METHOD TO DETERMINE GEOMETRIC CHARACTERISTICS OF HYDRAULIC FRACTURING CRACK Russian patent published in 2015 - IPC G01V1/42 E21B47/14 

FIELD: oil and gas industry.

SUBSTANCE: method is proposed to determine geometric characteristics of a hydraulic fracturing crack: seismic sensors are placed on the day surface, microseismic signals are recorded, the recorded signals are processed. Seismic sensors are installed on the day surface in the area of a hydraulic fracturing well, in which the ratio "intensity of a seismic signal of hydraulic fracturing crack formation" / "intensity of seismic noise" is the maximum, distances between the sensors are chosen from a set of values L=λ(n+1/2), where L - distance between the sensors, λ - Rayleigh wave length of the working frequency, n - non-negative integer number, therefore, with the number of sensors used in monitoring of hydraulic fracturing they produce a ring around the well with an external radius of the order of the depth of carried out hydraulic fracturing, the working frequency is chosen from capabilities of measurement equipment, as well as suggested dominant frequency of pulses from the hydraulic fracturing crack. The value of energy of the seismic signal of the hydraulic fracturing crack formation in the surveillance station is calculated by numerical modelling of the propagation of seismic waves from a source in the centre of a potential area of propagation of hydraulic fracturing cracks. The value of energy of background noise is measured in the area of performance of works by the seismic sensors to the start of hydraulic fracturing works performance in a point most remote from sources of noise. The value of energy of noise from the hydraulic fracturing fleet and other surface sources of seismic noise is calculated on the basis of measurements of the noise energy dependence on the distance or on the basis of previous measurements of noise energy for the conditions similar to the investigated area. Microseismic data is recorded during hydraulic fracturing. Recovery of the spatial position, time and intensity of seismic events that accompany the formation of the hydraulic fracturing crack is carried out using the method of the maximum likelihood for the recovery of signal characteristics during multi-channel reception, for which purpose using the numerical modelling method they calculate the shape of the signal from microseismic events in points of suggested area of hydraulic fracturing, arranged according to a discrete mesh, with discrecity determined by the working frequency, in units of the numerical model, corresponding to the points of the sensors installation, counting each component of the sensor as a separate channel. Noise distribution probability density is restored for each channel by the approximation of the observed variational series. For each discrete moment of time of hydraulic fracturing performance for each point of the signal recovery they restore the most likely amplitude of seismic emission. Final filtration of time rows is carried out in the points of the signal recovery, as well as spatial interpolation of the accumulated energy of restored seismic emission with the production of final charts of the hydraulic fracturing crack propagation.

EFFECT: increased accuracy of determination of geometric characteristics of a hydraulic fracturing crack.

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