis intercept values between 0.248 ± 0.089 and 0.335 ± 0.136 µGal/yr. These values are larger than previous estimates for Fennoscandia.

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Flake Dispersal Experiments: Noncultural Transformation of the Archaeological Record

American Antiquity ◽

10.2307/280562 ◽

1983 ◽

Vol 48 (3) ◽

pp. 553-572 ◽

Cited By ~ 31

Author(s):

Peter M. Bowers ◽

Robson Bonnichsen ◽

David M. Hoch

Keyword(s):

Human Activity ◽

Time Lapse ◽

Primary Factor ◽

Frost Heave ◽

The Arctic ◽

Archaeological Sites ◽

Archaeological Record ◽

Alaska Range ◽

Natural Processes ◽

Present Test

Time lapse studies of frost action effects on arctic and subarctic surficial archaeological sites have been conducted from 1973 to the present. Test plots of experimentally produced flakes were constructed in 1973 in the Tangle Lakes Region of the Central Alaska Range and subsequently remapped and photographed in 1974, 1976, and 1980. Similar test plots were laid out in the arctic foothills province of the Brooks Range. Observations made during the study period include: (1) flake displacements of as much as 20 cm/yr; (2) average minimum movement is 4 cm/yr; and (3) upslope movements were observed, suggesting that slope is not the primary factor in flake displacements. Frost heave, needle ice and, possibly, wind appear to be the dominant forces responsible for dispersals. It is argued that these and other natural processes can restructure the archaeological record into patterns that easily can be mistaken for those produced by human activity.

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Estimating saturation and density changes caused by CO2 injection at Sleipner — Using time-lapse seismic amplitude-variation-with-offset and time-lapse gravity

Interpretation ◽

10.1190/int-2016-0120.1 ◽

2017 ◽

Vol 5 (2) ◽

pp. T243-T257 ◽

Cited By ~ 11

Author(s):

Martin Landrø ◽

Mark Zumberge

Keyword(s):

Gravity Data ◽

Time Lapse ◽

Co2 Injection ◽

Injection Point ◽

Amplitude Variation With Offset ◽

Seismic Method ◽

Seismic Amplitude ◽

Gravity Measurements ◽

Measured Time ◽

Best Fit

We have developed a calibrated, simple time-lapse seismic method for estimating saturation changes from the [Formula: see text]-storage project at Sleipner offshore Norway. This seismic method works well to map changes when [Formula: see text] is migrating laterally away from the injection point. However, it is challenging to detect changes occurring below [Formula: see text] layers that have already been charged by some [Formula: see text]. Not only is this partly caused by the seismic shadow effects, but also by the fact that the velocity sensitivity for [Formula: see text] change in saturation from 0.3 to 1.0 is significantly less than saturation changes from zero to 0.3. To circumvent the seismic shadow zone problem, we combine the time-lapse seismic method with time-lapse gravity measurements. This is done by a simple forward modeling of gravity changes based on the seismically derived saturation changes, letting these saturation changes be scaled by an arbitrary constant and then by minimizing the least-squares error to obtain the best fit between the scaled saturation changes and the measured time-lapse gravity data. In this way, we are able to exploit the complementary properties of time-lapse seismic and gravity data.

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