|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
Hydraulic fracturing of lateral shale wells generates complex fracture networks with predominantly vertical fracture sets. Evaluating stimulated reservoir volume (SRV) is critical to understanding well productivity. To this end, we have developed a quantitative interpretation to evaluate fracture height and density from time-lapse DAS VSP data. We model P-wave time delays due to induced vertical fracture sets as horizontal transverse isotropic (HTI) zones, and we use rock physics to relate seismic anisotropy to fracture properties. An inversion of P-wave time delays can then recover the fracture heights and densities for each stage of the stimulation. DAS VSP field data from two horizontal wells were acquired and analyzed, with fracture heights and densities consistent with independent fracture diagnostics, such as microseismic. In principle, analysis relies only on P-wave time delays, so it could be applied in real time during stimulation operations. Presentation Date: Wednesday, October 14, 2020 Session Start Time: 1:50 PM Presentation Time: 1:50 PM Location: 361F Presentation Type: Oral
Titov, Aleksei (Colorado School of Mines) | Binder, Gary (Colorado School of Mines) | Jin, Ge (Colorado School of Mines) | Tura, Ali (Colorado School of Mines) | Aaron, Peter (Apache Corporation) | Yates, Mike (Apache Corporation) | Gunnell, Alan (Apache Corporation)
Recent advances in Distributed Acoustic Sensing (DAS) technology allow using DAS for active seismic monitoring of Stimulated Rock Volume (SRV). An inter-stage DAS Vertical Seismic Profiling (VSP) survey was acquired during a zipper-fracturing stimulation. PS-waves scattered by the SRV were observed in the data. They are associated not only with each hydraulic fracturing stage of the well equipped with a fiber-optic cable but also with various stages of an adjacent well. Full wavefield modeling and postprocessing of the field data help us to analyze stage by stage variations in SRV, fracture closure time, and interactions between zipper wells. As a result, we have been able to estimate SRV height in a fiber well, and constraint the SRV height and length for other wells of the zipper group. This information can be extremely valuable in optimizing hydraulic fracturing operations. Presentation Date: Tuesday, October 13, 2020 Session Start Time: 8:30 AM Presentation Time: 8:55 AM Location: 360D Presentation Type: Oral
Summary The 3D hydraulic-fracture-simulation modeling was integrated with 4D time-lapse seismic and microseismic data to evaluate the efficiency of hydraulic-fracture treatments within a 1 sq mile well-spacing test of Wattenberg Field, Colorado. Eleven wells were drilled, stimulated, and produced from the Niobrara and Codell unconventional reservoirs. Seismic monitoring through 4D time-lapse multicomponent seismic data was acquired by prehydraulic fracturing, post-hydraulic fracturing, and after 2 years of production. A hydraulic-fracture-simulation model using a 3D numerical simulator was generated and analyzed for hydraulic-fracturing efficiency and interwell fracture interference between the 11 wells. The 3D hydraulic-fracture simulation is validated using observations from microseismic and 4D multicomponent [compressional-wave (P-wave) and shear-wave (S-wave)] seismic interpretations. The validated 3D simulation results reveal that variations in reservoir properties (faults, rock-strength parameters, and in-situ stress conditions) influence and control hydraulic-fracturing geometry and stimulation efficiency. The integrated results are used to optimize the development of the Niobrara Formation within Wattenberg Field. The valuable insight obtained from the integration is used to optimize well spacing, increase reserves recovery, and improve production performance by highlighting intervals with bypassed potential within the Niobrara. The methods used within the case study can be applied to any unconventional reservoir. Introduction The Niobrara Formation is an organic-rich, self-sourcing unit composed of carbonate deposits in the form of alternating layers of chalks and marls. The Niobrara resource play is typically compared with the Eagle Ford Shale because of its high carbonate content. Early production can be dated back to 1976 from vertical wells in Wattenberg Field, although development was not deemed commercially viable at the time (Sonnenberg 2013). The shale play has become more attractive because of horizontal drilling and multistage hydraulic fracturing, allowing the Niobrara to be developed with overall success in the Denver-Julesburg Basin since 2009. The Niobrara Formation extends into several basins within the central USA involving Colorado, Wyoming, Nebraska, and Kansas.
We discuss the potential use of tube waves generated by perforation (or “perf”) shots as a means of assessing the near-well conductivity for hydraulic fractures, which influences well productivity. These tube waves were recorded on distributed acoustic sensing (DAS) during completion of an unconventional well. The analysis is focused on the perf shots of two sequential stages (11 and 12) and the near-well conductivity of the stages completed prior to each shot (10 and 11), which had the same completion design. We observed much greater tube wave decay within the zone of stage 11 than stage 10. Tube wave decay can be indicative of partial fracture closure, which has often been observed within hours after treatment. Fracture closure results in reduced conductivity, less hydraulic impedance contrast, and lower tube wave decay. We therefore attribute lower tube wave decay in stage 10 to greater fracture closer resulting from the large time delay (>9 days) between the stage 11 perf shot and the end of completion for stage 10. This interpretation is supported by our observations and allows us to evaluate the time component of near-well conductivity stage-by-stage or even cluster-by-cluster and assess completion effectiveness. Presentation Date: Tuesday, October 13, 2020 Session Start Time: 9:20 AM Presentation Time: 10:35 AM Location: Poster Station 2 Presentation Type: Poster
ABSTRACT Distributed acoustic sensing (DAS) technology offers full-well seismic sensor coverage for vertical seismic profiling (VSP) applications. A rapid time-lapse DAS VSP provides the opportunity to record in-situ seismic response between individual fracing stages. An experimental rapid time-lapse DAS VSP was acquired to detect changes in the seismic response following hydraulic stimulation. A traveltime analysis revealed that the direct P-wave arrivals were delayed relative to the baseline and the maximum time-delay was located at the center of the fracturing stage. A slower seismic event in the data showed a much longer delay-time and could be a mode-converted and reflected S-wave below the well. The estimated velocity change from a traveltime simulation showed that the decrease in S-wave velocity could be higher than the P-wave velocity. These observations are investigated further for applications of hydraulic stimulation monitoring and diagnostics. Presentation Date: Tuesday, September 17, 2019 Session Start Time: 8:30 AM Presentation Start Time: 8:55 AM Location: 303B Presentation Type: Oral