Borehole Seismic: Essential Contributions Over the Oilfield Lifecycle

2021 ◽  
Author(s):  
Rajeev Kumar ◽  
Pierre Bettinelli

Abstract During the evolution of the petroleum industry, surface seismic imaging has played a critical role in reservoir characterization. In the early days, borehole seismic (BHS) was developed to complement surface seismic. However, in the last few decades, a wide range of BHS surveys has been introduced to cater to new and unique objectives over the oilfield lifecycle. In the exploration phase, vertical seismic profiling (VSP) provides critical time-depth information to bridge time indexed subsurface images to log/reservoir properties in depth. This information can be obtained using several methods like conventional wireline checkshot or zero-offset vertical seismic profiling (ZVSP), seismic while drilling (SWD) or distributed acoustic sensing (DAS) techniques. SWD is a relatively new technique to record real-time data using tool deployed in the bottomhole assembly without disturbing the drilling. It helps to improve decision making for safer drilling especially in new areas in a cost-effective manner. Recently, a breakthrough technology, distributed acoustic sensing (DAS), has been introduced, where data are recorded using a fiber-optic cable with lots of saving. ZVSP also provides several parameters like, attenuation coefficient (Q), multiples prediction, impedance, reflectivity etc., which helps with characterizing the subsurface and seismic reprocessing. In the appraisal phase, BHS applications vary from velocity model update, anisotropy estimation, well- tie to imaging VSPs. The three-component VSP data is best suited for imaging and amplitude variation with offset (AVO) due to several factors like less noise interference due to quiet downhole environment, higher frequency bandwidth, proximity to the reflector, etc. Different type of VSP surveys (offset, walkaway, walkaround etc.) were designed to fulfill objectives like imaging, AVO, Q, anisotropy, and fracture mapping. In the development phase, high-resolution images (3D VSP, walkaway, or crosswell) from BHS surveys can assist with optimizing the drilling of new wells and, hence reduce costs. it can help with landing point selection, horizontal section placement, and refining interpretation for reserve calculation. BHS offers a wide range of surveys to assist the oilfield lifecycle during the production phase. Microseismic monitoring is an industry-known service to optimize hydraulic fracturing and is the only technique that captures the induced seismicity generated by hydraulic fracturing and estimate the fracture geometry (height, width, and azimuth) and in real time. During enhanced oil recovery (EOR) projects, BHS can be useful to optimize the hydrocarbon drainage strategies by mapping the fluid movement (CO2, water, steam) using time-lapse surveys like walkaway, 3D VSP and/or crosswell. DAS has brought a new dimension to provide vital information on injection or production evaluation, leak detection, flow behind tubing, crossflow diagnosis, and cement evaluation during production phase. This paper highlights the usage of BHS over the lifecycle of the oilfield.

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. T225-T235
Author(s):  
Gary Binder ◽  
Aleksei Titov ◽  
Youfang Liu ◽  
James Simmons ◽  
Ali Tura ◽  
...  

In 2017, distributed acoustic sensing (DAS) technology was deployed in a horizontal well to conduct a vertical seismic profiling survey before and after each of 78 hydraulic fracturing stages. From two vibroseis source locations at the surface, time shifts of P- and S-waves were observed but decayed over days. Some stages also showed waves scattered off the stimulated rock volume. We have used 2D finite difference elastic wavefield modeling to understand these observations and connect them to underlying properties of the stimulated rock. We have developed an effective medium model of vertical fractures that close exponentially with time as fluid leaks off into the formation can match the distribution of P- and S-wave time shifts along the well. This has enabled estimates of the height, normal and tangential fracture compliance values, and decay time of the stimulated rock volume. Additionally, the kinematics of scattered waves observed in the data have been found to be consistent with PS conversion across the stimulated rock volume from an individual stage. With higher quality DAS data, stage-by-stage inversion for height, fracture compliance, and decay time attributes may be possible for characterizing variations in the effectiveness of hydraulic fracturing.


Author(s):  
Sudhish K. Bakku* ◽  
Michael Fehler ◽  
Peter Wills ◽  
Jeff Mestayer ◽  
Albena Mateeva ◽  
...  

Solid Earth ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 521-537
Author(s):  
Jan Henninges ◽  
Evgeniia Martuganova ◽  
Manfred Stiller ◽  
Ben Norden ◽  
Charlotte M. Krawczyk

Abstract. We performed so-far-unprecedented deep wireline vertical seismic profiling at the Groß Schönebeck site with the novel method of distributed acoustic sensing (DAS) to gain more detailed information on the structural setting and geometry of the geothermal reservoir, which is comprised of volcanic rocks and sediments of Lower Permian age. During the survey of 4 d only, we acquired data for 61 source positions using hybrid wireline fiber-optic sensor cables deployed in two 4.3 km deep, already existing wells. While most of the recorded data have a very good signal-to-noise ratio, individual sections of the profiles are affected by characteristic coherent noise patterns. This ringing noise results from incomplete coupling of the sensor cable to the borehole wall, and it can be suppressed to a large extent using suitable filtering methods. After conversion to strain rate, the DAS data exhibit a high similarity to the vertical component data of a conventional borehole geophone. We derived accurate time–depth relationships, interval velocities, and corridor stacks from the recorded data. Based on integration with other well data and geological information, we show that the top of a porous and permeable sandstone interval of the geothermal reservoir can be identified by a positive reflection event. Overall, the sequence of reflection events shows a different character for both wells explained by lateral changes in lithology. The top of the volcanic rocks has a somewhat different seismic response in both wells, and no clear reflection event is obvious at the postulated base of the volcanic rocks, so that their thickness cannot be inferred from individual reflection events in the seismic data alone. The DAS method enabled measurements at elevated temperatures up to 150 ∘C over extended periods and led to significant time and cost savings compared to deployment of a conventional borehole geophone string. This wireline approach finally suggests significant implications for observation options in old wells for a variety of purposes.


2019 ◽  
Author(s):  
Andreas Ellmauthaler ◽  
William Palacios ◽  
Michel LeBlanc ◽  
Mark Willis ◽  
George Knapo

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