EAGE GeoTech 2022 Third EAGE Workshop on Distributed Fibre Optic Sensing

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 analysis the dynamic changes of reservoir fluids within the monitoring field. 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.

Near-surface imaging is crucial for a broad range of studies, with seismic monitoring becoming an increasingly important tool due to recent developments in Distributed Acoustic Sensing (DAS) and ambient noise interferometry (ANI). Using a dataset acquired on the Rutford Ice Stream, West Antarctic, we develop ANI approach for DAS datasets which retrieves the Rayleigh wave response from the ambient seismic wavefield. We find that a conventional ANI approach, which uses a single DAS channel as a virtual source and the entire continuous dataset is stacked, produces unstable, poor quality interferograms. This is due to coherent instrument noise and an absence of continuous ambient seismic noise. To overcome these issues, we develop an approach based on selective-stacking and hybrid seismic receivers, which significantly improves the quality of the Rayleigh waves retrieved using DAS. Our findings highlight the impacts that coherent DAS instrument noise and the transient nature of seismic noise above 1Hz has on ambient seismic noise studies.

Following a multi-year test and develop campaign bp have successfully deployed and acquired data on a subsea DAS VSP system. This is the first ever deployment of a DAS acquisition system on a subsea well. We describe the technical challenges, system design and optical parameters. The preparation and actual installation are explained, along with checks performs during the installation. The highest risk to the project was ensuring the data quality would meet the requirements for high resolution VSP interpretation. We specifically consider the impact of optical loss, coupling and interrogator settings on the data quality. Data is presented from both flowing and shut-in conditions, considering the impact of production noise on the VSP data quality. A comprehensive set of parameters were used to evaluate the DAS VSP performance. These quantitative methods are discussed, showing that the data quality exceeded expectation allowing good acquisition of reflected P-waves from the lookahead reservoir interval.

In a context of an acceleration Global Warming, the study of the effects of the climate change appears of major importance to monitor environmental properties variations and alert about possible dramatic associated risks. The work presented in this paper proposes a solution for long-term monitoring and analysis of this decline using an easy to deploy and high performances solution. We base our study on a seismic campaign led in a small-scale representation of the Arctic ice cap: a frozen lake located in the Alps. This survey had been recorded using Distributed Acoustic Sensing (DAS) interrogator enabling to turn a simple fiber optic cable into hundreds to thousands of acoustic sensors. We analyze the recorded signal associated with guided wave, and more precisely the associated dispersion curves, holding the information about mechanical properties of the ice. We then determine, from inversion methods, an ice thickness of h=47cm with a Young modulus equal to E=3.4±0.1GPa. These results are in accordance with ice properties observed in the field. The presented solution then appears as a relevant tool for the long-term analysis of the effects of climate change on ice layers such as ice cap, glaciers, or mountain lakes.