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A D D I N G V A L U E
All Petrophysicists are NOT the same as the real examples below from the experience of our Principal Petrophysicist
illustrate. In these summaries our expertise has added significant
value to Operating Companies. In all cases, other Petrophysicists had
been involved previously, but had not recognised what was really
happening.
Oil Discovery in Recently Abandoned Well
Steve arrived at an Operating Company and was asked to take over
Petrophysical support for one of the onshore exploration teams. His
first task was to write up a Petrophysical analysis of a well that had
been abandoned 4 days before he arrived, on the advice of his
predecessor.
During the interpretation it quickly became evident that a significant
oil-bearing sand had been overlooked. Steve brought his version of the
interpretation to the attention of the Exploration Team Leader. No
action was taken until another well was drilled nearby on a separate,
but similar, structure. Here, Steve interpreted a zone similar to that
in the abandoned well to be oil-bearing. This zone was tested at a rate
in excess of 1000 bbl/d of dry oil.
Following this success, the previously abandoned well was re-drilled
and successfully put on production at a rate in excess of 1200 bbl/day
of dry oil.
Appraisal Reserves Target Met Through Petrophysical Review
Steve was asked to assist with the Operational Petrophysics during the
Appraisal of an Offshore Gas Field. The target of the appraisal was to
increase the reserves from around 0.8 to greater than 1.0 TCF to meet
an economic threshold.
Steve immediately noted that the previous Petrophysics models were
inappropriate, despite being worked on by three different
Petrophysicists with international experience. Steve implemented a more
rigorous model calibrated to core acquired in the exploration phase.
The desired 25% reserves increase was produced by this change alone!
Previously Unrecognised Gas Resource Identified
Steve was asked to look at a couple of abandoned exploration wells to
see if he could explain why gas had been tested at low rates from one
well before the hole was lost, but the up-dip redrill had flowed
nothing at all.
Steve’s initial investigation revealed that both wells were in
gas-bearing, low permeability reservoirs. The testing methodology
adopted had ensured test failure. On further investigation, Steve found
an additional five wells drilled into the same Formations in the nearby
vicinity, all of which contained previously unrecognised gas-bearing
sands.
After a lot of justification, the Operator was finally convinced to put
a Team together to investigate the potential resource. A new well
location was finally selected and a well drilled. Following completion
and fracture treatment the well was put on production at commercial gas
flow rates.
Sub-Sea Completion Disaster Averted at Final Planning Stage
On arrival at an Operating Company, Steve was placed into a Team
planning a sub-sea oil field development. The wells were scheduled to
be drilled in 3 months and the hardware had already been ordered for
the completions.
During Steve’s first attendance at the weekly Team Meeting, the
completion strategy for the two producing wells was outlined. This
strategy had been previously agreed with all the other Team members and
other contractors involved.
The wells were to be drilled at angles around 40º, before the
completion strings were run with 100 metres of TCP (Tubing Conveyed
Perforating) guns at the bottom of the tubing string. The wells were to
be suspended unperforated until they were hooked up. Following hook-up,
the guns would be fired, dropping into a long rat-hole below the
tailpipe after firing, allowing the wells to go straight onto
production.
After hearing the briefing, Steve asked for clarification on the casing
and gun sizes. It was confirmed that 100 metres of 4 inch TCP guns
would be used “to get good penetration into the sandstone”.
These guns would be run inside an industry standard 4 ½ inch
liner.
Steve then asked if anyone in the room had ever seen a perforating gun
after it had been fired? Nobody had, and they wondered why he asked.
They were very surprised when Steve pointed out how unlikely it was
that the 4 inch TCP guns would ever drop to the bottom of the hole
after firing. The clearance between the guns and the liner was too
small at 40º to cope with any gun buckling or perforation burr.
The guns would almost certainly not fall to the bottom of the hole,
leaving a downhole choke in place!
Steve and the completion specialist were detailed to follow up with the
perforating contractor whether or not the “downhole choke”
was likely to be a problem. The perforating contractor contacted his
Head Office specialists, receiving a reply in very short order that the
planned perforating strategy was a very bad idea.
The wells were successfully completed with 2 7/8 inch guns when drilled.
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