Pressure and Fluid Contacts · Module P4
Contacts from gradients
Two fitted gradient lines meet at the depth where the fluids are in pressure balance. This module derives that depth, separates the free water level from the oil-water contact seen on logs, puts an interval on each contact, shows how sensitive a crossing is to small pressure and gradient errors, and writes the contacts back to the well and its zones.
- Level
- Intermediate
- Position
- Module 4 of 8
- Video
- About 20 minutes, narrated
- Format
- Narrated video lesson with captions and slide reading view; with the certified option, a quiz whose pass unlocks the next module.
What the module covers
- The intersection of two gradient lines
- Gas-oil contact and free water level
- Free water level versus the log oil-water contact
- The uncertainty of a contact depth
- Sensitivity to pressure offsets and gradient errors
- Writing contacts back to the log and the zones
Learning outcomes
After the module you should be able to:
- Place a contact with its interval and its name, and state its effect on the case.
- Compute a contact depth from two gradient lines by hand
- Explain why the free water level sits below the oil-water contact seen on logs
A short preview
Write each line as pressure equals gradient times depth plus an intercept, and the contact is where the two pressures agree: depth equals the difference in intercepts divided by the difference in gradients. With oil at 0.32 psi/ft and water at 0.45, the slopes differ by only 0.13 psi/ft, so a 2 psi error in one line moves the crossing about 15 feet. That shallow angle is why a contact needs an interval, and why one doubtful test near the crossing deserves a decision of its own.
Who it is for
Petrophysicists, reservoir engineers and geoscientists who screen formation pressure tests, pick fluid contacts and carry them into volumes for exploration, appraisal and development decisions.
Prerequisites: None required; working familiarity with well logs and volumetrics helps. The hands-on steps use the Pressure Analysis panel in Formation Evaluation.
Take the module in the Learning Hub
Pressure and Fluid Contacts: Specialty course, sold separately: eight modules that turn a formation tester report into fluid contacts you can defend, from screened tests and gradients to capillary entry height and a contact range in the volume. The lesson opens in the Learning Hub once the track is purchased; graded quizzes and the certificate come with the certified option.