地应力约束下米级油页岩高温蒸汽压裂与渗流-传热特征

Characteristics of high-temperature steam fracturing and seepage-heat transfer of meter-scale oil shale under the constraint of geostress

为了探明高温蒸汽原位压裂油页岩的过程与机理,评价高温蒸汽沿着压裂裂缝热解矿层过程中温压时空演变规律,以大尺寸(米级)油页岩作为研究对象,采用实验室物理模拟的方法研究了在地应力约束下油页岩储层在高温蒸汽持续作用下表现的宏观压裂-渗流-传热特性.试验结果显示:高温蒸汽压裂需要克服地层应力和热应力叠加的约束作用,起裂压力值高,可达地应力的2倍;油页岩顶底板致密低渗,可以对压裂矿层起到较好的保温和隔热作用,热解区域完全靠蒸汽的流动规律控制;高温蒸汽沿着压裂裂缝热解矿层过程中,蒸汽压力(最大0.97 MPa)要远低于地层应力(3.82 MPa),当蒸汽沟通注热井和生产井时,二者的压力表现出协同一致的变化特征.在低地应力油页岩原位注热开采过程中,可以采用高温蒸汽压裂技术,压裂后矿层渗流通道良好,在矿层中注入较低压力的蒸汽便可实现大范围热解,通过注热井和生产井的轮换和调控,可以快速控制热解区域的走向.

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 pressure 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-percolationheat 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 simulation.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 pressure 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 agood 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 0.97MPa)is much lower than the formation stress(3.82MPa),and the pressures in the two wells show synergistic and consistent changes when the heat injection wells and the production wells are connected.In the process of in-situ mining of lowgeostress 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 lowpressure steam into the orebody can realize extensive pyrolysis,and the direction of the pyrolysis area can be quickly controlled through the rotation and regulation of heat-injection wells and production wells.