Application of Pressure Transient Analysis and 4D Seismic in Evaluating and Quantifying Compaction in a Deepwater Reservoir
- FNU Suleen (Chevron) | Shauna Oppert (Chevron) | Usman Lari (Chevron) | Adachi Jose (Chevron)
- Document ID
- Society of Petroleum Engineers
- SPE Western Regional Meeting, 23-26 April, San Jose, California, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. Society of Petroleum Engineers
- Integration, reservoir characterization, Compaction,Pressure Transient Analysis, 4D seismic
- 0 in the last 30 days
- 71 since 2007
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An integrated approach involving Pressure Transient Analysis (PTA) and quantitative interpretation of time lapse seismic (4D) was developed to estimate production-induced compaction in a deep-water Gulf of Mexico reservoir. The integration of both engineering and geophysical technologies is a robust approach that aims to increase the accuracy and confidence in reservoir characterization. Multiple buildups were extracted and analyzed from the flowing history of the well. Since the well was equipped with a permanent downhole gauge, good quality extended duration buildups were available for analysis. The buildups were studied using analytical pressure transient models. The well was nearly horizontal with oil, water and gas flows and the effects on permeability due to compaction were isolated from the multiphase flow effects. 4D seismic interpretations were used to estimate the temporal strain changes in the shales above the depleted sands. A relationship between shale velocity change and strain change in the reservoir was used to infer the amount of compaction observed on the 4D seismic. The interpretations indicated relatively high rates of compaction at the reservoir depths and dilation in the shales above and below. The findings were used to quantify the level of compaction in terms of porosity change in the reservoir. Sequential analysis of historical buildups integrated with 4D seismic interpretations revealed that the reservoir absolute permeability had declined significantly due to compaction. Most of this decline could be attributed to a production event after which all the buildups indicated reduced permeability level. This suggested a plastic deformation in the rocks and a study of the pressure and rate history suggested that this deformation could be associated with a sudden decrease in the flowing bottom hole pressure around the production event causing an increase in drawdown. Using the porosity-permeability correlations, a 1-2 p.u. change in porosity was estimated. The quantification of the change in porosity and permeability due to sudden increase in pressure drawdowns can be used to help guide operational decisions, where compaction is a significant concern.
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