Characteristics of high-temperature steam fracturing and seepage-heat transfer of meter-scale oil shale under the constraint of geostress
In order to investigate the process and mechanism of in-situ fracturing of oil shale with high-temperature steam,and to evaluate the temporal and spatial evolution of temperature and pres-sure during pyrolysis of the formation by high-temperature steam along the fractured cracks.The large size(meter scale)oil shale was used as the research object.The macroscopic fracturing-percolation-heat transfer characteristics of oil shale reservoirs under the constraint of geostress and under the continuous action of high-temperature steam were investigated by laboratory physical simula-tion.The results of the test show that:High-temperature steam fracturing needs to overcome the constraint of the superposition of formation stress and thermal stress.The fracturing pres-sure is high,which can be up to twice the in-situ stress.The roof and floor of oil shale are dense and low-permeability,which can play a good role in heat preservation and heat insulation of the fracturing orebody.The pyrolysis area is controlled by the flow law of steam completely.During pyrolysis of the formation by high-temperature steam along the fractured cracks,the steam pressure(maximum 0.97 MPa)is much lower than the formation stress(3.82 MPa),and the pressures in the two wells show synergistic and consistent changes when the heat injec-tion wells and the production wells are connected.In the process of in-situ mining of low-geostress oil shale by heat injection,high-temperature steam fracturing technology can be used.After fracturing,the seepage channel of the orebody is good,and the injection of low-pressure steam into the orebody can realize extensive pyrolysis,and the direction of the pyroly-sis area can be quickly controlled through the rotation and regulation of heat-injection wells and production wells.
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