Well Cores & Logs

Example of a cylindrical whole rock core

Chris Eisinger and Phyllis Scott (CGS) logging Dakota core at USGS warehouse.

Top: Example of a cylindrical whole rock core. Lower: Detailed visual analysis of slabbed cores can provide valuable insight regarding the subsurface geology.

Well cores are cylindrical rock samples collected as part of the drilling process. Cores provide valuable insight into the porosity and permeability, among other characteristics, of the rocks that are being drilled. Several types of cores can be recovered from the well, including full-diameter cores, oriented cores, native state cores and sidewall cores.

Where can I find well cores from Colorado wells?

While there is no state-maintained repository for Colorado-specific well cores, there are several options for finding cores.

First, try visiting the Petroleum Technology Transfer Council’s (PTTC) core locator website. This service includes Colorado cores that have been put in many of the largest repositories.

Perhaps, most important locally is the US Geological Survey’s Core Research Facility located at the Denver Federal Center. This facility is one of the largest core repositories in the US, and contains many cores from Colorado, as well as throughout the Rocky Mountain region and beyond.

Another option is the Core Research Center managed by the Texas Bureau of Economic Geology. Their collection (located at three separated facilities in Austin, Midland, and Houston) includes well samples from Colorado and across the US.

Tony Troutman, exploration geologist, hosts a dated (2009) but relatively comprehensive list of the major core repositories in the US.

Wireline Logs

Logs provide critical information for evaluating oil and gas reservoir potential, as well as giving engineers and geologists a better understanding of what to expect during production operations. From the Schlumberger Oilfield Glossary, a wireline log can be defined as: A continuous measurement of formation properties with electrically powered instruments to infer properties and make decisions about drilling and production operations. The record of the measurements, typically a long strip of paper, is also called a log. Measurements include electrical properties (resistivity and conductivity at various frequencies), sonic properties, active and passive nuclear measurements, dimensional measurements of the wellbore, formation fluid sampling, formation pressure measurement, wireline-conveyed sidewall coring tools, and others.

Wireline logs from three wells in northwest Colorado

Wireline logs from three wells in northwest Colorado.

Wireline logs rely on physical measurements to be made by instruments lowered into the borehole on a cable (wire). Once the zone of interest is reached, the actual measurements are traditionally recorded as the instrument is pulled up towards the surface. There are many types of sophisticated wireline logging tools, including newer tools that allow for logging to occur while drilling (LWD). For a good overview of the various tool classes, go here.

Where can I find wireline logs for Colorado wells?

Publicly available wireline logs (both raster and LAS format) are available through the Colorado Oil and Gas Conservation Commission. Both a direct database query or map search utility are available. Additionally, there are commercial vendors that maintain raster and digital log databases for purchase.