Fluid Contacts and Reservoir Compartmentalization #1

My first experience of a truly integrated sub-surface study was the Dulang FDP project when I joined Landmark in 2005-06. It was a large team consisting of 10-15 members from different subsurface disciplines. I joined the team a bit late - Petrophysics & Geophysics interpretation was almost completed, Geomodelling was in full swing and Reservoir Engineering work just started. However, as soon as the Geologist/Reservoir Engineer started integrating interpreted logs, fluid contacts, surfaces, faults etc. with other information like production data, pressure trends, structural frame work etc., we observed several inconsistencies. For your information, Dulang field is a fairly large field with 13+ stacked reservoirs, several fault compartments and already close to 100 wells drilled by that time, if I remember correctly. Some examples are

1. inconsistency between RFT/MDT data and log interpretations

2. variation in fluid contacts within same fault-block

3. fluid contacts deeper then structural spill point

4. Fluid contacts beyond extension of faults separating blocks

5. interpreted fluid type inconsistent with production / test results

6. Multiple pressure trends within same compartment

There were several sets of one-to-one discussions between the involved disciplines, but the issues dragged on for several weeks as each member tried to defend their own interpretations. Finally the Project Manager and the Sr. Reservoir Engineer got the whole team into a large conference room, locked the doors and said to the team "you cannot leave this room unless you can get to an agreement". That got everybody's attention. For the next 2-3 days, we reviewed all the interpretations/information as a team, updated some of the interpretations and finally reached into a set of consistent, defendable and mutually agreed fluid contacts.

We identified several issues which were obvious when working as a team, but overlooked when interpreters were working on their own or discussing one-to-one.

1. Fluid contacts picked on post-production wells

2. Fluid contacts picked on tight/shale intervals

3. Fault extension reviewed and updated to honour fluid contacts

4. Depth structure reviewed and updated to honour fluid contacts

5. Well tops reviewed and updated if needed (including dividing reservoirs into sub-layers if needed)

6. Well MD to TVD conversion reviewed and updated

7. Fluid interpretation updated to honour production / test results

8. Compartments updated to honour pressure trends

More examples in my next blog.