Hydraulic-fracturing-induced strain and microseismic using in situ distributed fiber-optic sensing

Abstract

Hydraulic fracturing operations in unconventional reservoirs are monitored using distributed fiber-optic sensing through which physical effects such as temperature, strain, and microseismic activity can be measured. When combined with treatment curves and other reservoir information, these measurements give engineers more data to understand the effectiveness of a treatment program and make future reservoir management decisions. Distributed fiber-optic data are acquired within a borehole that is actively being fractured and is subsequently used as an observation well for treatments of a neighboring well. The large-aperture and finely sampled data acquisition provides a variety of measurements at different resolution scales as changes are induced in the reservoir. Distributed acoustic sensing microseismic events are observed with magnitudes above −2. The spatial distribution of events, up to 500 m from the observation well, allows us to estimate diffusivity and fracturing trends for nearby treatment wells. Microseismic events acquired using a standard three-component borehole tool provide insight into the type of events that can be observed only on one system or simultaneously on both systems. We correlate very low frequency (well below 1 Hz) strain-front behavior with the onset of microseismic events, as they are triggered by pore pressure and fracturing progress throughout the reservoir.

Wireline distributed acoustic sensing allows 4.2 km deep vertical seismic profiling of the Rotliegend 150 °C geothermal reservoir in the North German Basin

“…In order to gain more detailed information on the structural setting and geometry of the reservoir, a 3-D seismic survey within an 8 km × 8 km permit area has been carried out in February and March 2017 (Krawczyk et al, 2019). In addition, VSP has been performed within the GrSk3 and GrSk4 wells.…”

Seismic Applications of Downhole DAS

“…Notwithstanding, as illustrated Figure 9 , microseismic events visible on DAS displayed interesting waveform characteristics, including mode conversions and reflections/scattering. Despite limitations in early detection capabilities, event location was attempted [ 102 , 104 ]. While the benefits of DAS-based location, mostly in positioning the event along the fiber axis, unfolded, the symmetry problem arising from recording on a single fiber limited the ability to retrieve unambiguous locations.…”

“…The ability to deploy DAS fibers in wells located inside unconventional hydrocarbon reservoirs offers unprecedented opportunities in reservoir monitoring [ 101 , 104 , 113 ]. DAS is a broadband instrument whose response function reaches frequencies lower than 0.001 Hz [ 48 ].…”

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].…”