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Results
Abstract This study describes the first successful dual-well distributed acoustic sensing (DAS) vertical seismic profiling (VSP) walkaway acquisition in two 4 km deep wells in an onshore desert environment in the Middle East. A dual-fiber interrogator enabled efficient recording of high-channel-count walkaway VSP that was suitable for robust velocity model building and imaging. A good signal-to-noise ratio (S/N) was achieved due to three main factors. First, the fiber cable that was deployed outside the tubing provided good receiver coupling. Second, a gauge length of 24 m was used as a natural receiver array, boosting the S/N. Finally, 16 sweeps per shotpoint were performed using two vibrators in the source array. The selection of optimal acquisition parameters enabled on-tubing fibers to record high-quality seismic signals down to about 4 km. Each shot was recorded by two fibers deployed in wells that are 1.5 km apart. Even with high-quality casing cementation, DAS records exhibited reduced sensitivity/coupling in the shallower section, requiring low-pass filtering for robust first-break picking. The corridor stacks at the two wells show an excellent tie to the surface seismic and agree with the zero-offset VSP geophone corridor stack at one of the wells. A massive ensemble of first-arrival picks enabled multioffset traveltime inversion to reconstruct a reliable velocity profile, approaching the sonic log and overcoming the lower sensitivity of DAS measurement at higher well deviation angles. We used the inverted velocity model to migrate the upgoing reflection response at the two deep onshore wells. The results demonstrate the ability of the dual-well DAS recording to obtain a high-resolution VSP subsurface migrated section with an estimated vertical resolution of about 15 m of reflections down to about 4 km.
- Asia > Middle East > Saudi Arabia (0.47)
- North America > United States > Kentucky > Butler County (0.24)
There is a rising demand for distributed acoustic sensing (DAS) in exploration and developmental geophysics. DAS has several advantages over conventional sensors, for example, fine spatial sampling, wide frequency range, relative ease of permanent downhole deployment. A few examples of using shaped cables were recently presented, which improve the broadside sensitivity of DAS systems. We present a pseudospectral algorithm that can model the seismic gathers acquired with straight and helical cables with DAS systems. The use of an accurate wavefield interpolation technique allows us to obtain synthetic wavefields with fine spatial sampling. The fit-for-purpose strain averaging methodology models the response of shaped fibers and the gauge lengthโs smoothing effect in a consistent manner. We model DAS seismic gathers for surface and borehole seismic acquisitions, examine their properties, and compare them to the more conventional particle velocity recordings.
- Asia (0.30)
- North America > United States > Texas (0.28)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Near-well and vertical seismic profiles (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (1.00)
There have been multiple recent advances in geophysical technologies for application in seismic monitoring for CO2 sequestration: Aramco recently conducted a CO2 enhanced oil recovery (CO2-EOR) monitoring pilot project where 1000 geophones were deployed at a depth of 70 m, which enabled a meaningful interpretation of gas plume geometry. Time-lapse distributed acoustic sensing (DAS) has been proven recently as a viable technology for CO2 monitoring; full-waveform inversion (FWI) and machine learning (ML) methods have become robust and practical tools in multiple applications in general, and in CO2 monitoring in particular. All these advances enable us to see the road ahead in fit-forpurpose acquisition designs for surface and borehole DAS, also leveraging FWI and ML in hybrid workflows for optimizing quality of monitoring vs. cost. To highlight this combination we performed a synthetic survey evaluation design (SED) study based on an experimental setup of the DAS equipped test well in Houston.
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > Asia Government > Middle East Government > Saudi Arabia Government (0.37)
- Reservoir Description and Dynamics > Storage Reservoir Engineering > CO2 capture and sequestration (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Near-well and vertical seismic profiles (1.00)
- (4 more...)
Abstract Land seismic acquisition is moving toward โlight and denseโ geometries, with point receiver systems believed to be an ultimate configuration of choice. Cableless land nodal systems enable more flexible spatial sampling at the price of eliminating even small arrays. For large surveys in a desert environment, such spacing remains insufficient to address the complex near surface, while recordings with single sensors exhibit a significant reduction in data quality. At the same time, exploration problems increasingly demand smaller uncertainty in all seismic products. While 1 m geophone sampling could have addressed these problems, it remains out of economic reach as point sensor cost plateaus. We examine an emerging alternative technology of distributed acoustic sensing (DAS) that revolutionized borehole geophysics but is still mostly unknown in the seismic world. Fully broadband DAS sensors promise massive channel count and uncompromised inline sampling down to 0.25 m. Their distributed nature offers the unique capability to conduct a continuous recording with multiscale grids of โshallow,โ โdeep,โ and โfull-waveform inversionโ receivers, all implemented with a single set of fixed cables and only one round of shooting. These distinct features allow us to simultaneously pursue near-surface characterization, imaging of deeper targets, and velocity model evaluation. Specifically, in a desert environment, distributed sensors may offer superior data quality compared to point sensors, whereas DAS capability of โseismic zoomโ in the near surface becomes instrumental for near-surface characterization. Finally, simultaneous acquisition of surface seismic and vertical arrays that can be achieved easily with DAS can effectively address the exploration of subtler targets such as low-relief structures. We support these findings with a field case study from a desert environment and synthetic examples. With many distinct advantages, surface seismic with DAS emerges as a compelling alternative to modern point-sensor acquisitions.
Adaptive multiscale processing of challenging 3D seismic data for first-break picking, FWI and imaging
Bakulin, Andrey (Geophysics Technology, EXPEC Advanced Research Center, Saudi Aramco) | Silvestrov, Ilya (Geophysics Technology, EXPEC Advanced Research Center, Saudi Aramco) | Dmitriev, Maxim (Geophysics Technology, EXPEC Advanced Research Center, Saudi Aramco)
ABSTRACT We propose an alternative way to achieve multi-shooting grids of low-, mid- and high-frequency sources of comparable signal-to-noise ratio using adaptive summation in processing and conventional high-productivity broadband acquisition. Splitting data into multiple frequency bands provides flexibility to apply variable apertures for enhancement based on local summation. We refer to this as Adaptive Multiscale Processing (AMP). Larger enhancement apertures acceptable for low frequencies enable to compensate for acquisition inefficiency of broadband sources in this range. At mid and high-frequencies AMP efficiently suppresses near surface scattering with a smaller enhancement aperture. We demonstrate that AMP can preserve the signal and deliver reliable first-break picks for tomography, waveforms for full-waveform inversion and data for imaging using field records that are otherwise too low signal-to-noise to be useful. Presentation Date: Wednesday, September 18, 2019 Session Start Time: 8:30 AM Presentation Start Time: 9:45 AM Location: 214D Presentation Type: Oral
Abstract Distributed Acoustic Sensing (DAS), as a seismic sensor, has unique features allowing us to record multiple datasets with variable acquisition parameters set inside the recording box, while using one continuous recording cable and a single round of shooting. We reveal how these distinct features allow DAS to deliver multi-scale data and have the capability to focus on both the near surface and deeper targets simultaneously. We present synthetic and field examples of "deep" and "shallow" DAS surveys and demonstrate their effectiveness. The new capabilities of surface seismic with DAS technology comprise a sensing revolution that addresses long-standing near-surface issues in land seismic without compromising the deeper imaging. Achieving similar capabilities with point sensors could be done but would lead to ballooning acquisition costs, whereas surface seismic with DAS can deliver them at a cost less than conventional geophone acquisition available today.
Abstract A new imaging application is presented using sonic waveform data for ranging to locate a nearby borehole. The challenge of locating a nearby well from a borehole is commonly addressed with electromagnetic (EM) or passive magnetic ranging methods, which can suffer from poor resolution and penetration and require the presence of a conductive or magnetic casing. In addition, the deeper reading active EM methods do not work well when the two boreholes are orthogonal. In contrast, acoustic imaging requires only an impedance contrast between the target object and the surrounding formation, which is adequately provided by the presence of a fluid-filled borehole, even without casing. Here we use acoustic full-waveform sonic data to identify the location, distance, and direction to a target vertical borehole from a nearby highly deviated observation well. The target borehole was located at a distance of about 9 ft with an accuracy of less than 0.5 ft, which was subsequently confirmed by drilling. In addition, acoustic waveform data made it possible to image up to 100 ft above and below the observation well at a resolution comparable to gamma ray and electric logs from the target well.
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Borehole Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Borehole imaging and wellbore seismic (1.00)
Summary Unlike conventional point sensors, Distributed Acoustic Sensing (DAS) has unique features allowing us to record multiple datasets with variable acquisition parameters set inside the recording box, while using one continuous recording cable and a single round of shooting. We reveal how these distinct features allow DAS to deliver multiscale data and have the capability to focus on both the near surface and deeper targets simultaneously. We present synthetic and field examples of โdeepโ and โshallowโ DAS surveys and demonstrate their effectiveness. The new capabilities of surface seismic with DAS technology comprise a sensing revolution that addresses long-standing near-surface issues in land seismic without compromising the deeper imaging.
Advances in near-surface characterization and deep imaging with smart DAS upholes
Bakulin, Andrey (Geophysics Technology, EXPEC Advanced Research Center, Saudi Aramco) | Golikov, Pavel (Geophysics Technology, EXPEC Advanced Research Center, Saudi Aramco) | Smith, Robert (Geophysics Technology, EXPEC Advanced Research Center, Saudi Aramco) | Erickson, Kevin (Geophysics Technology, EXPEC Advanced Research Center, Saudi Aramco) | Silvestrov, Ilya (Geophysics Technology, EXPEC Advanced Research Center, Saudi Aramco) | Al-Ali, Mustafa (Geophysics Technology, EXPEC Advanced Research Center, Saudi Aramco)
Abstract A smart distributed acoustic sensing (DAS) uphole system is proposed that utilizes a cost effective, permanently installed fiber as a seismic sensor embedded in the shallow subsurface. Using this system, uphole velocity surveys for near-surface characterization can be acquired with a single shot by recording all depth levels simultaneously. Dense grids of on-demand smart DAS upholes produce more accurate long-wavelength statics than conventional approaches, reducing uncertainty in the interpretation of low-relief structures. Connecting multiple upholes with a single fiber enables seismic surveys to be acquired with buried vertical arrays. These can provide robust images of the deeper subsurface like surface seismic, but with much improved accuracy due to the elimination of most of the near-surface complexities. The system comprising a carpet of surface shots and a dense grid of smart DAS upholes provides a complete dataset for near-surface characterization as well as imaging for oil and gas exploration of low-relief structures. The proposed smart DAS uphole acquisition scheme was successfully tested on an onshore field in Saudi Arabia. The field test demonstrates the validity of the components and the entire system. Smart DAS uphole data was found to be of excellent quality, while recorded seismic data with buried vertical arrays showed clear reflection signals and produced images of the deeper subsurface. This paper presents the smart DAS uphole system for near-surface characterization and deep imaging, including a discussion of the processing results from the data acquired during the field tests. We show how the novel acquisition system can be used in the petroleum industry to decrease the risks associated with the exploration of low-relief structures.
- Geophysics > Seismic Surveying > Surface Seismic Acquisition (1.00)
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
- Geophysics > Seismic Surveying > Passive Seismic Surveying (0.88)
We demonstrate a novel application of the virtual source method to create shear-wave sources at the location of buried geophones. These virtual downhole sources excite shear waves with a different radiation pattern than known sources. They can be useful in various shear-wave applications. Here we focus on the virtual shear check shot to generate accurate shear-velocity profiles in offshore environments using typical acquisition for marine walkaway vertical seismic profiling (VSP). The virtual source method is applied to walkaway VSP data to obtain new traces resembling seismograms acquired with downhole seismic sources at geophone locations, thus bypassing any overburden complexity. The virtual sources can be synthesized to radiate predominantly shear waves by collecting converted-wave energy scattered throughout the overburden. We illustrate the concept in a synthetic layered model and demonstrate the method by estimating accurate P- and S-wave velocity profiles below salt using a walkaway VSP from the deepwater Gulf of Mexico.
- North America > United States > Louisiana > Salt Field (0.99)
- Europe > Norway > North Sea > Central North Sea > Central Graben > PL 044 > Block 1/9 > Tommeliten Field > Zechstein Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > Central Graben > PL 044 > Block 1/9 > Tommeliten Field > Tor Formation (0.99)
- (6 more...)