Summary
Shale oil reserves are of rich resources and great potential for exploration. Predicting shale brittleness comprehensively and accurately is of great significance to exploration and development of shale oil. Continental shale is characterized in that lateral lithofacies change fast, brittle mineral component changes considerably and much difference exists in buried depth. Past evaluation methods for brittleness based on elastic mechanical parameters or brittle mineral component, cannot accurately describe continental shale brittleness. This study proposes a prediction method of continental shale brittleness. Based on determination of the brittle-ductile transition depth in shale, combined with various pre stack and post stack seismic prediction technologies, it discusses the way to make seismic prediction of shale brittleness with different types of lithofacies and brittle mineral component. This method gets a preferable result in the prediction of shale brittleness in lower part of member 3 of Shahejie Formation (Es3) of LJ area in JY depression, eastern China, and it can provide some references for future exploration and development of continental shale oil.
Introduction
In recent years, encouraged by successful experience in the North American, Chinese shale oil exploration is becoming a priority project. At present, shale oil has been found in Bohai Bay Basin, Chaidamu Basin and Biyang sag and other regions of China, and has become an important field of oil and gas exploration in high mature exploration area. In the exploration and development of shale oil, formation brittleness is the main index for evaluating shale oil, and is also the important reference to fracturing layer selection. Predicting shale brittleness comprehensively and accurately is of great significance to exploration and development of shale oil.
Continental shale is characterized by fast lateral lithofacies change, considerable brittle mineral component change and much difference in buried depth. There are two evaluation methods for brittleness at present, one is based on elastic parameters (Poisson's ratio, Young's modulus) without considering the effect of different types of lithofacies. Another is based on brittle mineral component (the content of carbonate, quartz feldspar content) without considering the effect of different types of lithofacies and changes of buried depth. These two methods cannot comprehensively and accurately describe continental shale brittleness. At present, rock mechanics experiment in shale core sample can determine the brittle-ductile transition parameters, which can be used to evaluate shale brittleness. But this method is limited to the calculation of core samples, which cannot be popularized.
