Petrophysical Modeling of the Marble Falls Formation in the Fort Worth Basin: A Case Study of Bringing Legacy Wireline Log Data into the Modern Era

Mike Mullen¹, Craig Adams², Ulysses Hargrove², and Beau Berend²

¹Newark E&P Operating

Abstract

In most mature basins, one is blessed or cursed with an abundance of wireline log data. The vintage of these data might range from the 1930s to present day and may include a dozen service providers with a variety of quality and calibration standards. One constant in the wireline service business is that tool technology is ever evolving and tool response to the same rock often changes with time, calibration standards and service providers. To be able to use these legacy data in concert with modern data to explore for and exploit new plays in mature basins, a systematic workflow was developed to insure that the analyses compare apples to apples.

The process used in developing the Marble Falls in the Fort Worth Basin started with a few encouraging modern well completions to verify the play concept. The next step was to scan the legacy data and construct maps of the reservoir characteristics to guide the land acquisition and drilling programs. The early mapping used the legacy wireline log data, which posed a problem. Legacy wireline log data aren't necessarily 'wrong', but quite often they exhibit different measurement responses or include different log suites than those of modern data sets. This could have significant effects on regional mapping of the resource.

Using modern log data as control points, the legacy data were 'normalized' to reflect the same measurement sensitivity as that found in the modern data. Using the modern dipole sonic logs as a training set, compressional slowness and fast and slow shear wave slowness were estimated for all the wells missing these measurements. Finally, natural fracture frequency was derived from modern image logs and used as a training set to generate a synthetic fracture frequency curve for all wells without image logs, and this was used to map out the fracture 'sweet spots'.

With the legacy and modern log data reflecting the same tool sensitivity, a core-based petrophysical model was derived so that a single set of analysis parameters were used for all wells within the study area. This insured consistency of modeling parameters from well to well and a consistency of the reservoir volumetric results from well to well. The reservoir volumetric results were then mapped and used to help guide development of the Marble Falls into a new successful play in a mature basin.

AAPG Datapages/Search and Discovery Article #90190©AAPG Southwest Section Annual Convention, Midland, Texas, May 11-14, 2014