Using diving waves for detecting shallow overburden gas layers

Geophysics ◽  
2021 ◽  
pp. 1-53
Author(s):  
Martin Landrø ◽  
Bjarte Foseide ◽  
Izzie Yi Liu
Keyword(s):  
Seismic Data ◽  
Gas Flow ◽  
Time Shift ◽  
Wave Analysis ◽  
Shallow Gas ◽  
Shallow Subsurface ◽  
Shift Analysis ◽  
Gas Layer ◽  
Simple Equations ◽  
3D Seismic Data

We propose to use simple time shift analysis of diving waves to analyze shallow gas layers in a sedimentary overburden. By using simple equations for how the traveltime will change if a thin sand layer is charged by gas in a localized and constrained region, we show that such variations can be used to map and quantify the thickness of the gas layer. We use conventional 3D seismic data acquired close to a well where an unintended underground gas flow occurred in 1989. Raw seismic data are used as input and timeshifts are estimated for constant offsets for events that are interpreted as being predominantly diving waves. By assuming that the very shallow subsurface has a constant velocity gradient of 0.5 s-1, we find diving wave time shifts that fits an average thickness of the gas layer of approximately 3-4 m. This is the minimum gas thickness since it is assumed that the time shift analysis captures both the diving wave hitting the top and the base of the gas layer (sufficient dense offset sampling is important to achieve this). The outline and circumference of the close to circular gas anomaly around the well obtained by the diving wave analysis is confirmed by the 3D reflection mapping of the same anomaly.

The Vale of Pickering gas fields: Kirby Misperton, Malton, Marishes and Pickering, North Yorkshire, UK Onshore

2020 ◽  
Vol 52 (1) ◽  
pp. 82-93 ◽  
Author(s):  
D. Harrison ◽  
M. Haarhoff ◽  
M. Heath-Clarke ◽  
W. Hodgson ◽  
F. Hughes ◽  
...  
Keyword(s):  
Seismic Data ◽  
Gas Flow ◽  
Lower Carboniferous ◽  
Gas Recovery ◽  
Water Influx ◽  
Water Breakthrough ◽  
Artificial Lift ◽  
Cumulative Production ◽  
Gas Fields ◽  
3D Seismic Data

AbstractThe Vale of Pickering gas fields were discovered over a 20-year period. The development scheme was aimed to deliver 9.3 MMscfd gas to the Knapton Power Station nearby. Cumulative production is 30.3 bcf from an estimated 172 bcf gas initially in place. The gas fields comprise a series of low relief structures at depths around 5000 ft true depth subsea. The primary reservoir is Zechstein Group dolomitized and fractured carbonates of the Permian Kirkham Abbey Formation with average reservoir quality ranges of 12–13% porosity and 0.5–1.5 mD permeability. Secondary reservoirs exist in Carboniferous sandstones directly below the Base Permian Unconformity. The gas is sourced from Lower Carboniferous shales. The fields were discovered using 2D seismic data and subsequent 3D seismic data have been merged to form a 260 km2 dataset. Zechstein production has been limited by early water breakthrough. Artificial lift is planned to enhance the gas flow rate on the Pickering Field and anticipated water influx will be re-injected. If this enhanced gas recovery scheme is successful it can be applied to the other fields. Plans to hydraulically fracture a number of zones in the Carboniferous Lower Bowland Section are in progress.

Planning a drilling campaign in a petroleum province using high resolution 3D seismic data – IODP proposal 909

2020 ◽  
Author(s):  
David Cox ◽  
Andrew M. W. Newton ◽  
Paul C. Knutz ◽  
Mads Huuse
Keyword(s):  
High Resolution ◽  
Gas Hydrate ◽  
Seismic Data ◽  
Large Scale ◽  
Greenland Ice Sheet ◽  
Hydrocarbon Exploration ◽  
3D Seismic ◽  
Free Gas ◽  
Shallow Subsurface ◽  
3D Seismic Data

<p>A drilling hazard assessment has been completed for a large area of the NW Greenland-Baffin Bay continental shelf. This assessment was in relation to International Ocean Discovery Program (IODP) proposal 909 that aims to drill several sites across the shelf in an attempt to better understand the evolution and variability of the northern Greenland Ice Sheet. The assessment utilised high quality and extensive 3D seismic data that were acquired during recent hydrocarbon exploration interest in the area – a fact that highlights the risk of drilling in a petroleum province and therefore, the importance of this assessment with regards to safety.</p><p>Scattered seismic anomalies are observed within the Cenozoic sedimentary succession covering the rift basins of the Melville Bay region. These features, potentially representing the presence of free gas or gas-rich fluids, vary in nature from isolated anomalies, fault flags, stacked fluid flow features and canyons; all of which pose a significant drilling risk and were actively avoided during site selection. In areas above the Melville Bay Ridge – a feature that dominates the structure of this area – free gas is also observed trapped beneath extensive gas hydrate deposits, identified via a spectacularly imaged bottom simulating reflector marking the base of the gas hydrate stability zone. The location of the hydrate deposits, and the free gas beneath, are likely controlled by a complicated migration history, due to large scale rift-related faulting and migration along sandy aquifer horizons. In other areas, gas is interpreted to have reached the shallow subsurface due to secondary leakage from a deeper gas reservoir on the ridge crest.</p><p>It is clear that hydrocarbon related hazards within this area are varied and abundant, making it a more challenging location to select sites for an IODP drilling campaign. However, due to the extensive coverage and high resolution (up to 11 m vertical resolution (45 Hz at 2.0 km/s velocity) of the 3D seismic data available, as well as the use of recently acquired ultra-high resolution site survey lines, these features can be accurately imaged and confidently mapped. This allowed for the development of a detailed understanding of the character and distribution of fluids within the shallow subsurface, and the use of this knowledge to select site localities that maximise the potential for drilling to be completed safely and successfully if proposal 909 were to be executed.</p>

Identifying shallow gas zones by using seismic attributes, offshore Vietnam

2020 ◽  
Vol 8 (1) ◽  
pp. T67-T76
Author(s):  
Anh Thi Van Ngo ◽  
Angus John Ferguson
Keyword(s):  
Seismic Data ◽  
High Amplitude ◽  
Seismic Attributes ◽  
Offshore Drilling ◽  
Shallow Gas ◽  
Low Frequencies ◽  
Before And After ◽  
Well Log Analysis ◽  
Push Down ◽  
3D Seismic Data

Shallow gas zones are a major concern in offshore drilling because of their potential to quickly cause kicks or blowouts. Shallow gas hazards are identified by using a series of seismic attributes. We have combined seismic data analysis and well-log analysis to identify the location and distribution of shallow gas layers. These shallow gas zones are formed during a large influx of gas due to a blowout well. The blowout well is located in the Nam Con Son Basin, offshore Vietnam. The seismic data acquired before and after the blowout record the changes in the shallow gas location. We compare seismic data without gas effects to data affected by gas after the blowout. The changes of reflectors between 2D seismic data (preblowout well) and 3D seismic data (postblowout well) are analyzed by using seismic attributes. The shallow gas is recognized in seismic data based on several criteria such as the push-down effect that demonstrated the delay in traveltime throughout the slower zone, high amplitude with negative phase reflection at the top of shallow gas layers, and acoustic blanking from wave scattering and amplitude attenuation. Geobodies mapped are associated with shallow gas zones by merging seismic attributes to identify zones that are a combination of strong amplitudes and low frequencies. The attributes that identify known shallow gas anomalies are also applied to the entire seismic volume for identification of shallow gas hazards.

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