Full-Wave Location Method

Our company provides a full cycle of microseismic emission monitoring surveys. This technology can be used to solve both the geological and technological challenges such as hydraulic fracture monitoring.

Application:

  • Hydraulic fracture monitoring (HFM)- to assess dynamics, dominant direction of fractures and estimate zones of proppant penetration. Field surveys are conducted from daylight surface, without lowering the equipment into neighboring wells
  • Natural fractures network mapping- to identify zones of active fracturing and determine the orientation of faults/fractures
  • Identification of anomalous objects in geological media- to improve the efficiency and safety of technological operations during the drilling, workover, well abandonment and monitoring of abandoned wells
  • Monitoring of fluid injection into reservoir- to determine fluid migration paths

Main stages of FWL method:


Hydraulic fracture monitoring is performed using our own technique of microseismic sources location based on maximum likelihood method. This method is theoretically the most accurate and noise immune among all known approaches.

Physical theory


Location of microseismic emission technique is well known in the world. It is based on phased array antenna technology which was originally used in radars for military purposes. There are several ways to realize this technique and the most common way is a diffraction stack method. Our company implements much more informative method for seismic events location based on maximum likelihood method.

Full-Wave Location method (FWL) is based on estimation of seismic tensor components, which maximize likelihood function. For this is necessary to know useful signal (simulated responses from deep source). Useful signal is a full-wave process registered on three components on observation points located at the surface. The responses are calculated by 3D numerical simulation of wave processes in viscoelastic media. Numerical model is created using information from structural maps and VSP data.

Source of the wave process is the force applied to nodes around the point of visualization in directions determined by components of the seismic moment tensor. This approach allows the best way to locate, identify the type of event and its characteristics in case of low signal / noise ratio at the receiving channels.

Numerical simulation

Solving the problem of microseismic emission location requires a very accurate model of geological medium. 2D seismic velocity model is not enough precise for this purpose. We obtain the geological model with the required accuracy using a structural seismic model and vertical seismic profiling (VSP) data or sonic logs.

Typically, the seismic events can’t be identified on the raw data. Our company use the technology to detect seismic impulses which are several times lower than the level of surface noises.

We get the waveform of impulse which comes to the sensor from a certain point in geological medium using numerical simulation. There is no any approximations in the numerical simulation, so we determine all the existing waves (P, S, R and others).

Processing and interpretation


The main problem of microseismic monitoring is a high coherent noise from surface sources. A significant part of the high-amplitude coherent component is eliminated at the stage of data pre-processing by the optimization method of quasi-harmonic noise filtering. Applying the method of maximum likelihood, the signals from the sensors with a high level of surface noise automatically get a low weight in the assessment of the most likely amplitude of seismic emission sources.

Processing and interpretation of FWL data include the following:

  • static and relief corrections
  • identification of microseismic activity zones based on microseismic emission sources location

Results of FWL survey are maps showing the development of microseismic activity zones.

Advantages

Advantages of Full-wave Location technology:

  • Field surveys are conducted from daylight surface using highly sensitive broadband seismometers. Wells shut-in, plug setting and downhole sensors run in nearby wells isn’t required
  • 3-component event location using full form of wave process, containing all wave types
  • Location technology automatically exclude influence of correlated noise
  • Retrieving of seismic moment tensor and location of seismic events. Implementation of maximum likelihood method allows locating seismic events even when the signal / noise ratio at the receiving channels equal to 1/100