Time-lapse seismic monitoring of individual hydraulic frac stages using a downhole DAS array

Abstract

A fiber-optic distributed acoustic sensing system (DAS) was recently installed in an Apache-operated horizontal shale well and used to acquire downhole seismic data before, during, and after the well was treated in order to better understand the time-lapse seismic response to hydraulically stimulated fractures. In addition to a 3D/4D DAS vertical seismic profiling survey acquired before and after the well was treated, data were recorded from two fixed shot locations approximately 1 mile off each end of the lateral part of the well. These shots were repeated after each of the 78 frac stages used to treat the well in an attempt to achieve more continuous seismic monitoring of the hydraulic-stimulation process. Despite the noisy environment associated with ongoing frac operations, these data proved to be valuable in understanding the fundamental seismic response to each frac stage. The dominant time-lapse effect observed in the stage-by-stage data was a subtle time delay of the P-wave direct arrival when compared to data recorded prior to stimulation. This time-lapse effect was only present over a period of a few days once the stage was completed and would have been completely missed using the conventional approach of having a single monitor survey acquired after the well was treated. It was possible to model the kinematics of the P- and S-wave arrivals and invert for frac effectiveness at each stage based on the observed time delay in the seismic. Amplitude differences were also observed in the time-lapse shot records in which new waveforms appeared along the hydraulically stimulated portions of the well.

Advancement of Hydraulic Fracture Diagnostics in Unconventional Formations

“…DAS applications such as ball tracking, injection/production profiling, cluster efficiency evaluation, and interstage communication rely on signal intensity in high-frequency bands [44,48,49]. DAS may also be used to conduct time-lapse vertical seismic profiles [50][51][52], to monitor microseismic events [53][54][55], and to measure cross-well strain variations [56]. One of the most important applications of DAS technology is the diagnosis of multistage fracture treatment in horizontal wells [57].…”

“…One of the most important applications of DAS technology is the diagnosis of multistage fracture treatment in horizontal wells [57]. DAS can also be used to conduct time-lapse vertical seismic (VSP) profiles [50][51][52] and to monitor microseismic events [53][54][55]. These findings have been used to quantify and estimate the geometry of far-field hydraulic fractures.…”

Recent Progress in Distributed Fiber Acoustic Sensing with Φ-OTDR

“…The results of DAS are evaluated with those of conventional geophone array, and the feasibility is verified in field test. After that, Lawrence Berkely National Laboratory [ 9 ] and Apache Corporation [ 10 ] report their works on VSP and time-lapse VSP for resource exploration. In China, some groups are also working on this, such as, Puniu Tech., Optical science and technology (Chengdu) Ltd., etc.…”

“…Up to now, DAS has been deeply studied, and state-of-the-art DAS systems are capable of monitoring physical fields with spatial resolution accurate to sub meter scale and sampling rates up to kHz over a distance of tens of kilometers. With the joint efforts, DAS has been widely applied in many important fields, for instance, perimeter security [ 1 ], railway transportation [ 2 , 3 , 4 ], pipeline safety monitoring [ 5 , 6 , 7 ], nature hazard detection [ 8 ], geophysical prospecting [ 9 , 10 ], etc. It is noteworthy, recent researches make DAS hopeful to light all dark communication fibers in the global [ 11 , 12 ] for unprecedented large-scale pervasive sensing.…”

Investigation of the Time-Lapse Changes with the DAS Borehole Data at the Brady Geothermal Field Using Deconvolution Interferometry

“…The DAS has been used in boreholes environments for a variety of applications. These include flow monitoring [2][3][4], wellbore diagnostics [2,4,5], vertical seismic profiling [VSP; [6][7][8][9], hydraulic fracture characterization [10,11], and microseismicity detection [12]. The DAS is suitable for borehole monitoring for several reasons [13,14]: First, the DAS fiber has higher endurance in high temperature, high pressure, and corrosive environments compared to geophones.…”