A Shallow Gas Research Program

Grinrod, M.; Haaland, O.; Ellingsen, B.

doi:10.2523/17256-ms

Cited by 7 publications

(1 citation statement)

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“…Blowouts from drilling into a pressurised gas pocket are of particular concern, and the West Vanguard blowout that occurred at 523‐m RKB on the Halten Bank, Norwegian Sea serves as a prime example of the tragic consequences (human, economic, and environmental) that can arise from such an event (Nørstebø et al . ; Grinrod, Haaland and Ellingsen ).…”

Section: Introductionmentioning

confidence: 99%

Tuning, interference and false shallow gas signatures in geohazard interpretations: beyond the rule

Barrett

Huws

Booth

et al. 2017

Near Surface Geophysics

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Shallow gas presents a significant geohazard for drilling operations, with implications for costly well deviations and inherent blowout risks. The archetypal seismic signature of shallow gas—a “bright spot”—can be falsely induced by tuning, whereby reflections from closely separated horizons stack and constructively interfere. According to established guidelines, maximum constructive interference is typically expected where horizons are separated by one‐quarter wavelength (λ/4) of the seismic wavelet. Here, we test the circumstances in which false gas signatures can be induced from tuning and the conditions in which the “λ/4” guidelines for interference become problematic. We simulate normal‐incidence seismic data for a variety of reflectivity models, incorporating different contrasts in reflectivity magnitude and polarity. We simulate acoustic impedance by supplying initial geological parameters to Gassmann’s rock physics equations, allowing bulk density and compressional (P‐) wave velocity to vary between 1200–2100 kg/m3 and 1460–1670 m/s, respectively, for non‐gassy sediments and 1160 kg/m3 and 170–200 m/s for gassy sediments. Tuning is considered for a Ricker wavelet source pulse, having both peak frequency and effective bandwidth of 60 Hz. Tuning effects are able to mask a gas pocket, corresponding to a “false negative” signature that represents a significant hazard for drilling operations. Furthermore, the widely adopted λ/4 assumption for constructive interference is not always valid as the brightest seismic responses can appear for thicker (<“λ/2”) and thinner (>“λ/16”) beds, depending upon the stratigraphy. Similar observations are made both qualitatively and quantitatively for real seismic responses, in which reflections from a series of dipping clinoforms interfere with those from an overlying unconformity. We conclude that greater attention should be paid to the interpretation of shallow gas risk; specifically, the effect of reflector geometries should not be overlooked as a means of producing or masking seismic amplitudes that could be indicative of a hazardous gas accumulation.

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Section: Introductionmentioning

confidence: 99%

Tuning, interference and false shallow gas signatures in geohazard interpretations: beyond the rule

Barrett

Huws

Booth

et al. 2017

Near Surface Geophysics

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A Review on Offshore Concepts and Feasbility Study Considerations

Maddahi

Mortazavi²

2011

SPE Asia Pacific Oil and Gas Conference and Exhibition

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There is no doubt that choosing the excellent technology and operation is one of the keys to achieve sustainable global energy. With the quick advancement in the subsea technology and offshore industry and its influence on the global oil and gas production through the past three decades, an update working knowledge of engaged offshore facilities around the world seems to be essential for a successful petroleum field development. Selection of the most appropriate equipment and process through the early exploitation study stages of developing an offshore petroleum reservoir can determine the right facilities for delivering the greatest value. The current paper gives an overview of characteristics, and features of offshore production facilities, their advantages and disadvantages according to the most common offshore system selection and feasibility studies considerations. It has been tried to point out the most important criteria of the related Issues and concerns during a process and facilities selection for a potential case of installing the subsea completion as well as proposing processes to help in selection of the right concept. Major considerations in the process and facility selection for a petroleum field, such as shore distance, drilling and well intervention, topside weight, utilities, accessibility, regional influences, financial and HSE considerations, and particularly water depth and well count, as well as their influences on the final decision have also been explored. The review also introduces common components of a subsea completion system such as wellheads, manifolds, flowlines and risers, connection systems, control systems and umbilicals, installation tooling, and then it makes a comparison between different types of Xmas trees as well as various well arrangements. Finally, the paper summarizes the subsea development phases for establishing the right concept.

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The Drilling Engineering for Subsea Development Wells

King

1989

SPE/IADC Drilling Conference

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Twelve subsea development wells have been drilled in block 9/13 in the North Sea. The early completions were of exploration or appraisal wells, later wells were planned for development. The experience has led to a drilling engineering strategy for planning all wells to ensure that the maximum benefit from each well can be achieved. This involves: grouping the wells together to minimise surface locations and flowline routes; designing all wells to be suitable for a subsea completion; and specifying a rig that can be used for all phases of a subsea development. Introduction Since well 9/13a - 1 discovered the Beryl field in block 9/13, 215 miles (346km) north-east of Aberdeen, forty two more subsea wells have been drilled in the block, of which twelve have been completed. The early wells were for the appraisal of the original discoveries and exploration in other areas of the block. The success of the discovery resulted in the installation of two combined drilling and production platforms. The Beryl 'A', a three legged concrete platform with storage capacity in the base for more than 1bn bbls of oil, was installed in 1976. In 1983 the Beryl 'B', a steel jacket was installed with an oil export line to the 'A' platform. Oil export from the block has always been by tanker loading from a Single Point Mooring. In 1986 the Ness field was discovered by well 9/13a - 28 and the field came on stream with a subsea development in 1987 (Figure 1). From the very first well, the possibility of re-using the exploration and appraisal wells for subsea production via the platform facilities was always an option and wells which had identified significant hydrocarbon potential were suspended, pending completion. The first subsea well to be drilled as a development well was 9/13a-20. Since then several more subsea development wells have been drilled. This pattern of subsea developments using the process and export facilities of a platform is common to oil production from the North Sea.

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A Shallow Gas Research Program

Cited by 7 publications

References 0 publications

Tuning, interference and false shallow gas signatures in geohazard interpretations: beyond the rule

Tuning, interference and false shallow gas signatures in geohazard interpretations: beyond the rule

A Review on Offshore Concepts and Feasbility Study Considerations

The Drilling Engineering for Subsea Development Wells

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