Monitoring Dynamic Changes in Reservoir Production Using Time-Lapse Walkaway Das-Vsp Data

Abstract

With the rapid development of optical fibre sensing in recent years, Distributed Acoustic Sensing (DAS) is gradually considered as a viable alternative to borehole geophone arrays for the acquisition of borehole seismic or Vertical Seismic Profile (VSP) data. The data collected by an optical cable permanently deployed behind casing have a high degree of consistency and high SRN, which is less affected by receiving factors such as the cable coupling issues and the tube wave. This paper describes the time-lapse Walkaway DAS-VSP data acquisition in Dagang Oilfield of China and the multi-stage time-lapse Walkaway DAS-VSP data consistency processing procedures. Through the fine imaging processing of multi-stage Walkaway DAS-VSP data and detailed geological interpretation, it is possible to identify and map the range of fluid migration around the wellbore due to production, perform cross-validation during the monitoring period using the borehole oil production statistics information, and analyse the dynamic changes of reservoir fluids within the monitoring field. The Walkaway DAS-VSP survey has become an important development of the borehole seismic technique due to its advantages of high density, high efficiency, low cost and good consistency, which can be carried out with repeated observations and also for permanent monitoring. Therefore, the use of time-lapse Walkaway DAS-VSP surveys is proposed for the monitoring of oil and gas production in mature fields. The repeated time-lapse Walkaway DAS-VSP surveys can provide high-quality borehole seismic data for the study of dynamic changes of the reservoir fluid around the wellbore to a certain range. The key points of this paper mainly include: (1) Time-lapse Walkaway DAS-VSP data acquisition; (2) Special time-lapse Walkaway DAS-VSP data processing procedures; (3) Time-lapse Walkaway DAS-VSP data inversion; (4) Map reservoir fluid dynamic changes during the oil and gas production. In the application process of the time-lapse Walkaway DAS-VSP, the high-accuracy velocity fields, high-resolution structure imaging and multiple attribute inversion of the reservoir formation around the wellbore have been obtained. In addition, it also provides reservoir fluid identification and mapping based on high-accuracy Walkaway DAS-VSP and surface seismic data, which provide a basis for the establishment of multi-domain and multi-dimensional geological and reservoir models.