Estimation of total organic carbon and brittleness volume

Abstract

The Barnett Shale in the Fort Worth Basin is one of the most important resource plays in the USA. The total organic carbon (TOC) and brittleness can help to characterize a resource play to assist in the search for sweet spots. Higher TOC or organic content are generally associated with hydrocarbon storage and with rocks that are ductile in nature. However, brittle rocks are more amenable to fracturing with the fractures faces more resistant to proppant embedment. Productive intervals within a resource play should therefore contain a judicious mix of organics and mineralogy that lends to hydraulic fracturing. Identification of these intervals through core acquisition and laboratory-based petrophysical measurements can be accurate but expensive in comparison with wireline logging. We have estimated TOC from wireline logs using Passey’s method and attained a correlation of 60%. However, errors in the baseline interpretation can lead to inaccurate TOC. Using nonlinear regression with Passey’s TOC, normalized stratigraphic height, and acquired wireline logs, the correlation increased to 80%. This regression can be applied to uncored wells with logs to estimate TOC, and we used it as a ground truth in integrated analysis of seismic and well log data. The brittleness index (BI) is computed based on core Fourier transform infrared mineralogy using Wang and Gale’s formula. The correlation between core BI and estimated BI using elastic logs ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]) combined with wireline logs was 78%. However, this correlation decreases to 66% if the BI is estimated using only wireline logs. Therefore, the later serves as a less reliable proxy. We have correlated production to volumetric estimate of TOC and brittleness by computing distance-weighted averages in 120 horizontal wells. We have obtained a production correlation of 38% on blind wells, which was encouraging, suggesting that the geologic component in completions provides an important contribution to well success.