Dynamic rock fragmentation: oil shale applications

Explosive rock fragmentation techniques used in many resource recovery operations have in the past relied heavily upon traditions of field experience for their design. As these resources, notably energy resources, become less accessible, it becomes increasingly important that fragmentation techniques be optimized and that methods be developed to effectively evaluate new or modified explosive deployment schemes. Computational procedures have significant potential in these areas, but practical applications must be preceded by a thorough understanding of the rock fracture phenomenon and the development of physically sound computational models. This paper presents some of the important features of a rock fragmentation model that was developed as part of a program directed at the preparation of subterranean beds for in situ processing of oil shale. The model, which has been implemented in a two-dimensional Lagrangian wavecode, employs a continuum damage concept to quantify the degree of fracturing and takes into account experimental observations that fracture strength and fragment dimensions depend on tensile strain rates. The basic premises of the model are considered in the paper as well as some comparisons between calculated results and observations from blasting experiments

True in-situ bed preparation: oil shale and tar sand

In 1978, a detailed study was conducted to evaluate the status of the bed preparation technology that had been developed for true in-situ processing of oil shale. It was concluded that the two techniques which had received the bulk of the attention in prior field experimentation, namely the wellbore springing and hydraulic/explosive fracturing concepts, both had inherent traits which would prevent them from being useful in practical applications. In the current paper, the previous results are reviewed to determine whether or not they are also applicable to tar sand. The conclusion reached is that neither technique would be practical for preparing a tar sands deposit for in-situ processing

Stress wave propagationin the site 12 hydraulic/explosive fracturing experiment

The Site 12 experiment was a heavily instrumented field event performed to examine the hydraulic/explosive fracturing concept for preparing an underground oil shale bed for true in situ processing. One of the key phases of this fracturing concept is the blasting operation which involves the insertion and detonation of slurry explosive in a pre-formed system of hydrofractures. To obtain a sound understanding of the nature of the blasting operations, a rather extensive array of stress gages, accelerometers, and time-of-arrival gages was installed in the rock mass in the vacinity of the explosive to monitor the dynamic events initiated by the detonation. These gages provided considerable amounts of information which were useful in evaluating overall results of the experiment. Details of the gage array, of the data, of analysis methods, and of the results and conclusions are considered in the report