Seismic Processing Methods Research Articles

Offshore Tech Evolves for Deeper Waters, Deeper Reservoirs

_ Since the late 1930s, the offshore industry has moved from installing the first offshore platform in 14 ft of water to the ultradeepwater 20K era. Advances in seismic, drilling, and development technologies all helped move the industry from shallow waters to ultradeepwaters, from lower-pressure reservoirs to high-pressure/high-temperature (HP/HT) reservoirs, and beyond known hydrocarbon areas like the Gulf of Mexico (GOM) into frontier regions, like Guyana. Brent Gros, vice president of Chevron’s GOM business unit, told JPT there is a stark difference between the GOM of today and how it was when he first started working in the area 26 years ago. Now, he said, operating further from land in water depths of 4,000 to 7,000 ft is the norm. “We’re not really taking crew boats to those platforms, given the distance from shore. We operate as well at much higher pressures,” he said. Jayme Meier, ExxonMobil’s vice president of deepwater project delivery, echoed that sentiment. At the dawn of the offshore era, “anything that was in any amount of water was, by definition, deep water, because it was as far as you could go,” she told JPT. “And we are now at the stage where we are routinely doing things that are in 2000 m (6,560 ft) of water or more, and we continue to press boundaries and technical limits to be able to move further out in water depth.” As such, she said, the fundamental definition of deep water has shifted in the past quarter century. Where To Drill? “To find oil and gas resources, we rely on seismic, and we’ve seen huge advancements in seismic over the past 25 years,” Gros said. 3D seismic technology, pioneered half a century ago, sharpened the view into the world’s reservoirs, and new seismic processing methods have helped identify new opportunities. “Now we have ocean-bottom node surveys, which essentially take a lot of the noise out of surveys, allowing us to image deeper with a clearer image. We also have four-dimensional seismic, which helps us understand the performance of reservoirs through time,” he said. “If you compare the seismic capability today to what we had in the past, it’s like seeing the world with a new pair of glasses, and it really helps us understand potential prospects in a more-complex geological setting and pursue those opportunities in deeper water and deeper horizons than we previously would have been able to.” Deepwater Challenges Moving into ever deeper waters requires more tech and more-capable drilling rigs. It also requires precision, Meier noted. “Technology allows us to position a floating rig on the surface of the ocean. It’s got to be able to drill at very precise angles and precise locations, and significant extensions of technology were needed to enable that to happen. We’re at the point now where we’re even doing multizone completions on our wells in deep water,” she said. point now where we’re even doing multizone completions on our wells in deep water,” she said. She called deepwater “by far the most exciting space” to work in. It requires planning and designing for facilities that must withstand intense, harsh, and constantly changing conditions throughout its lifetime.

Seismic resolution improving by a sequential convolutional neural network.

Thin-bed soft rock is one of the main factors causing large deformations of tunnels. In addition to relying on some innovative construction techniques, detecting thin beds early during surface geological exploration and advanced geological prediction can provide a basis for planning and implementing effective coping measures. The commonly used seismic methods cannot meet the requirement for thin beds detection accuracy. A high-resolution (HR) seismic signal processing method is proposed by introducing a sequential convolutional neural network (SCNN). The deep learning dataset including low-resolution (LR) and HR seismic is firstly prepared through forward modeling. Then, a one-dimension (1D) SCNN architecture is proposed to establish the mapping relationship between LR and HR sequences. Training on the prepared dataset, the HR seismic processing model with high accuracy is achieved and applied to some practical seismic data. The applications on both poststack and prestack seismic data demonstrate that the trained HR processing model can effectively improve the seismic resolution and restore the high-frequency seismic energy so that to recognize the thin-bed rocks.

Quantifying anisotropy parameters in weakly anisotropic media through diffraction traveltime parameter clusters

The seismic response datasets obtained from anisotropic media present several challenges for established seismic processing methods. To determine whether wavefront interference stems from anisotropic effects, velocity model heterogeneity, or both remains a key challenge. While reflection signatures may be insufficient for distinguishing these attributes, diffraction information in seismic datasets often provides richer insights into subsurface structures. In response to these challenges, we propose a framework that explores the feasibility of using diffraction traveltime parameters as indicators of anisotropy. By introducing an average measurement velocity derived from a cluster of diffraction traveltime responses, defined as a function of the traveltime slopes estimated from the dataset, we aim to discern the prevalence of anisotropy, heterogeneity, or both within a target region. Experiments conducted with synthetic data designed to simulate realistic scenarios have yielded promising results.

Seismic high-resolution processing method based on spectral simulation and total variation regularization constraints

Seismic high-resolution processing method based on spectral simulation and total variation regularization constraints

High-resolution seismic processing technique with broadband, wide-azimuth, and high-density seismic data — A case study of thin-sand reservoirs in eastern China

Seismic processing and interpretation techniques provide important tools for oil and gas exploration in the Songliao Basin in eastern China, which is dominated by terrestrial facies. In the Songliao Basin, a large number of thin-sand reservoirs are widely distributed and they are the primary targets of potential oil and gas exploration and exploitation. An important part of exploration in the Songliao Basin is to accurately describe the distribution of these thin-sand belts and the sand-body shapes. However, the thickness of these thin-sand reservoirs is generally below the resolution of conventional seismic processing. Most reservoirs are thin interbeds of sand and mudstones with strong vertical and lateral variations. This makes it difficult to accurately predict the vertical and horizontal distribution of the thin-sand bodies using conventional seismic processing and interpretation methods. In addition, these lithologic traps are difficult to identify due to the complex controlling factors and distribution characteristics and the strong concealment. These challenges motivate us to improve the seismic data quality to help delineate thin-sand reservoirs. We have used the broadband, wide-azimuth, and high-density integrated seismic exploration technique to help delineate thin reservoirs. We first use field single-point excitation and single-point receiver acquisition to obtain seismic data with wide frequency bands, wide azimuth angles, and high folds, which contain rich geologic information. Next, we perform near-surface Q compensation, viscoelastic prestack time migration, seismic attributes, and seismic waveform indication inversion on the newly acquired seismic data. The 3D case study indicates the benefits of improving the imaging of thin-sand body and the accuracy of inversion and reservoir characterization using our method.

A reappraisal of legacy reflection seismic data from the western margin of the Kaapvaal craton, South Africa, with implications for Mesozoic-Cenozoic regional tectonics

The 150 km long, 6 s TWT, 2D seismic profile KBF03A, which was acquired in 1994 and lies near the western edge of the Kaapvaal craton in South Africa, has been reprocessed using standard reflection seismic processing methods. The results exhibit a significant improvement in the imaging quality of the subsurface features and an evident boost in the signal-to-noise ratio. The improved seismic data, combined with application of seismic attributes, integration with surficial geological and geophysical maps, and computation of velocity tomograms, has revealed previously undetected structural features within the supracrustal sequences underlying the profile. In particular, the Phanerozoic sediments found along the profile, comprising exclusively Kalahari Group and Dwyka Group deposits, are disrupted by multiple folds of varying wavelengths (~1–10 km) and variably oriented normal and thrust faults. Additionally, the effect of the Moshaweng fault, previously characterised as a listric fault extending to depths of >10 km, on the Phanerozoic sediments has been further constrained to suggest repeated extensional reactivations and a more recent (<1 Ma) inversion. Considerations of the eastern end of the profile have suggested links between some of the observed structural features and the nearby ~146 Ma Morokweng impact structure, the lateral expanse of which is poorly constrained in the literature. The collection of these newly imaged features is interpreted as evidence for multiple Late Mesozoic to Cenozoic tectonic events, including polyphasic reactivation of basement structures, under both extensional and compressional stress regimes. By analysing these newly detected features, our study not only provides new insight into the neotectonic evolution of the Phanerozoic sediments along the western margin of the Kaapvaal craton, but also demonstrates the utility in reprocessing legacy data and reveals its untapped potential.

Study on reflection spherical wave at the near surface

In real seismic surveys, seismic wave propagates in the form of spherical wave and plane wave is the approximations of spherical wave in the far-field and for high frequencies. The traditional seismic processing and interpretation methods based on the plane wave theory are not exact. Furthermore the difference between the plane wave and spherical wave is strong, especially in the near surface. Studying the characteristics of reflection spherical wave near the surface can develop more accurate wave theory. In this paper, a two-layer model with a high-velocity upper layer is built to analyze the spherical reflection wave characteristics. Tests show when the incident angle reaches a certain level, there will be an irregular wave, the pseudo-spherical wave, following the main reflection spherical wave, which has a great influence on the main reflection wave. This discovery has enriched our understanding of wave propagation theory and it has important guiding significance for accurate study on wave phenomena.

Reprocessed time-lapse seismic data provides new reservoir information on the Njord field

Improvements in time-lapse (4D) seismic processing methods provide opportunities to extract additional information from older time-lapse seismic data sets. This new information can help to optimize reservoir production. Four marine streamer time-lapse seismic data sets on the Njord field, offshore mid-Norway, were previously processed in 2007. Reprocessing in 2020 concentrated on better noise and multiple attenuation, improved imaging, and a focused step-by-step workflow to estimate and correct timing variations within and between surveys. The results dramatically improved on the 2007 processing. Gas injection could be tracked in greater detail and previously unidentified 4D signal was interpreted. The new data sets are expected to enhance reservoir understanding and improve future field performance.

ARCTIC

The article provides an overview and analysis of seismicity within the boundaries of the Arctic region for 2014, a description of seismic station networks and processing methods. The catalog of earthquakes in the Arctic region was compiled on the basis of catalogs of several organizations and seismological centers. In total, 452 earthquakes with ML≥1.5 are included in the earthquake catalog. Most of the earthquakes occurred in 2014, including all the strongest earthquakes, werelocated within the mid-ocean ridges of Mon, Knipovich and Gakkel. In the offshore territories, most of the earthquakes were confined to the Svalbard archipelago, in particular, to the seismically active zone in the Sturfjord strait. The renewal of instrumental seismological observations in 2011 (station ZFI) on Alexandra Land Island in the Franz Josef Land archipelago made it possible to record weak earthquakes in the north of the shelf of the Barents and Kara Seas. For seven earthquakes, the focal me-chanism parameters are presented according to Global CMT catalog.

Passive seismic data primary estimation and noise removal via focal‐denoising closed‐loop surface‐related multiple elimination based on 3D L1‐norm sparse inversion

ABSTRACTPassive seismic has recently attracted a great deal of attention because non‐artificial source is used in subsurface imaging. The utilization of passive source is low cost compared with artificial‐source exploration. In general, constructing virtual shot gathers by using cross‐correlation is a preliminary step in passive seismic data processing, which provides the basis for applying conventional seismic processing methods. However, the subsurface structure is not uniformly illuminated by passive sources, which leads to that the ray path of passive seismic does not fit the hyperbolic hypothesis. Thereby, travel time is incorrect in the virtual shot gathers. Besides, the cross‐correlation results are contaminated by incoherent noise since the passive sources are always natural. Such noise is kinematically similar to seismic events and challenging to be attenuated, which will inevitably reduce the accuracy in the subsequent process. Although primary estimation for transient‐source seismic data has already been proposed, it is not feasible to noise‐source seismic data due to the incoherent noise. To overcome the above problems, we proposed to combine focal transform and local similarity into a highly integrated operator and then added it into the closed‐loop surface‐related multiple elimination based on the 3D L1‐norm sparse inversion framework. Results proved that the method was capable of reliably estimating noise‐free primaries and correcting travel time at far offsets for a foresaid virtual shot gathers in a simultaneous closed‐loop inversion manner.

USE OF SEISMIC SIGNALS' TIME PARAMETERS FOR MOVING OBJECTS RECOGNITION BY REMOTE SEISMIC DEVICES

The aim of the work is to determine improved temporal methods for recognition of a moving person and vehicles and the effectiveness of their use by remote autonomous seismic devices. Currently, the most promising seismic devices for the detection and recognition of moving objects are considered to be devices that use spectral and spectral-temporal methods of seismic signal processing. This is mainly due to their high probability of the objects correct recognition. But the use of these methods leads to a significant increase in the information and energy consumption, which is extremely undesirable for the remote autonomous seismic devices and systems based on them. The article proposes to use the energy-efficient temporal methods of seismic signal processing and the improved recognition methods based on the use of temporal parameters of seismic signals to recognize moving objects in these cases. To implement this and to reduce false alarms of the seismic devices, when animals penetrate into their detection zone, in contrast to the known devices, a temporal selection criterion related to the motion characteristics of medium and large animals is additionally introduced into the recognition method of a moving person. The testing of the recognition methods has shown that the proposed methods allow autonomous seismic devices to have both the insignificant power consumption and a significant value of the probability of the moving objects correct recognition. Compared with spectral, time-frequency and statistical methods for moving object recognition, the proposed temporal methods are much simpler and allow to design the remote autonomous seismic devices with minimal energy consumption.

A towed-type shallow high-resolution seismic detection system for coastal tidal flats and its application in Eastern China

Abstract Restricted by detective equipment and tidal influence seriously, coastal tidal flats are often treated as the transition belt of paralic zone in terms of seismic detection, causing low exploration degree and accuracy in these areas. What is worse, conventional shallow seismic method has a complex system and low acquisition efficiency, which cannot meet the requirements for high-efficiency acquisition in tidal flats. To solve these problems, a towed shallow seismic detection system is specially established for coastal tidal areas, mainly including electric spark source and towable ship-type geophone strings. After comparisons, some advantages of this method are obtained, such as high efficiency, low cost and reliability. Furthermore, its detective accuracy and depth can reach the meter level and more than 800 m, respectively. Then, a series of shallow seismic processing methods are improved for coastal tidal flats. Deconvolution and velocity analysis are emphatically introduced to multiple-wave attenuation. A short array of this towable detection can keep a far more effective wave from being cut off because of its small NMO stretch. Last but not least, the towable method in coastal tidal-flat zones can successfully identify the stratigraphic structure, interface, palaeo-channel, concealed active fault and submarine shallow gas in Jiangsu Coast, Eastern China, which has great practical results and significance for geological and environmental surveys, as well as scientific geo-hazard prevention and mitigation in these areas.

Building realistic structure models to train convolutional neural networks for seismic structural interpretation

Seismic structural interpretation involves highlighting and extracting faults and horizons that are apparent as geometric features in a seismic image. Although seismic image processing methods have been proposed to automate fault and horizon interpretation, each of which today still requires significant human effort. We improve automatic structural interpretation in seismic images by using convolutional neural networks (CNNs) that recently have shown excellent performances in detecting and extracting useful image features and objects. The main limitation of applying CNNs in seismic interpretation is the preparation of many training data sets and especially the corresponding geologic labels. Manually labeling geologic features in a seismic image is highly time-consuming and subjective, which often results in incompletely or inaccurately labeled training images. To solve this problem, we have developed a workflow to automatically build diverse structure models with realistic folding and faulting features. In this workflow, with some assumptions about typical folding and faulting patterns, we simulate structural features in a 3D model by using a set of parameters. By randomly choosing the parameters from some predefined ranges, we are able to automatically generate numerous structure models with realistic and diverse structural features. Based on these structure models with known structural information, we further automatically create numerous synthetic seismic images and the corresponding ground truth of structural labels to train CNNs for structural interpretation in field seismic images. Accurate results of structural interpretation in multiple field seismic images indicate that our workflow simulates realistic and generalized structure models from which the CNNs effectively learn to recognize real structures in field images.

The use of S-guided CREP methodology for advanced seismic structure enhancing processing

To acquire refined seismic targets, the use of more accurate and more precise methods of seismic signal processing is crucial. Novel seismic processing approach is even more important in case of the complex geology of mountainous regions (e.g., Carpathians, Carpathian Foredeep) where sub-vertical layering of varying rock complex can be found, but also in case of old seismic data reprocessing (especially when the signal-to-noise ratio and general quality are low). Regardless of many research papers and significant progress in seismic processing techniques, a properly processed and interpreted seismic image is still hardly affordable for this region. Obtaining a new value in seismic data processing is a core function of the presented research. The use of dip-guided filtering combined with beam partitioned analysis and Z-domain dip analysis for reprocessing of 3D and 2D seismic data from the Carpathians region has been studied.

Using fish lateral line sensing to improve seismic acquisition and processing.

Bioengineering, which studies the principles and design of biological systems, is a field that has inspired the development of several technologies that are currently in use. In this work, we use concepts from the fish lateral line sensing mechanism and apply them to seismic imaging processing. The lateral line is a sensory system composed of an integrated array of mechanical sensors spanning along the fish body. We compare the array of sensors along body fish with the seismic acquisition, which employs an array of equally spaced identical mechanical sensors to image the Earth’s subsurface. In both situations, the mechanical sensors capture and process mechanical vibrations from the environment to produce useful information. We explore the strategy of using the low-pass and high-pass sensors schema of fish lateral line to improve the seismic technique. We use the full-wave inversion method to compare the conventional acquisition procedure of identical sensors with alternative sets of different sensors, which mimics the fish lateral line. Our results show that the alternate sensors arrangement surpasses the performance of the conventional acquisition method, using just half of the input information. The results point at an image processing technique that is computationally more efficient and economical than the usual seismic processing method.

Processing and Interpretation of Time-Lapse Seismic Data at Gao 89 CO2-EOR Area

CO2-EOR greatly recovered oil production in Gao 89-1 block in Sinopec Shengli Oil Company. However, CO2-EOR efficiency was high in some wells but some production wells had little effect. In order to study CO2 sweep efficiency and CO2 distribution, 3D seismic monitoring acquisition was conducted in December, 2010. It is the unique time-lapse 3D seismic datasets to monitor CO2 distribution in China. But the geometry of baseline and monitor is different. Moreover, the depth of reservoir is about 3200 m and effective thickness of reservoir is only 10 m. In addition, the injection volume of CO2 was small and around 50,000 t. If time-lapse 3D seismic technique could discriminate CO2 distribution has been a controversial question. In this paper, we studied the problems during CO2 flooding and estimated the net CO2 storage volume. Then we proposed a time-lapse seismic processing method that improved the conventional geometry degradation and made a better seismic image from vantages of seismic monitoring. In order to calibrate monitoring seismic datasets by using the well log data measured before CO2 injection, P- and S- wave velocity logs versus pressure change method is proposed and verified by making synthetic seismograms. Our study proved that the time-lapse seismic difference mainly caused by the change of pore pressure during CO2 injection in this area. Finally, time-lapse seismic difference calibration method is proposed that assuming the caprock seismic attributes were consistent before and after CO2 injection. The time-lapse difference matched the oil production and CO2 injection well.

Reservoir Prediction Restricted by Sequence Stratigraphy&lt;br/&gt;—A Case Study of Bioclastic Shoal Reservoir in Changxing Formation of Jiannan Area

Bioclastic shoal reservoir in Changxing Formation of Jiannan area is characterized by small thickness and strong heterogeneity. The uncertainty of the reservoir distribution pattern has confined the effective development of this area, so the accurate bioclastic shoal reservoir prediction would be the key to achieve development breakthroughs. Based on drilling, well-log, seismic and core analysis data, this article conducted exquisite sequence stratigraphic classification and established isochronal regional stratigraphic framework of Changxing Formation in Jiannan area. The reservoir seismic corresponding features were determined by exquisite calibrating bioclastic shoal reservoir in Changxing Formation. Therefore, seismic processing methods, such as multiple attribute analysis and amplitude inversion, were applied to attain more reliable reservoir prediction results, which indicated the distribution of vertical reservoir in SSQ2, the IV sequence order and the distribution of horizontal reservoir around Well J43 and JZ1 in the platform margin of the study area.

An introduction to seismic exploration of the Micang-Dabashan foothill belt in the Sichuan Basin

Geologic studies indicate that the platform-margin reef-shallow facies in Permo-Triassic marine strata in the Micang-Dabashan foothill belt in the Sichuan Basin are favorable exploration targets for oil and gas exploration. However, the typical dual-complexity problem (complex surface condition and subsurface structure) brings a great challenge for seismic technology targeting of those potential oil and gas reservoirs. To overcome this problem, varieties of advanced seismic acquisition and processing methods have been used to improve the imaging quality of piedmont seismic data since 2000. Some improvements have been achieved: The reflection waves from the far offset and deep layer can be acquired in shot gathers from limestone outcropped areas, and the signal-to-noise ratio (S/N) of reflection and diffraction waves in the stack section has been enhanced significantly so as to reveal amounts of valuable geologic information. The resolution and the S/N of seismic migration imaging for the strong fold zone in marine strata have been improved partially, so that the structure of the step-fault zone and the enveloping of gypsum rock are clearer than those revealed by the old seismic section. Even so, actual drilling data demonstrate that the subsurface structures of the foothill belt are far more complex than those revealed by the current seismic imaging results. Therefore, postdrilling evaluation for the validity of seismic techniques implemented in the Nanjiang and Zhenba piedmont zone has been carried out. The results indicate that the current acquisition scheme and processing workflow cannot completely fulfill the requirements of high-precision velocity modeling and migration imaging of complex structures (such as footwalls of thrust fault and small-scale fault blocks) in the piedmont zone, especially when the rugged surface and the widespread limestone outcrop appear simultaneously. Finally, we have developed some potential needs of seismic theories and techniques in the foothill belt, including seismic wave propagation, acquisition, and processing technology.

A highly accurate finite-difference method with minimum dispersion error for solving the Helmholtz equation

Numerical simulation of the acoustic wave equation in either isotropic or anisotropic media is crucial to seismic modeling, imaging and inversion. Actually, it represents the core computation cost of these highly advanced seismic processing methods. However, the conventional finite-difference method suffers from severe numerical dispersion errors and S-wave artifacts when solving the acoustic wave equation for anisotropic media. We propose a method to obtain the finite-difference coefficients by comparing its numerical dispersion with the exact form. We find the optimal finite difference coefficients that share the dispersion characteristics of the exact equation with minimal dispersion error. The method is extended to solve the acoustic wave equation in transversely isotropic (TI) media without S-wave artifacts. Numerical examples show that the method is highly accurate and efficient.

Retrieving Low Wavenumber Information in FWI: An Overview of the Cycle-Skipping Phenomenon and Solutions

Full waveform inversion (FWI) is an advanced seismic processing method for high-resolution subsurface geophysical property reconstruction through a data-fitting procedure. When low-frequency seismic data are not available, conventional FWI often suffers from the cycle-skipping issue caused by the severe nonlinearity nature of the standard L2 norm objective function, inducing strong artifacts in the reconstructed geophysical property models.