Key technologies for complex surface seismic acquisition in the Sichuan Basin and their application effect

Seismic data processing plays a key role in the field of geophysics. The collected seismic data are inevitably contaminated by various types of noise, which makes the effective signals difficult to be accurately discriminated. A fundamental issue is how to improve the signal-to-noise ratio of seismic data. Due to the complex characteristics of noise and signals, it is a challenge for the denoising model to suppress noise and recover weak signals. To suppress random noise in seismic data, we propose a multi-scale deformable convolution neural network denoising model based on U-Net, named MSDC-Unet. The MSDC-Unet mainly contains modules of deformable convolution and dilated convolution. The deformable convolution can change the shape of the convolution kernel to adjust the shape of seismic signals to fit different features, while the dilated convolution with different dilation rates is used to extract feature information at different scales. Furthermore, we combine Charbonnier loss and structure similarity index measure (SSIM) to better characterize geological structures of seismic data. Several examples of synthetic and field seismic data demonstrate that the proposed method is effective in the comprehensive results in terms of quantitative metrics and visual effect of denoising, compared with two traditional denoising methods and two deep convolutional neural network denoising models.

The undulating sand dunes in the Tadong region cause strong interferences in seismic da ta, which leads to poor signal-to-noise (S/N) when targeting the deeply-buried Lower Paleozoic carbonates. With respect to reducing and suppressing this interference from the sand dunes, we present methods for improving the S/N ratio of seismic data, including combining DEM data with a near-surface database for line selection, a point by point sand dune characterized geophone-array elevation difference design, and application of wide-line and a large geophone array together. Combined, these have achieved great improvement in the seismic data quality when applied in the Tadong region.

Developments in marine seismic data acquisition technology have made available streamer systems with 1000 channels and high sampling frequency. The resulting data rates and volumes are above the capacity of the current magnetic tape recording systems. The recording requirements of high rate seismic systems could be met through developments in laser disc technology, in the area of magnetic tape systems or through online pre-processors reducing the amount of data. New recording technologies are essential for the feasibility of high rate seismic systems. INTRODUCTION Industry demand for increased resolution of offshore seismic surveys has resulted in development of more sophisticated acquisition systems. Digital streamers have made possible significant increases in spatial and temporal sampling rates. Some streamer systems provide the possibility of recording up to 1000 channels in addition to high temporal sampling rates. These developments have led to significantly higher data rates than common in marine seismic data recording today. Standard computer readable magnetic tape, which is well known to the seismic industry, is still the state-of-the-art medium for recording of seismic data. Even though this technology has remained essentially the same for several years, it has so far proved to be reliable and sufficient. Unchanged, however~ it will not be adequate for the kind of high rate seismic data recording indicated above. Implementation of new recording technologies is therefore essential to the feasibility and cost effectiveness of high rate seismic acquisition systems The increased recording density and speed requirements of high rate acquisition systems can be met in several ways; through new developments in laser disc technology, in magnetic computer tape technology resulting in magnetic tape systems with higher data rate and density, or through the use of high density digital recorders to seismic data acquisition. Another attractive alternative is to use online pre-processors to perform data reduction to match the recorded data volume to the capabilities of current magnetic tape systems. However, online pre-processing is a large subject which we will leave out of this paper. In this paper we will discuss the use of these recording systems for high rate seismic recording and the status of their development. However, we will begin with a review of some geophysical and operational reasons for using high rate seismic recording. SOME GEOPHYSICAL ASPECTS. Increasing production and development costs of off-shore oil fields have forced many oil companies into careful evaluation of new fields and reevaluation of existing fields currently in production. To meet the required data quality may in some areas require fine spatial sampling intervals of the seismic data, in some cases significantly less than 10 m. The Delphi Survey respondents (Hewitt, 1983) predicted that 25 percent of recording systems in use by 1990 will have at least 1000 channel capability and that this percentage could increase to 50 by 1995.

Seismic data usually contain various types of noise. Noise comes from signal collection environment, equipment (current noise), micro seismic, etc. Noise reduces the signal- to-noise ratio and resolution of seismic records, and affects the accuracy of seismic processing and stratigraphic interpretation. Improving the signal-to-noise ratio of seismic data is the primary task of seismic data processing. In practical research, many algorithms for suppressing random noise interference are proposed. In order to achieve better seismic data denoising technology, this paper introduces a new algorithm: improved shearlet transform algorithm. The basic principle of this algorithm is to perform shearlet transform on noisy seismic data, calculate the L2 norm of shearlet coefficients in different directions at each scale according to the distribution law of effective signals at different scales, and remove random noise according to the adaptive threshold in shearlet domain varying with scale and direction. Note: This paper was accepted into the Technical Program but was not presented at IMAGE 2022 in Houston, Texas.

As the pioneer of shale gas exploration in China, Longmaxi formation that located in the lower Silurian system in Sichuan basin has entered the developing phase. Under the geological background, seismic and multi-exploration wells’ data analysis, it has been proven that the shale gas play in Longmaxi is more complex than it's equivalents in North America. Though the deeper burying depth of Longmaxi has bring extra bonus by higher pore pressure (1.7 to 2.0), Longmaxi is lagging back in some key reservoir quality indicators such as kerogen content and porosity, same time, the compressional tectonic setting and relative active plate movement develop faults and fractures in an unpredictable way brings extra challenge. Driven by the complexity, more and more technologies have been deployed in the development phase to better define the play. Among them, well placement with real-time image, LWD or wireline logging for reservoir quality (RQ) and completion quality (CQ) evaluation and engineering optimized completion design have been recognized as critical steps in better understand shale gas production based on abroad experience. Although it's always appealing to run the integrated methodology with multi-source data for each horizontal well, the tight economic return is preventing field wide implementation. This paper studies multi-well data from an integrated project with PetroChina ZheJiang in Zhao Tong block; examines data acquired from 3 laterals drilled in the same direction in the same pad but utilized different combination of technologies including well placement with real-time image, LWD quad-combo logging with spectroscopy and engineering optimized fracture design. By investigating the micro seismic data and production rate from each lateral, correlation were made to identify the key production drivers and finally lead to the conclusion of the most economic and efficiency technology combination for the horizontal wells development pattern in Sichuan Basin. In conclusion, laterally the heterogeneity of reservoir quality for the same layer in the target platform is not the key production driver. However, reservoir quality and three principal stresses along vertical scope, combining with the nature fracture distribution make a big difference for the completion fracture extension and production rate. As a result, well placement with bedding identification ability being a prevention methodology is quite critical in the mountainous area in Sichuan basin. LWD logging and an engineering optimal completion design based on that provide comprehensive understanding for each lateral should be deployed based on several considerations including well trajectory, heterogeneity, etc. In the early stage of shale gas development of China, utilize the very first block with integrated service to grab the full value of seamless technology and move forward to solve the conflict between the exploration needs and economic return will shed some lights on the development direction in Longmaxi layer.

High Resolution, Simultaneous VSP and Land Seismic Acquisition

Development model and identification of evaluation technology for Wufeng Formation–Longmaxi Formation quality shale gas reservoirs in the Sichuan Basin

The Atlantis ocean bottom seismic (OBS) project applied the technology of deepwater node seismic acquisition in an effort to achieve high-quality subsalt imaging. As the first largescale deepwater seismic acquisition survey to obtain data from autonomous nodes, the survey fostered innovations in node manufacturing, node deployment, and survey design. Over 900 nodes were produced in nine months. Deployment equipment included specially designed skids, two remotely operated vehicles (ROVs), and an advanced navigation system. Intensive modeling provided an initial assessment of optimal node spacing and node layout grid. Further considerations of operational costs, geophysical criteria, and processing requirements led to a final survey design of approximately 6 nodes/km2 in a hexagonal sampling pattern, divided into two patches. The Atlantis OBS project successfully took a complex technology directly from inception to deepwater application, bypassing the gradual progression from shallow to deepwater implementation that has been standard for most deepwater technology. The documentation of lessons learned during the course of the project offers insight not only into how to conduct additional OBS node surveys, but also how to manage a large-scale technologically complex project. Introduction This paper is one of a group of papers 1-5 that collectively describe the development of deepwater ocean bottom seismic (OBS) acquisition technology, a novel technology that is currently (February 2006) being applied at a commercial scale over the Atlantis Field in the Gulf of Mexico. Taken together, these papers present a case history in how a staged development process, rigorously managed, can substantially accelerate the pace of E&P innovation. This case history records the development of this technology from definition of the problem to execution of a large scale field trial. The Atlantis OBS project is unprecedented in directly applying a significant and extensive new technology to the deepwater environment without conducting a lengthy series of shallow water surveys first. Sea trials provided a successful test of the concept on a limited scale (Openshaw and Beaudoin3), and the lessons from the sea trials guided the planning and execution of the at-scale application. This paper traces the execution of the large-scale project from equipment manufacture and survey design to field operations. The scale of the project and the use of innovative technology posed innumerable challenges in system operation and in project execution. Although some of the issues were unique to the Atlantis OBS project, others were characteristic of any large-scale deepwater project. This paper demonstrates that operating a new technology on a large scale requires a stematic and intensive effort. Background The central business challenge that underpinned the Atlantis OBS project was the lack of consistent, high-quality illumination of subsalt reservoirs in the Gulf of Mexico. This problem has made the development of these reservoirs potentially more costly. Determining the number and location of development wells, planning sidetracks, and reservoir modeling are key development activities that will carry higher risk when all or part of a reservoir is poorly illuminated.

PreviousNext No AccessInternational Geophysical Conference, Beijing, China, 24-27 April 2018Application of multi-window dip scanning technique in the fault identification of carbonate rocks of Lower Ordovician, GC areaAuthors: Zhang ErhuaSong YongzhongJu LinboZhang ErhuaExploration and Development Research Institute of Daqing Oilfield Ltd.Search for more papers by this author, Song YongzhongExploration and Development Research Institute of Daqing Oilfield Ltd.Search for more papers by this author, and Ju LinboExploration and Development Research Institute of Daqing Oilfield Ltd.Search for more papers by this authorhttps://doi.org/10.1190/IGC2018-212 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract The reserving space of carbonate which locates in GC area, east of Tarim Basin is mainly secondary porosity, and the reservoir distribution is closely related to faults, so the identification of faults is very important. The vertical distance of strike-slip fault in this area is small and the signal-to-noise ratio of the seismic data is low, which give rise to difficulty to the fault identification inside carbonate rock. On the basis of structure oriented filtering which aims at improving the signal-to-noise ratio of seismic data, this paper uses the multi-window dip scanning technique to identify the characteristics of the faults inside the carbonate rock. Compared with the 3rd generation coherence, this method can recognize the faults with the direction of NNE and NW on the top surface of the limestone effectively and highlights the faults inside carbonate rocks. Keywords: Carbonate insider, Fault identification, Structure oriented filtering, Dip scanning with multi-windowPermalink: https://doi.org/10.1190/IGC2018-212FiguresReferencesRelatedDetails International Geophysical Conference, Beijing, China, 24-27 April 2018ISSN (online):2159-6832Copyright: 2018 Pages: 1821 publication data© 2018 Published in electronic format with permission by the Society of Exploration Geophysicists and Chinese Geophysical SocietyPublisher:Society of Exploration Geophysicists HistoryPublished Online: 11 Dec 2018 CITATION INFORMATION Zhang Erhua, Song Yongzhong, and Ju Linbo, (2018), "Application of multi-window dip scanning technique in the fault identification of carbonate rocks of Lower Ordovician, GC area," SEG Global Meeting Abstracts : 870-872. https://doi.org/10.1190/IGC2018-212 Plain-Language Summary KeywordsCarbonate insiderFault identificationStructure oriented filteringDip scanning with multi-windowPDF DownloadLoading ...

Based on theoretical model and real data of Yongxin area, the paper researches the bin‐divisible processing of high‐density seismic exploration and gets some useful conclusions: 1)In existing conditions of general analog geophones, too small bin(just like 5m×5m, 10m×10m) is not available to increase the S/N ratio of seismic data; 2) When the S/N of a single trace is high, it is very difficult to increase seismic resolution by enhancing fold. 3) For east area of China, the most available fold is 150–300 considering cost performance ratio. Too high density doesn't improve seismic quality in essential.

Seismic data are increasingly required to be high quality for the continuous improvement of the degree of exploration. From the viewpoint of inversion, the utilization of more information is an effective way to improve the signal-to-noise ratio of seismic data. In this letter, we adopt simultaneous sparsity constraints of the first-order differences of signals along the time direction and two spatial directions, described by minimizing the Cauchy function, as a combined constraint (or regularization) term imposed on the time-domain data misfit to propose an inversion-based 3-D seismic denoising method. In this way, the redundancies among time slices and seismic sections along two spatial directions are simultaneously considered, and the edges along the spatial directions can be preserved. Through analyzing the first-order derivative of the sum of the data misfit term and the designed combined regularization term (or the objective function), we derive that the relationship between data and desired signal samples in the range of the first-order neighborhood can be expressed as a linear system with seven data-dependent coefficients. Furthermore, it can be inferred that the sparsity constraints of signal differences along different dimensional directions of 3-D data have some complementary functions of noise reduction and signal preservation. We use a 3-D synthetic data set, a 3-D real poststack data set, and a 3-D real prestack data set to determine that the proposed method is an effective amplitude-preservation denoising tool with an acceptable computational cost.

Ground-roll noise extraction and suppression using high-resolution linear Radon transform

The application of the seismic reflection method to detect stratigraphic changes away from well locations is beginning to gain acceptance among Reservoir Engineers. Unfortunately one of the limitations of this method is the inherent low resolution of seismic data as compared to well log data. Several approaches have been proposed to produce well log-like or pseudo log traces from seismic reflection data. Although there is no improvement in the resolution, the pseudo log traces provide a more convenient way of visually corelating well data to seismic data. A new stratigraphic extrapolation method designed to overcome some of the drawbacks of low resolution is presented. This method consists of relating a model trace (initially derived from well information) to an actual seismic trace by varying the parameters of the model trace within well defined constraints until best match is achieved between them. Extrapolation of the stratigraphy away from the well is performed from trace to trace, the starting model for each trace being determined either from the final model for the previous trace or from an independently postulated model. An interactive computer program is employed for this purpose which allows the incorporation of additional information to the initial model. In this way the final stratigraphic model of the reservoir is the one which best matches the seismic data. Several examples showing the application of the method will be discussed.

Shale gas in China: Characteristics, challenges and prospects (I)

Seismic wave attenuation has strong, negative effect on the seismic data resolution. The high influence of this phenomenon was observed during realization of seismic survey Duza Wolka 3D (Geofizyka Krakow S.A. 2010a). The resolution of recorded seismic data was very low due to high attenuation caused by the Lower Triassic Buntsandstein sandstones. In consequence, interpretation of the thin-layered Zechstein formation is ambiguous. The aim of this paper is to present the multi-stage algorithm for the purpose of minimizing the attenuation effect, hence increasing the resolution of the seismic data. In order to achieve this, the inverse Q filtering process was used. The Q factor (quality factor) was estimated from the vertical seismic profiling data (Geofizyka Krakow S.A. 2010c). To verify the effectiveness of inverse Q filtering, seismic modelling was performed. Results received from seismic modelling gave basis for application the inverse Q filtering on real data. For this operation the seismic time profile inline 112 was chosen from the seismic data set Duza Wolka 3D. Application of inverse Q filtering significantly increased the seismic resolution, which enabled the interpretation of the Zechstein formation with more accuracy.