Mechanical Stratigraphy and Well Correlation Using the Proceq Bambino in the Niobrara Shale

Abstract

The Proceq Bambino is a hand-held rebound hammer that can measure brittleness through non-destructive testing and increase the resolution, accuracy, and confidence in lateral geomechanical estimations. Ernst Schmidt invented the Schmidt Rebound Hammer in 1948. The Schmidt Hammer consisted of a spring-loaded hammer. When the hammer was released and impacted a surface, the height of the hammer rebound would be recorded. The Schmidt Hammer was produced by Proceq and originally used in concrete quality assurance testing. It was preferable to other testing methods because it could be conducted in-situ and was non-destructive. Schmidt Hammer rebound values could be correlated to unconfined compressive strength (UCS). The Schmidt Hammer was not ideal for core testing due to high impact velocity and destruction of core samples. In 2006, Proceq developed a hand-held, low impact velocity rebound hammer, the Bambino. The Bambino had an LCD display and an internal memory storage device mounted onto the shaft. While the Schmidt Hammer only recorded rebound height, the Bambino gave readings in Leeb Hardness (HLD). An HLD unit was calculated as the ratio of rebound velocity to impact velocity (VREB/VIMP). Preliminary data was taken from a Niobrara core to demonstrate the repeatability, precision, and non-destructiveness of the Bambino. A relationship between HLD values and geomechanical properties such as UCS, Young's Modulus, and Poisson's ratio was found after conducting Bambino testing on cores from the Niobrara Shale. These relationships, coupled with the non-destructive, high-resolution data collection methods of the Bambino, made the Bambino a useful tool in geomechanical characterization of the Niobrara. The Niobrara is a late Cretaceous formation located in the Denver Basin. The Niobrara is composed of two members, The Fort Hays Limestone and the overlying Smoky Hill Chalk. A series of chalk-marl sequences make up the Smoky Hill member. Each chalk-marl sequence showed a characteristic HLD value range. The differences in HLD values from differing lithologies and sequences was attributed to the Bambino's sensitivity to lithologic and microstructure changes. The HLD values were used to determine brittleness. Brittleness characterization greatly impacts the ability to predict hydraulic fracturability and fracture propagation. Currently, these geomechanical properties can only be determined for cored intervals. The high cost and scarcity of cored intervals, therefore, limits the amount of geomechanical data available in a given basin. A correlation between geomechanical logs and sonic logs was made. As this correlation is better understood and refined, geomechanical properties can be predicted for wells where no core is available. Accurate predictions can greatly improve the efficiency of fracture stimulation designs, forecasts, and simulations.

AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014