Schlumberger

Case Study: Identify Gas and Fluid Contacts for Recompletion that Increases Oil Production by 40%

RSTPro Reservoir Saturation Measurements Accurately Delineate Gas-Bearing Zones and Fluid Contacts in East Texas

Challenge: Confirm the position of the gas cap in an East Texas well to avoid gas or water production through the original perforations.

Solution: Run the RSTPro reservoir saturation tool to calculate a weighted inelastic ratio (WINR) from inelastic and capture data that provides a fast, accurate method for evaluating gas zones and identifying fluid contacts.

Result: Based on the interpretation of the gas and fluid contacts, added perforations that increased production by 40%.

Diagnose production decline

Suspecting that the gas cap had expanded into the upper producing zone, the operator of an East Texas well wanted to recomplete to avoid gas or water production through the original perforations at X,X84 to X,X88 ft.

Identify gas zones and fluid contacts

The well was logged with the RSTPro tool in sigma mode, and the WINR curve was computed from the detector count rates. Changes in porosity and lithology cause changes in the capture count rate similar to those that occur in gas. The inelastic count rate at the far detector is sensitive to gas but relatively insensitive to lithology and liquid-filled porosity. Movement of the WINR curve by four or more divisions from the shale baseline typically indicates that formation gas is present. Borehole gas shifts the overall baseline. As shown on the log, the WINR increases by at least 10 divisions above the baseline level in the gas cap from X,X38 to X,X52 ft.

Precisely target perforations

With the RSTPro tool’s log showing that the gas cap had remained in place near the original gas/oil contact at X,X52 ft, the operator added perforations from X,X55 to X,X58 ft. Oil production subsequently increased 40%.


Download: Identify Gas and Fluid Contacts for Recompletion (0.13 MB PDF)

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