Case Study: Petrophysical Evaluation Reduces Uncertainty in Large-Diameter, Washed Out Well

Formation-density and behind-casing analysis provide Wintershall reliable data from 12.25-in-diameter carbonate well, Libya

Challenge: Reduce uncertainty in large-diameter, 9.625-in-casing carbonate well by measuring and interpreting accurate formation density and additional petrophysical data.

Solution: Collaborate with Schlumberger petrotechnical experts to gather cased hole formation density data for analysis with GeoFrame reservoir characterization software.

Result: Reliably matched logging value and response from the nearby wells in the same area, reducing uncertainty of volumetric openhole evaluation analysis through accurate determination of porosity and lithology.

Quantitatively evaluate carbonate behind thick cement

Wintershall Libya was operating in the eastern Sirte basin and wanted to perform a complete formation evaluation for one of its wells in the As-Sarah field. Although density measurement was included as a basic service in the openhole logging program, the large-diameter wellbore’s bad hole condition required the installation of 9.625-in casing, forcing logging acquisition to be in cased hole.

Determine and model formation properties with expert log interpretation

Schlumberger petrotechnical experts worked with the Wintershall petrophysics team to obtain accurate formation density data behind the 9.625-in casing and thick cement section. Schlumberger proposed using a three-detector system to make a formation density measurement that corrected for the large casing size. Density, weight, thickness, and quality served as inputs to obtain accurate, reliable data. The formation density data was plugged into GeoFrame software for petrophysical interpretation. Processing the data took only 24 hours, and results were delivered to Wintershall directly.

Increase confidence in decisions with dependable data

With the cased hole formation density log and interpretation, Wintershall was able to perform well-to-well correlation, reducing uncertainty of volumetric openhole evaluation with accurate porosity and detailed lithology results. Additionally, Wintershall generated a synthetic seismogram along with the sonic log, which was used to confirm the seismic reflectors on both the surface seismic survey and the vertical seismic profile. Schlumberger and Wintershall petrophysicists reviewed the reprocessed data and compared it with the data of openhole logs from nearby wells, confirming excellent match and reliability.

Download: Petrophysical Evaluation Reduces Uncertainty in Large-Diameter, Washed Out Well (0.25 MB PDF)

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Density Log Interpretation Enables Interwell Correlation

Log summarizing the CHFD service data.
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"It was difficult to log the bulk density of the 12.25-in section because of bad-hole effects that included borehole instability and total fluid loss. For the first time in this area, we were able to get more reliable and accurate density log data in a large hole size with excellent reprocessing results."
Wesam Ben Mansour
Senior Petrophysicist
Wintershall Libya