A True In-Situ Fracturing Experiment Final Results

Abstract

Summary 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. Introduction 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).

Evaluation of Oil-Industry Stimulation Practices for Engineered Geothermal Systems

“…In the Tipton Shale, 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 Parrish et al, 1981. Results demonstrate that fractures were induced.…”

Carbon dioxide injection and associated hydraulic fracturing of reservoir formations

“…Theoretical and experimental investigations have been foremost in existing studies (Athavale and Miskimins, 2008, Blair et al, 1989, Casas et al, 2006, Daneshy, 1976, Daneshy, 1978, Elwood and Moore, 2009, Hanson et al, 1982, Hanson et al, 1981, Ishida, 2001, Ishida et al, 2004, Matsunaga et al, 1993, McLennan et al, 1986, Medlin and Masse, 1984, Murdoch, 1993a, Murdoch, 1993b, Murdoch, 1993c, Parrish et al, 1981, Teufel and Clark, 1984, Warpinski et al, 1982. For instance, Daneshy (1976) was able to draw an inference between some rock properties and the amount of pressure required for fracture extension, thereby establishing the term 'fracturability index'; Daneshy (1978) determined the effect of the strength of the interface between layered rock formations, as well as their relative mechanical properties on the pattern of fracturing; Murdoch (1993aMurdoch ( , 1993bMurdoch ( , 1993c carried out laboratory experiments and theoretical analysis to monitor pressure development and fracture propagation in soils; and more recently Athavale (2008) compared patterns of hydraulic fracturing between laminated (layered) and homogeneous materials.…”