Fracturing of oil shale

The steps in assembling the computational tools needed to simulate the explosive fracture of oil shale have been described. The resulting code, with its input data, was then used to simulate three explosive field experiments. The results of the calculations are in good agreement with what actually occurred in the field. Further detailed comparisons are in progress for these experiments and the others that have been conducted. As this is done, improvements will be made in the input data and in the code physics. 

Olinger, B. "Oil Shales under Dynamic Stress," in "Explosively Produced Fracture of Oil Shale, April 1977-March 1978," Los Alamos Scientific Laboratory report LA-7357-PR, November 1978, pp. 2-10. 

Fracturing of Oil Shale by Treatment with Liquid Sulfur Dioxide... 

Figure 1. Representative examples of the fracturing of oil shales by liquid S02 (left,) treated samples fright,) untreated samples (a) Antrim shale treated at 170°C for 2 h (b) Green River shale treated at 70°C for 2 h (c) Moroccan shale treated...

During the second step of the fracturing experiments at this site, 60% dynamite was detonated in the five wells to relieve stress conditions in the block of oil shale. Each of the wells in the 25- by 25-ft five-spot pattern was loaded with 45-lb charges of 60% dynamite on detonating cord with electric caps attached and detonated simultaneously (shot B). 

Six shots (C, D, G, H, I, K) using approximately 1000 lb of TNT, were detonated in well 5 at depths ranging from 67 to 88 ft. The first three shots were not stemmed consequently, water and debris were blown to the atmosphere. The last three shots were sand tamped to the surface to fragment the maximum amount of oil shale around the wellbore and to permit the contained explosive gases to extend the induced fractures. 

Results. Data obtained from evaluation tests indicated that the oil shale was fractured and/or fragmented from the explosive work. Three of these tests indicated either formation damage and/or increased fracturing of the shale existed between wells. 

Results of explosive fracturing tests in oil shale show that NG1 will detonate and that the explosion will propagate in water-filled natural fractures and sand-propped, hydraulically induced fractures in oil shale. The shale was fragmented by this method, and a successful underground retorting experiment to recover shale oil was performed. 

Here we wish to report the results of preliminary experiments in which oil shales are treated with liquid sulfur dioxide to effect fracturing observations made during these experiments suggest that liquid SO2 may also be of utility in other phases of oil shale processing. We are, presently, unaware of any previous reports of such experiments. 

Grady, D. E., Kipp, M. E. (1980). Continuum Modeling of Explosive Fracture in Oil-Shale. International Journal of Rock Mechanics and Mining Sciences, 17,147-157. doi 10.1016/0148-9062(80)91361-3... 

Every branch of science, every profession, and every engineering process has its own language for communication. Hydraulic fracturing and shale-oil mining are no different. To work even at the edge of oil-shale fracking, you must acquire a fundamental vocabulary for the processes involved. 

The data shown in Fig. 8.11 are for an 80 ml/kg grade oil shale obtained from a mine near central Colorado. Oil shale grades from this region vary from 40-320 ml/kg. Properties such as fracture toughness and elastic constants are found to depend on oil shale grade. For the oil shale studied in Fig. 8.11, a fracture toughness of x 0.9 MN/m, a density of p = 2000 kg/m and an elastic wave speed of c = 3000 m/s are representative. 

The theoretieal fraeture parameters in (8.22) and (8.23), based on a model assuming an inherent power law fracture flaw distribution and a constant fracture growth velocity, can be determined with the strain rate dependent fracture data in Fig. 8.11 (Grady and Kipp, 1980). Using the fracture data for oil shale provides a value of m = 8 and a fracture stress dependence on strain... 

Numerical simulation of a complex dynamic fracture application can be illustrated by calculations of impact induced damage in a ceramic cylinder. The computer model used was originally developed for oil shale explosive fragmentation (Grady and Kipp, 1980), with various extended applications considered by Boade et al. (1981) and Chen et al. (1983). In this model, stress and strain are related through... 

The parameters for the model were originally evaluated for oil shale, a material for which substantial fracture stress and fragment size data depending on strain rate were available (see Fig. 8.11). In the case of a less well-characterized brittle material, the parameters may be inferred from the shear-wave velocity and a dynamic fracture or spall stress at a known strain rate. In particular, is approximately one-third the shear-wave velocity, m has been shown to be about 6 for various brittle materials (Grady and Lipkin, 1980), and k can then be determined from a known dynamic fracture stress using an analytic solution of (8.65), (8.66) and (8.68) in one dimension for constant strain rate. 

It is possible that greater porosity in shale beds could be achieved by chemical comminution of the shale. For example, the treatment of western oil shales with acid solutions might result in comminution by inducing corrosive stress fracture of the carbonate rock. Chemical engineering research in this area, as well in the elucidation of oil-rock interactions, might provide insights for new strategies for oil shale production. 

As much as two-thirds of conventional crude oil discovered in U.S. fields remain unproduced, left behind because of the physics of fluid flow. In addition, hydrocarbons in unconventional rocks or that have unconventional characteristics (such as oil in fractured shales, kerogen in oil shale or bitumen in tar sands) constitute an enormous potential domestic supply of energy. 

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