Time-frequency electromagnetic fracturing monitoring system and method based on distributed optical fiber sensing

Abstract

The invention provides a time-frequency electromagnetic fracturing monitoring system and method based on distributed optical fiber sensing. The method comprises the steps: employing a three-dimensional three-component optical fiber time-frequency electromagnetic data acquisition station arranged on the ground above a fracturing well section in a horizontal well, an underground time-frequency electromagnetic data acquisition armored optical cable or cable which is arranged in an observation well near a fracturing well or outside a fracturing well sleeve, and high-power dipole current sources which are arranged on the two sides of a fracturing horizontal well section and are parallel to the fracturing well section, and continuously and synchronously collecting three-dimensional three-component time-frequency electromagnetic data of the ground or a ground-well before fracturing, in the fracturing process and after fracturing is finished. Calculating the difference between the three-dimensional three-component time-frequency electromagnetic data acquired in the fracturing process and after fracturing and the three-dimensional three-component time-frequency electromagnetic data acquiredbefore fracturing is started in real time, and inverting the distribution of underground resistivity in different fracturing stages according to the actually measured three-dimensional three-component time-frequency electromagnetic data of the ground or the ground well; and evaluating the fracturing effect in real time by using the distribution of the underground resistivity in different fracturing stages.

Description

technical field [0001] The invention belongs to the technical field of geophysical exploration, in particular to a time-frequency electromagnetic fracturing monitoring system and monitoring method based on distributed optical fiber sensing. Background technique [0002] The induction electromagnetic prospecting method, referred to as the electromagnetic method, refers to a method that uses the electromagnetic difference of the medium as the material basis, and achieves certain exploration purposes by observing and studying the artificial or natural alternating electromagnetic field with the spatial distribution or time-varying law. Electrical prospecting method. [0003] The prospecting principle of electromagnetic prospecting is based on the change of electrical properties between different rocks and ores, which causes corresponding changes in the spatial distribution of electromagnetic fields (artificial and natural). Therefore, people can use instruments with different p...

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Problems solved by technology

[0009] Currently widely used controllable source time-frequency electromagnetic or transient electromagnetic prospecting methods and long offset transient electromagnetic prospecting methods only deploy one excitation field source, and can only receive electromagnetic field signals within a certain range near the field source. When the excitation energy of the long-distance receiving point cannot meet the requirements of the signal-to-noise ratio of the received signal, choose a suitable location to re-arrange the field source

There are a series of problems in the signal of a single excitation field source: first, due to the complexity of the underground structure, the excitation field at different positions or orientations will have obvious differences at the receiving point due to the difference in the transmission process of the electromagnetic field; second, the distance from the field source is different, through The field source signal components and energies arriving at the receiving point on the ground, in the air and underground are very different, therefore, the field source characteristics at the receiving point are different

When the horizontal well is deep (more than 2500 meters), the ground or shallow well microseismic monitoring technology can only receive microseismic events with large magnitude or energy because the geophone of the ground or shallow well is too far away from the fractured well section. The number of microseismic events that can be monitored is much less than the downhole microseismic monitoring of adjacent wells for fracturing wells, and it cannot monitor the actual extension of rock fractures caused by hydraulic fracturing well in real time.

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