Pressures on the Ogbon-1 Well
Learning objectives
- Read a saturation log and an RFT survey together on one well
- Find the free-water level where the oil and water gradients cross
- Read the oil and water densities from the gradient slopes
- Place the log contact above the FWL by the capillary transition
The Chapter on One Well
The pressure story comes together on the Ogbon-1 reservoir, two tracks against one depth axis across the oil-water contact. The water-saturation log shows clean oil above, a capillary transition, and full water below. Beside it the RFT survey gives an oil leg and a water leg, and where their gradients cross is the free-water level.
Two Answers, One Contact
The two tracks answer the same question independently. The gradients read the fluid densities straight off their slopes, about 0.80 and 1.05 g/cc, and cross at the FWL, the datum where capillary pressure is zero. The log contact, where oil first appears, sits some thirty feet above it, the height of the capillary transition. Neither view alone is the whole truth: the pressures give the datum, the logs give the transition, and together they pin the contact.
Why Pressures Finish the Job
Everything earlier in the course read the rock at the wellbore, one foot at a time. Pressures read the connected fluid system across the whole interval, so they fix the datum, test for seals, and cross-check every contact the logs proposed. That is why a formation-evaluation job is not done until the pressures are in, and why this chapter sits at the end of the interpretation chain.
References
- Dake, L. P. (1978). Fundamentals of Reservoir Engineering. Elsevier.
- Schlumberger (2006). Fundamentals of Formation Testing. Schlumberger.