Adaptive methods for processing and interpretation of an underground blowout

• Author / Creator

  Dinh, Hung Nho

• In reservoir management, seismic surveillance is crucial to maximize the value of the field. It is not only useful in revealing the current reservoir situation, but also in managing future risks. In a typical seismic monitoring project, repeated data acquisition and processing are required for later quantitative analyses. With legacy data, time-lapse (4D) examination is more complex because the data acquisition is designed without the 4D application in mind.This thesis focuses on methods for processing and interpretation of a 1989 underground blowout development in the North Sea area where gas has charged into two main shallow sand layers. Efforts to study gas migration extent and changes in pressure and saturation in the two recipients were made. However, due to legacy data repeatability problems (differences in seismic acquisition and processing), a long-term blowout development investigation faced limitations in resolving 4D signals and addressing in-situ condition changes. The objectives of this study are to find a sensible strategy to process the time-lapse data, and to analyze the blowout development using 4D attenuation attribute.To increase legacy data repeatability, different seismic processing techniques are tested and compared. The following objectives are met: compensate for the acquisition feathering effects by regularization and rebinning; remove multiples by combining the predictive deconvolution and the surface related multiple elimination techniques; and correct for residual signal differences by matching the waveform and time arrivals. I also aim to preserve the seismic amplitude spectrum to evaluate attenuation changes better. The proposed strategy has created much higher quality 4D images and interpretable attributes.I then establish a complete inversion workflow to solve for changes in pore pressure and gas saturation. I find that a combination of the random patchy saturation model and the pore space stiffness model is suitable to forward model 4D attributes. I also show that a grid-search inversion scheme is successful to obtain reservoir condition changes from real time-lapse measurements. The grid-search method is also an effective approach for quality control and visual uncertainty analysis.My results provide new details about the sand conditions at different times as well as the effects of different geological structures on light gas movement. Based on the inverted pressure, I find out that gas was spreading slowly in both sand layers and that the blowout source may have stopped early. These findings are valuable to understand the blowout development and are helpful for further reservoir management.

• Subjects / Keywords

  • time lapse
  • 4D
  • blowout
  • time-lapse
  • attenuation

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-d8g4-4f13

• License

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