Acoustic Log Measurements in the Lower Eagle Ford Formation in Brazos and Robertson Counties, Texas and Their Implications on Completion Design

Abstract

Intrinsic anisotropy is known to exist in most organic shales due to their layered nature. Horizontal and vertical mechanical properties can sometimes be drastically different. Taking these differences into account can result in higher than expected pre-job calculated frac gradients. Often this type of information is based solely on experience gained from hydraulically fracturing other wells in a given area. Logging data obtained prior to stimulation can help predict these higher fracture gradients and can provide great value in the design of an optimized stimulation. This study documents the integration of log data obtained in a vertical pilot well and its associated lateral wellbore in the lower Eagle Ford formation in Robertson county, Texas. Acoustic data obtained from a dipole sonic that was run in the vertical pilot were correlated with data acquired from a new slim dipole array sonic tool that was conveyed through the drillstring in a lateral well and into open hole after it was drilled. Slowness measurements taken from the vertical and horizontal well data sets suggest that a high amount of intrinsic anisotropy was present. These predictions were confirmed by the post job stimulation data from the horizontal well. Combining the stress and petrophysical interpretations based on other log measurements provided reservoir and stimulation quality indicators that were then compared to actual production. Lessons learned were then implemented in later wells resulting in improved stimulation efficiency and production.