North Sea Viking Graben Pressure Study: Overpressure and fluid flow issues in a mature basin
The pressures in the Jurassic rocks in the North Sea Viking Graben are greatest in the centre of the basin where burial depths are deepest, and large portions of this prospective deep area remain undrilled. High overpressures create drilling difficulties and increase exploration costs. They are also a significant factor in hydrocarbon migration and trapping, with the highest overpressures creating breached traps. Where drilled and pressure tested, the Jurassic strata are heavily compartmentalized by faulting, although faults appear not to uniformly seal across the basin. At shallower stratigraphic levels, overpressure occurs more locally e.g. within some Cenozoic strata, for example in the East Shetland Basin, where pressure gradients are lower.
Preliminary investigation of the comprehensive IHS Pressure Database from a small region of the North Sea Viking Graben reveals many interesting trends worthy of further detailed examination. The dataset includes direct fluid pressures (RFTs, MDTs) plus Leak-Off data, Lost Circulations and Mud Weights for most wells. The study already has access to 1242 wells out of a total 1605 released wells, providing minimum 80% coverage for the proposed study area (see Table below). Every effort will be made to add all key wells which would impact the study conclusions.
| Released Wells | IHS Database | A | B | C | |
|---|---|---|---|---|---|
| UK | 972 | 745 | 650 | 62 | 33 |
| Norway | 633 | 497 | 386 | 77 | 34 |
A: Formation pressure data
B: Fracture pressure data
C: Mud pressure data only
All categories may include supplementary pressure data.
With the intent of improving safety and drilling success in the future, aiding well planning and minimizing exploration risk, this proposed pressure study will expand on preliminary observations that include:
- Controls on pressure compartments/cells
- Pressure prediction with high temperature and mixed lithologies
- Pressure reversals and lateral drainage
- Hydrocarbon column above minimum LOP trend vs. seal capacity
For further details of the workflow, case studies and deliverables please open the PDF below.
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