Advanced Analysis of Magnetic Resonance Finds Laminated Pay, Eagle Ford Shale

Published: 10/26/2011

Blue hero texture

Conventionally undifferentiated shales

Standard log suites, which were developed for conventional reservoirs, characterize the Eagle Ford shale play as a uniform matrix. Analysis of logs with this conventional resolution cannot easily find where the best potential for oil production may occur.

Fifty-burst magnetic resonance application and high-resolution density

Magnetic resonance logging has long been applied to discern moveable from nonmoveable fluids regardless of the matrix, which is of great utility in clay-bearing formations. The new 50-burst application improves the statistics for the smallest pores by enabling the collection of more data by an advanced prepolarizing magnetic resonance tool. The result is a 6-in or greater resolution of the clay-bound micropore region of the rock.

The TLD tool uses three detectors to obtain a high-resolution 8-in density output. The TLD detector with 2-in resolution is normally applied to correct for minor wellbore changes resulting from the hole condition and mudcake. In the Eagle Ford the matrix is primarily carbonate and the well-bores are typically smooth. This logging environment allows use of the 2-in detector as a stand-alone porosity device to improve the visibility and reliability of the TLD curves.

Visible laminated pay

The Eagle Ford is highly laminated with thin laminations. Run with a conventional logging suite, the 8-in-resolution density cannot differentiate laminations with substantial porosity. However, logging analysis combining the 50-burst magnetic resonance application and high-resolution TLD readily identifies laminated pay by differentiating very small pores, micropores, and poten-tially oil-bearing matrix. Standard-resolution analysis presents only an average of the matrix, which cannot discriminate laminations.

Graph: Advanced Analysis of Magnetic Resonance Finds Laminated Pay, Eagle Ford Shale
Track 3 overlays the standard-resolution density with the 8-in and 2-in curves. The resolution of the 2-in curve is consistent with the enhanced image curve in Track 4. The 2-in-resolution density shows higher porosity (circled) along certain layers that is as much as 5-pu higher than standard resolution. In the same inter-vals, the 50-burst application in Track 5 differentiates very small pores, micropores, and potentially oil-bearing matrix. Compared with the detail provided by the TLD and 50-burst logs, the standard-resolution analysis in Track 6 does not show any bedding but merely an average of the matrix.
Eagle Ford Shale, United States, North America, Onshore

Challenge: Discriminate intervals with the best production potential in what appears to be uniform matrix on standard log suites.

Solution: Run the newly developed 50-burst magnetic resonance acquisition application in combination with the Three-Detector Lithology Density (TLD) tool to discern both extremely low-porosity and mediumporosity laminations though statistical analysis.

Results: Used the improved ability to locate oilbearing laminated intervals to optimize placement of four additional laterals.

Products Used