4D seismic monitoring of the near wellbore space based on diffracted waves

LLC Sakhalin Energy, the operator of the Sakhalin-2 project, is developing the Piltun-Astokhskoye and Lunskoye oil and gas condensate fields. Ensuring the safe operation of hazardous production facilities remains an absolute priority at all stages of field development. A special place is occupied by the study of the processes and state of injection zones during the operation of injection and absorbing wells. This article is devoted to one of the elements of a comprehensive monitoring program, namely, 4D seismic monitoring of the near-wellbore space based on diffracted waves.

The fracture zone is a source of diffraction, so this technology is an important source of information about the depth, geometry and current state of the absorbing horizon.

Target. The main purpose of the work is to monitor the integrity of fluid seals, assess the risks associated with the operation of absorption and injection wells, as well as prevent complications when drilling adjacent wells. For this purpose, a method for 4D seismic monitoring of the near-wellbore space based on diffracted waves has been developed and implemented.

Materials and methods. Fractured formation zones generate diffracted waves that can be used to localize and geometrize the subsurface space, in particular, the areas of fracture development that form after fluid is injected into the well. The proposed method is based on the analysis of the 4D diffraction component of the wave field (the difference in the diffraction component between the base and monitor surveys). The calculation of the difference allows eliminating geological heterogeneities that have remained unchanged over time and highlighting the changes resulting from the exploitation of the field. This allows diffracted waves to be used directly, greatly improving the resolution of 4D data.

Results. The method for localizing the 4D diffraction component of the wave field was successfully implemented on the data of the Piltun-Astokhskoye oil and gas condensate field, which is being developed by Sakhalin Energy LLC.

Conclusion. The results obtained showed the high efficiency of this technology for the localization of fractured zones caused by injection into absorbing wells, as well as the confirmation by well logging data.

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