Seismic detection of overpressuring and fracturing: An example from the Qaidam Basin, People’s Republic of China

Geophysics ◽  
1993 ◽  
Vol 58 (10) ◽  
pp. 1532-1543 ◽  
Author(s):  
Robert J. Paul
Keyword(s):  
Oil And Gas ◽  
Qaidam Basin ◽  
High Amplitude ◽  
Seismic Survey ◽  
Low Velocity ◽  
Velocity Anomaly ◽  
Deep Well ◽  
Significant Difference ◽  
Seismic Amplitudes ◽  
Definition Of

Shallow hydrocarbon reserves were discovered in 1959 in the Nan Yi Shan structure located near the western corner of the Qaidam Basin. The first successful deep well encountered an overpressured zone at 3000 m that resulted in a well blowout. To improve the structural definition of the field and delineate the overpressured layer a 3-D seismic survey was conducted. A region of anomalous seismic time sag associated with fracturing and small quantities of oil and gas was identified on the northwest plunging nose of the Nan Yi Shan anticline. The distribution of stacking (NMO) velocities in this region was regarded as abnormal; stacking velocities derived on the steeply dipping flanks adjacent to the sag anomaly were found to be slower than those on the shallower crest. Ray‐trace modeling of a buried low‐velocity anomaly provided a possible geometric solution to explain both the time variant nature of the sag and the unusual stacking velocity signature associated with it. A significant difference in seismic and sonic traveltimes was also observed for wells that penetrated the sag region and was attributed to localized fracturing. In a deeper interval, seismic amplitudes were used to identify gas‐saturated fracture porosity and to describe the spatial limits of overpressuring within a thin‐bed reservoir. Wells drilled through high‐amplitude anomalies encountered overpressuring, those drilled in a region of moderate seismic amplitude tested significant quantities of gas, and wells located outside the region of good coherent signal encountered poor or no hydrocarbon shows. These results demonstrate that with good quality seismic data and sufficient lateral and vertical resolution, thin fractured hydrocarbon‐bearing reservoirs can be delineated and overpressure zones identified.

scholarly journals Improved Seismic Monitoring with OBS Deployment in the Arctic: A Pilot Study from Offshore Western Svalbard

2021 ◽  
Author(s):  
Zeinab Jeddi ◽  
Lars Ottemöller ◽  
Mathilde Sørensen ◽  
Sara Rezaei ◽  
Steven Gibbons ◽  
...  
Keyword(s):  
Waveform Inversion ◽  
Arctic Region ◽  
The Arctic ◽  
Spreading Ridge ◽  
Ocean Bottom ◽  
Low Velocity ◽  
Arrival Times ◽  
Regional Seismicity ◽  
Velocity Anomaly ◽  
Significant Difference

The mid-ocean ridge system is the main source of earthquakes within the Arctic region. The earthquakes are recorded on the permanent land-based stations in the region, although smaller earthquakes remain undetected. In this study, we make use of three Ocean Bottom Seismographs (OBSs) that were deployed offshore western Svalbard, along the spreading ridges. The OBS arrival times were used to relocate the regional seismicity using a Bayesian approach, which resulted in a significant improvement with tighter clustering around the spreading ridge. We also extended the regional magnitude scales for the northern Atlantic region for OBSs by computing site correction terms. Besides location and magnitude improvement, the OBS network was able to detect hundreds of earthquakes, mostly with magnitude below Mw=3, including a swarm activity at the Molloy Deep. Our offshore observations provide further evidence of a low velocity anomaly offshore Svalbard, at the northern tip of Knipovich ridge, that was previously seen in full waveform inversion. We conclude that even a single permanent OBS near the ridge would make a significant difference to earthquake catalogs and their interpretation.

scholarly journals Improved Seismic Monitoring with OBS Deployment in the Arctic: A Pilot Study from Offshore Western Svalbard

2021 ◽  
Author(s):  
Zeinab Jeddi ◽  
Lars Ottemöller ◽  
Mathilde B. Sørensen ◽  
Sara Rezaei ◽  
Steven J. Gibbons ◽  
...  
Keyword(s):  
Waveform Inversion ◽  
Arctic Region ◽  
The Arctic ◽  
Spreading Ridge ◽  
Ocean Bottom ◽  
Low Velocity ◽  
Arrival Times ◽  
Regional Seismicity ◽  
Velocity Anomaly ◽  
Significant Difference

Abstract The mid-ocean ridge system is the main source of earthquakes within the Arctic region. The earthquakes are recorded on the permanent land-based stations in the region, although, smaller earthquakes remain undetected. In this study, we make use of three Ocean Bottom Seismographs (OBSs) that were deployed offshore western Svalbard, along the spreading ridges. The OBS arrival times were used to relocate the regional seismicity, using a Bayesian approach, which resulted in a significant improvement with tighter clustering around the spreading ridge. We also extended the regional magnitude scales for the northern Atlantic region for OBSs, by computing site correction terms. Besides location and magnitude improvement, the OBS network was able to detect hundreds of earthquakes, mostly with magnitude below Mw 3, including a swarm activity at the Molloy Deep. Our offshore observations provide further evidence of a low-velocity anomaly offshore Svalbard, at the northern tip of Knipovich ridge that was previously seen in full-waveform inversion. We conclude that even a single permanent OBS near the ridge would make a significant difference to earthquake catalogs and their interpretation.

Are bright spots always hydrocarbons? A case study in the Taranaki Basin, New Zealand

2020 ◽  
Vol 8 (4) ◽  
pp. SR45-SR51
Author(s):  
Peter Reilly ◽  
Roberto Clairmont ◽  
Heather Bedle
Keyword(s):  
New Zealand ◽  
High Amplitude ◽  
Seismic Survey ◽  
Bright Spot ◽  
Temporal Region ◽  
Cross Sectional ◽  
Seismic Amplitude ◽  
Bright Spots ◽  
Seismic Amplitudes ◽  
Seismic Anomalies

In the shallower regions of the 3D Nimitz seismic survey, there exist multiple interesting bright seismic amplitude anomalies. These anomalies, or funny looking things, occur in a confined spatial and temporal region of the seismic. They have a concave-up seismic appearance along the cross section. Bright seismic amplitudes can be a direct hydrocarbon indicator, or they can be representative of strong lithologic contrasts and/or acquisition artifacts. We have set out to investigate misinterpreted seismic anomalies along cross-sectional lines. Therefore, we apply seismic attributes to indicate that these bright spot features, which we interpret to be submarine gullies looking along time-slice intersections, can possibly be mistaken for hydrocarbon anomalies in a cross-sectional view. However, we cannot fully rule out the presence of hydrocarbons because it is common for gas sands to create similar anomalies. Previously drilled wells within the survey (Korimako-1 and Tarapunga-1) point to a lack of hydrocarbon potential in the subsurface. Although it is possible that these bright spots are due to hydrocarbon presence, we develop a more likely hypothesis: The lithology of the interfluve sediments is similar to the gully-margin drapes but differs from the gully sediment fill. Funny looking thing (FLT): Submarine gullies Seismic appearance: High-amplitude spotted features Alternative interpretations: Lithologic anomalies, gas seeps, bright spots Features with a similar appearance: Gas accumulation, sediment fills in limestone paleocaves Formation: Giant Foresets Formation Age: Pleistocene Location: Taranaki Basin, New Zealand Seismic data: Nimitz 3D (cropped volume) Analysis tools: Curvature, instantaneous frequency, and sweetness attributes; well reports

DETERMINATION OF RESERVOIR DISTRIBUTION OVER THE BLACKBACK/TERAKIHI OIL FIELD, GIPPSLAND BASIN, AUSTRALIA

1993 ◽  
Vol 33 (1) ◽  
pp. 1
Author(s):  
M.D. Gross
Keyword(s):  
Oil And Gas ◽  
Group Structure ◽  
High Amplitude ◽  
Oil Field ◽  
Seismic Survey ◽  
Seismic Attribute ◽  
Oil Accumulation ◽  
Well Control ◽  
High Impedance ◽  
Gippsland Basin

The Blackback/Terakihi oil accumulation is located within the Gippsland Basin permit Vic-P24 on the edge of the present-day continental shelf in water depths ranging from 300 to more than 600 m. Accurate structural mapping, depth conversion and delineation of the reservoir units remain as major uncertainties associated with this oil and gas accumulation. To date three wells, Hapuku-1, Blackback-1 and Terakihi-1 have been drilled on the structure and a 3D seismic survey interpreted.The top of the Latrobe Group structure is a complex erosional remnant somewhat laterally offset from a deep-seated northeast to southwest trending, faulted anticline. Most of the hydrocarbons intersected to date have been encountered within the top of the Latrobe Group closure. All three wells drilled to date have intersected oil at the top of the Latrobe Group in three markedly different reservoir units. These reservoirs range in age from Late Cretaceous to Eocene, with porosity ranging from less than 12 per cent to 26 per cent and permeability from less than 1 md to greater than 3000 md.Given the extreme variation in reservoir quality and the field's location in relatively deep water, delineating the distribution of reservoir units using all available data remains crucial.The generation of seismic attribute maps such as dip, dip azimuth and horizon amplitude slices, calibrated on existing well penetrations has played a major role in delineating a complex reservoir distribution at the top of the Latrobe Group. The calibration of high amplitude seismic events with a high impedance channel infill unit of Eocene age was supported by modelling using SIERRAR modelling software.The integration of existing well control, seismic stratigraphy and fault geometry together with seismic attribute mapping and modelling has resulted in a more tightly constrained estimate of the field reserves.

scholarly journals Recording site placement on planar silicon-based probes affects signal quality in acute neuronal recordings

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Richárd Fiáth ◽  
Domokos Meszéna ◽  
Zoltán Somogyvári ◽  
Mihály Boda ◽  
Péter Barthó ◽  
...  
Keyword(s):  
Single Unit ◽  
Brain Activity ◽  
Amplitude Distribution ◽  
High Amplitude ◽  
Neural Implants ◽  
Recording Site ◽  
Significant Difference ◽  
Planar Silicon ◽  
Silicon Based ◽  
Unit Yield

AbstractMultisite, silicon-based probes are widely used tools to record the electrical activity of neuronal populations. Several physical features of these devices are designed to improve their recording performance. Here, our goal was to investigate whether the position of recording sites on the silicon shank might affect the quality of the recorded neural signal in acute experiments. Neural recordings obtained with five different types of high-density, single-shank, planar silicon probes from anesthetized rats were analyzed. Wideband data were filtered to extract spiking activity, then the amplitude distribution of samples and quantitative properties of the recorded brain activity (single unit yield, spike amplitude and isolation distance) were compared between sites located at different positions of the silicon shank, focusing particularly on edge and center sites. Edge sites outperformed center sites: for all five probe types there was a significant difference in the signal power computed from the amplitude distributions, and edge sites recorded significantly more large amplitude samples both in the positive and negative range. Although the single unit yield was similar between site positions, the difference in spike amplitudes was noticeable in the range corresponding to high-amplitude spikes. Furthermore, the advantage of edge sites slightly decreased with decreasing shank width. Our results might aid the design of novel neural implants in enhancing their recording performance by identifying more efficient recording site placements.

scholarly journals Impact of Diagenesis on the Low Permeability Sandstone Reservoir: Case Study of the Lower Jurassic Reservoir in the Niudong Area, Northern Margin of Qaidam Basin

Minerals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 453
Author(s):  
Wenhuan Li ◽  
Tailiang Fan ◽  
Zhiqian Gao ◽  
Zhixiong Wu ◽  
Ya’nan Li ◽  
...  
Keyword(s):  
Physical Properties ◽  
Oil And Gas ◽  
Qaidam Basin ◽  
Isotope Analysis ◽  
Lower Jurassic ◽  
Low Permeability ◽  
Hydrocarbon Generation ◽  
Northern Margin ◽  
Pore Evolution ◽  
Sandstone Reservoir

The Lower Jurassic reservoir in the Niudong area of the northern margin of Qaidam Basin is a typical low permeability sandstone reservoir and an important target for oil and gas exploration in the northern margin of the Qaidam Basin. In this paper, casting thin section analysis, scanning electron microscopy, X-ray diffraction, and stable isotope analysis among other methods were used to identify the diagenetic characteristics and evolution as well as the main factors influencing reservoir quality in the study area. The predominant types of sandstone in the study area are mainly feldspathic lithic sandstone and lithic arkose, followed by feldspathic sandstone and lithic sandstone. Reservoir porosity ranges from 0.01% to 19.5% (average of 9.9%), and permeability ranges from 0.01 to 32.4 mD (average of 3.8 mD). The reservoir exhibits robust heterogeneity and its quality is mainly influenced by diagenesis. The Lower Jurassic reservoir in the study area has undergone complex diagenesis and reached the middle diagenesis stage (A–B). The quantitative analysis of pore evolution showed that the porosity loss rate caused by compaction and cementation was 69.0% and 25.7% on average, and the porosity increase via dissolution was 4.8% on average. Compaction was the main cause of the reduction in the physical property of the reservoir in the study area, while cementation and dissolution were the main causes of reservoir heterogeneity. Cementation can reduce reservoir space by filling primary intergranular pores and secondary dissolved pores via cementation such as a calcite and illite/smectite mixed layer, whereas high cement content increased the compaction resistance of particles to preserve certain primary pores. δ13C and δ18O isotopes showed that the carbonate cement in the study area was the product of hydrocarbon generation by organic matter. The study area has conditions that are conductive to strong dissolution and mainly occur in feldspar dissolution, which produces a large number of secondary pores. It is important to improve the physical properties of the reservoir. Structurally, the Niudong area is a large nose uplift structure with developed fractures, which can be used as an effective oil and gas reservoir space and migration channel. In addition, the existence of fractures provides favorable conditions for the uninterrupted entry of acid fluid into the reservoir, promoting the occurrence of dissolution, and ultimately improves the physical properties of reservoirs, which is mainly manifested in improving the reservoir permeability.

scholarly journals Multi-Year NDVI Values as Indicator of the Relationship between Spatiotemporal Vegetation Dynamics and Environmental Factors in the Qaidam Basin, China

2021 ◽  
Vol 13 (7) ◽  
pp. 1240
Author(s):  
Junpeng Lou ◽  
Guoyin Xu ◽  
Zhongjing Wang ◽  
Zhigang Yang ◽  
Sanchuan Ni
Keyword(s):  
Environmental Factors ◽  
Vegetation Dynamics ◽  
Vegetation Index ◽  
Qaidam Basin ◽  
Elevation Gradient ◽  
Practical Significance ◽  
Elevation Gradients ◽  
Relative Contribution ◽  
Significant Difference ◽  
Different Altitudes

The Qaidam Basin is a unique and complex ecosystem, wherein elevation gradients lead to high spatial heterogeneity in vegetation dynamics and responses to environmental factors. Based on the remote sensing data of Moderate Resolution Imaging Spectroradiometer (MODIS), Tropical Rainfall Measuring Mission (TRMM) and Global Land Data Assimilation System (GLDAS), we analyzed the spatiotemporal variations of vegetation dynamics and responses to precipitation, accumulative temperature (AT) and soil moisture (SM) in the Qaidam Basin from 2001 to 2016. Moreover, the contribution of those factors to vegetation dynamics at different altitudes was analyzed via an artificial neural network (ANN) model. The results indicated that the Normalized Difference Vegetation Index (NDVI) values in the growing season showed an overall upward trend, with an increased rate of 0.001/year. The values of NDVI in low-altitude areas were higher than that in high-altitude areas, and the peak values of NDVI appeared along the elevation gradient at 4400–4600 m. Thanks to the use of ANN, we were able to detect the relative contribution of various environmental factors; the relative contribution rate of AT to the NDVI dynamic was the most significant (35.17%) in the low-elevation region (< 2900 m). In the mid-elevation area (2900–3900 m), precipitation contributed 44.76% of the NDVI dynamics. When the altitude was higher than 3900 m, the relative contribution rates of AT (39.50%) and SM (38.53%) had no significant difference but were significantly higher than that of precipitation (21.97%). The results highlight that the different environmental factors have various contributions to vegetation dynamics at different altitudes, which has important theoretical and practical significance for regulating ecological processes.

Multiphase Transient Slugging Flow in Subsea Oil and Gas Production

2016 ◽  
Author(s):  
Zhenhua Zhang ◽  
Longbin Tao
Keyword(s):  
Data Analysis ◽  
Temperature Distribution ◽  
Numerical Model ◽  
Slug Flow ◽  
Field Data ◽  
Oil And Gas ◽  
Gas Production ◽  
Worst Case ◽  
Oil And Gas Production ◽  
Significant Difference

Slug flow in horizontal pipelines and riser systems in deep sea has been proved as one of the challenging flow assurance issues. Large and fluctuating gas/liquid rates can severely reduce production and, in the worst case, shut down, depressurization or damage topside equipment, such as separator, vessels and compressors. Previous studies are primarily based on experimental investigations of fluid properties with air/water as working media in considerably scaled down model pipes, and the results cannot be simply extrapolated to full scale due to the significant difference in Reynolds number and other fluid conditions. In this paper, the focus is on utilizing practical shape of pipe, working conditions and fluid data for simulation and data analysis. The study aims to investigate the transient multiphase slug flow in subsea oil and gas production based on the field data, using numerical model developed by simulator OLGA and data analysis. As the first step, cases with field data have been modelled using OLGA and validated by comparing with the results obtained using PIPESYS in steady state analysis. Then, a numerical model to predict slugging flow characteristics under transient state in pipeline and riser system was set up using multiphase flow simulator OLGA. One of the highlights of the present study is the new transient model developed by OLGA with an added capacity of newly developed thermal model programmed with MATLAB in order to represent the large variable temperature distribution of the riser in deep water condition. The slug characteristics in pipelines and temperature distribution of riser are analyzed under the different temperature gradients along the water depth. Finally, the depressurization during a shut-down and then restart procedure considering hydrate formation checking is simulated. Furthermore, slug length, pressure drop and liquid hold up in the riser are predicted under the realistic field development scenarios.

Infodemic surrounding COVID-19: Can LIS students recognize and categorize “problematic information” types on social media?

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Shamima Yesmin ◽  
S.M. Zabed Ahmed
Keyword(s):  
Social Media ◽  
Online Survey ◽  
Information Science ◽  
Wrong Answer ◽  
Student Groups ◽  
Content Type ◽  
Correct Definition ◽  
Significant Difference ◽  
Definition Of ◽  
And Task

Purpose The purpose of this paper is to investigate Library and Information Science (LIS) students’ understanding of infodemic and related terminologies and their ability to categorize COVID-19-related problematic information types using examples from social media platforms. Design/methodology/approach The participants of this study were LIS students from a public-funded university located at the south coast of Bangladesh. An online survey was conducted which, in addition to demographic and study information, asked students to identify the correct definition of infodemic and related terminologies and to categorize the COVID-related problematic social media posts based on their inherent problem characteristics. The correct answer for each definition and task question was assigned a score of “1”, whereas the wrong answer was coded as “0”. The percentages of correctness score for total and each category of definition and task-specific questions were computed. The independent sample t-test and ANOVA were run to examine the differences in total and category-specific scores between student groups. Findings The findings revealed that students’ knowledge concerning the definition of infodemic and related terminologies and the categorization of COVID-19-related problematic social media posts was poor. There was no significant difference in correctness scores between student groups in terms of gender, age and study levels. Originality/value To the best of the authors’ knowledge, this is the first time an effort was made to understand LIS students’ recognition and classification of problematic information. The findings can assist LIS departments in revising and improving the existing information literacy curriculum for students.

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