Case Study: ConocoPhillips (UK) Ltd Uses Wellsite Analysis To Prevent H2S Damage

Quicksilver Probe focused extraction acquires representative, uncontaminated fluids for rapidly evolving logging program

Challenge: Collect fluids from newly discovered secondary reservoir in a challenging North Sea well: high pressure, high temperature (HPHT); drilled with oil-base mud; and sticky hole conditions.

Solution: Conduct PVT Express onsite well fluid analysis service of high-purity samples obtained using Quicksilver Probe focused fluid extraction.

Result: Identify layers with high concentrations of H2S to exclude from perforating and prevent damage to the production tubing and facilities.

HPHT fluid collection challenges

When a ConocoPhillips (UK) Ltd HPHT well encountered an unanticipated secondary reservoir above its primary target, the logging program was immediately modified to include fluid sampling in the newly discovered zones. Obtaining representative samples in this UK North Sea well was considered challenging—oil-base mud was being used, and wells in the area were prone to sticky hole conditions resulting from the combined effects of depth, filtercake properties, hydrostatic overbalance, and wellbore tortuosity.

Onsite analysis of high-purity samples

Despite the challenging conditions, fluid acquisition by Quicksilver Probe focused fluid extraction went smoothly in the first sand, collecting high-purity oil for sampling. PVT Express onsite well fluid analysis service identified an unexpected 600- to 900-ug/g H2S in samples from that shallowest sand layer, and additional tool runs were scheduled to more closely investigate the other unexplored layers by extracting formation fluid for sampling and analysis. Subsequent onshore laboratory analysis of the collected oil samples confirmed their purity, finding only 1% contamination.

Costly damage prevented

Subsequent completion of the well perforated only the layers with lower H2S levels that were compatible with the tubing metallurgy. Without the uncontaminated fluids obtained by Quicksilver Probe extraction as part of the rapidly evolving logging program, the high concentrations of H2S from the secondary reservoir would have damaged the production tubing and entered the production facility. Mitigation would have required shutting in production and performing a costly well workover to identify and shut off the H2S zone.

Download: ConocoPhillips (UK) Ltd Prevents H2S Damage (0.10 MB PDF)

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