Inferring Hydraulic Connectivity of Induced Fractures in the Near-wellbore Region Using DAS-recorded Tube Waves Excited by Perforation Shots

We present a novel use of tube waves exited by perforation (or “perf”) shots and recorded on distributed acoustic sensing (DAS) to infer and compare the hydraulic connectivity of induced fractures near the wellbore on a stage-by-stage basis. Evaluating the fracture connectivity near the wellbore is critical since it controls the flow of the hydrocarbons from the formation to the wellbore. Currently, there are no established methods used to assess this property. However, we discuss how tube wave decay rates can be used to infer relative differences in fracture connectivity between stages and, through field observations on DAS, demonstrate the correlation between decay rates and frac effectiveness. Additionally, we consider other potential uses of this data in unconventional wells such as assessing plug integrity and constraining fracture geometry with Krauklis waves. DAS data is commonly acquired during the perf shots but primarily for fiber depth calibration purposes and has not been well studied. Our work illustrates the untapped potential of this data and how it can be easily repurposed to bring new insights about fracture characteristics in the near-wellbore region.

Using Sound and Vibration Signals to Understand the Subsurface

A new book explores Distributed Acoustic Sensing, a technology with a range of applications across geophysics and related fields.

Switchable acoustic metagrating for three-channel retroreflection and carpet cloaking

In this paper, we propose a switchable acoustic metagrating composed of periodic grooves for realizing switchable functionalities of three-channel retroreflection and carpet cloaking. The groove parameters are determined by calculating and analyzing the reflectance of different diffracted waves, and only one propagating reflected wave is allowed. Theoretical analysis and numerical simulations are performed to validate the three-channel retroreflection and carpet cloaking performances of the proposed metagrating. Our research work provides a practical and simple method to design acoustic devices with switchable functionalities and simple structure, and has potential applications in practical fields of acoustic sensing and acoustic communication.

Sensing Iceland’s Most Active Volcano with a “Buried Hair”

Distributed acoustic sensing offered researchers a means to measure ground deformation from atop ice-clad Gr�msv�tn volcano with unprecedented spatial and temporal resolutions.

Borehole Seismic: Essential Contributions Over the Oilfield Lifecycle

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.