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Case Study: Saturation Evaluation with RSTPro Tool Finds Bypassed Oil and Gas Zones

Sigma and C/O logging finds 27.5 MMcf/d of gas and 997 bbl/d of oil in a North Sea well previously shut in for high water cut

Challenge: Identify bypassed hydrocarbons in a North Sea well shut in 6 years earlier because of high water cut and low pressure.

Solution: Run the RSTPro reservoir saturation tool to evaluate saturations and determine depths for shutting off existing perforations and reperforating.

Result: Identified three intervals for reperforating that are producing 27.5-MMcf/d gas, 997-bbl/d oil, and only 1.7% water.

Looking for bypassed hydrocarbons

An operator wanted to identify any bypassed hydrocarbons in a North Sea well that had been shut in because of high water cut and low pressure. The plan was to shut off the water-flushed producing zones and recomplete the new zones.

Measuring water and hydrocarbon saturations

The innovative dual-detector spectrometry system of the through-tubing RSTPro reservoir saturation tool records carbon and oxygen and Dual-Burst thermal decay time measurements in the same pass. The C/O ratio is used to determine the formation oil saturation independent of the formation water salinity. The sigma log of the thermal neutron capture cross section is used to determine water saturation behind casing. Porosity is also measured for formation evaluation.

Identifying new gas and oil zones

The well was logged with the RSTPro tool under shut-in conditions. Schlumberger petrotechnical experts conducted an integrated evaluation of the data. Formation sigma and related gas indicators were used to identify gas-bearing zones, and the C/O data were used to characterize the oil- and water-bearing zones. The source of the water was confirmed, and new potential oil and gas reservoirs were identified.

On the basis of the petrotechnical evaluation, the operator set a bridge plug to isolate the water-bearing zone and perforated three intervals using a 2 7/8-in PURE perforating system for clean perforations with deep penetrating PowerJet Omega shaped charges to perforate through any formation damage and create clean perforation tunnels.

Post intervention, the three new intervals were producing 27.5-MMcf/d gas, 997-bbl/d oil, and only 1.7% water.


Download: RST Saturation Evaluation Finds Bypassed Oil and Gas Zones (0.28 MB PDF)

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