A True In-Situ Fracturing Experiment Final Results
- R.L. Parrish (Sandia Natl. Laboratories) | A.L. Stevens (Sandia Natl. Laboratories) | T.F. Turner Jr. (U.S. DOE)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- July 1981
- Document Type
- Journal Paper
- 1,297 - 1,304
- 1981. Not subject to copyright. This document was prepared by government employees or with government funding that places it in the public domain.
- 5.6.5 Tracers, 5.6.1 Open hole/cased hole log analysis, 2.4.3 Sand/Solids Control, 3.3.1 Production Logging, 1.6.9 Coring, Fishing, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.1.5 Processing Equipment, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.1.7 Seismic Processing and Interpretation, 4.1.2 Separation and Treating
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A true in-situ oil shale retort bed preparation experiment was performed by detonating an explosive slurry that had been displaced from well bores into preformed horizontal hydraulic fractures. The objective was to test this method for producing a distributed fracture network with sufficient void and permeability for retorting in a controlled manner. Numerous diagnostic and evaluation measurements were performed during the course of the experiment for initial site characterization, hydraulic fracture assessment, explosive displacement and detonation performance, and post detonation fracture and permeability assessment. Results show that fractures were induced; the fractures were found to be randomly distributed with no regions of extensive fracturing or shale dislocation. Enhancement of permeability was limited essentially to enlargement of the preformed hydraulic fracture horizons into which the explosive slurry was inserted and detonated. Successful retorting would be contingent on the ability to retort shale layers with random fractures but without significant permeability between the enlarged fractures.
The potential advantages of true in-situ processing techniques, as compared with mining and surface retorting, for extracting hydrocarbons from oil shale have been recognized for many years. With such techniques, the only linkage between the underground shale bed and the surface is through a series of wells. Both the bed preparation and the retort processing phases are conducted from the surface through these wells. Resulting attractive features are that requirements for mining large quantities of raw shale and disposal of the spent shale are eliminated. Other environmental impacts, such as water requirements, may be reduced significantly.
In preparing an oil shale bed for in-situ processing, the naturally impermeable oil shale must be rubblized to introduce sufficient void and permeability. This permits process gases to flow from injection wells to the combustion front and permits product liquids and gases to flow from the pyrolysis zone to production wells during retorting. Past experiments1,2 have used variations of two basic methods (well bore springing and hydraulic/explosive fracturing) to fracture the shale bed and attempt to achieve the required void and permeability. The well bore springing method3 involves the detonation of explosive charges contained within the well, while the hydraulic/explosive fracturing method involves the detonation of slurry explosives that have been displaced from wells into preformed horizontal hydraulic fractures (hereafter called hydrofractures or simply cracks).
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