Liu, Ning (Liaohe Oilfield, CNPC) | Zhang, Yan (Liaohe Oilfield, CNPC) | Wang, Guodong (Liaohe Oilfield, CNPC) | Xin, Kunlie (Liaohe Oilfield, CNPC) | Wang, Xiaodong (Liaohe Oilfield, CNPC) | Zhao, Zihan (Liaohe Oilfield, CNPC) | Zhao, Fan (Liaohe Oilfield, CNPC) | Zhang, Jing (Liaohe Oilfield, CNPC)
D block is a heavy oil reservoir that was first developed in 1997 with the method of Cyclic Steam Stimulation (CSS). After nearly 20 years’ development, several technical challenges have shown: the reservoir pressure decreased from 7.4MPa to 2.9MPa, and the Steam Oil Ratio (SOR) increase from 2.86 to 3.56. As a result, the traditional CSS method seems to be uneconomic.
In view of the problems shown above, CO2 assisted CSS was tested in this oilfield and has shown great success as follow: The steam injection pressure increased from 5.7 MPa to 6.9 MPa and the SOR decreased from 3.45 to 2.86. Besides the underground success, CO2 was separated from the associated gas and then reinjected into the reservoir. This process can reduce the emission of CO2 so that it is both a economic and green method. In addition, according to the field performance, this paper seeks to establish a better understanding of the possible mechanisms involved in the CO2 assisted CSS.
Cui, Dong (Research Institute of Petroleum Exploration & Development, PetroChina) | Hu, Ying (Research Institute of Petroleum Exploration & Development, PetroChina) | Zhang, Yan (Research Institute of Petroleum Exploration & Development, PetroChina) | Zhang, Cai (Research Institute of Petroleum Exploration & Development, PetroChina) | Zhang, Yujie (Institute of Geology and Geophysics, China Academy of Sciences)
Near-surface velocity model is the key issue to seismic imaging and static correction. It has becomes a broad consensus that it is velocity model, not imaging algorithm, determines the quality of image. Waveform tomography or FWI is a powerful tool to obtain underground velocity. However, the application of waveform tomography has some obstacles. One of the biggest problems that prevent the application is the non-linear waveform misfit function. Correlation-based first arrival travletime tomography could obtain highly accurate velocity model in complex structure district using cross-correlation misfit function, and even don’t need to pick first arrival time or wavelet. Though this method appears to provide less model resolution compared to waveform tomography, this method could work well in those places traditional ray-based tomography may fail because of the high velocity layer exposing to the ground. Theory and numerical example indicate that this method could accurately perform near-surface velocity modeling and has a broad application prospect.
Presentation Date: Wednesday, October 17, 2018
Start Time: 1:50:00 PM
Location: Poster Station 22
Presentation Type: Poster
The aim of the present paper is to investigate the ultimate strength assessment method of stiffened plates with grooving corrosion damage under uniaxial compression. A series of nonlinear finite element analyses has been conducted to investigate the effect of grooving corrosion, including the depth and width of corrosion, the location of corrosion and the ratio of the corroded volume loss of stiffener to that of plate. Based on the relative parameters (such as slenderness of the stiffened plate, aspect of the plate) examined to determine the influences of the stiffened plates on the ultimate strength, the ultimate strength reduction formula of stiffened plates subjected to weld-induced grooving corrosion was derived by data analyses. Research shows, this derived formula can be used to evaluate the ultimate strength of stiffened plates with grooving corrosion.
Worldwide, aging of ships is increasingly serious and ships are in a high salinity environment for a long time, so hull structures are at high risk of corrosion during ship service. Corrosion is the chemical reaction of metal to its surrounding environment, and it would lead to degradation of performance of the hull structure, such as the ultimate strength, operational life-span of ship, the navigation safety, etc. Therefore, evaluating the ultimate strength of corroded marine structures plays a critical role during ship service.
Corrosion is mainly divided into general corrosion and local corrosion and local corrosion is divided into pitting corrosion and grooving corrosion, viewed from the point of the ship corrosion form. Uniform corrosion occurs on the surface of the entire structure, resulting in a uniform reduction of the metal thickness. Pitting corrosion, where there is many pits with different depth, occurs on the local area while the rest of the area does not corrode or slightly corrode. Groove corrosion normally takes place adjacent to welds and is of particular concern for the connection of side frames to shell plate in single skin bulk carriers. So far, the study of the effects of uniform corrosion and pitting corrosion on the ultimate strength of hull structures is relatively mature. but there are still many problems to be solved for the influence of grooving corrosion on the structural strength.
The modularized design and construction philosophy is a common practice for large onshore and offshore projects due to its opportunity for schedule and cost-savings. Multiple modules are fabricated at different construction yards across the world and then transported to service sites by marine transportation vessels. During transportation, the seafastening system is required to secure modules on transportation vessels. The seafastening system is designed to support the forces imposed on the module by accelerations, motions and deflections of the vessel, and distribute the concentrated forces from the module onto the vessel. The system reliability will depend highly on the forces for which the seafastening is designed.
The determination of the forces is typically based on decoupled analysis where the module and vessel are analyzed separately. The resulting forces are usually over-conservative. However, this paper presents a more advanced and accurate approach where interaction FE analysis is utilized to calculate the reaction forces. A light weight seafastening system is designed based on the calculated reaction forces. The system consists of a series of grillage beams with stoppers and wing plates welded to the vessel deck. Additional clips are used to restrain the module uplift. The proposed design allows for an easy and efficient seafastening removal, an optimum use of the vessel capacity and a reduction in fabrication costs. Results from a sample seafastening design are presented.
Due to the absorption of the formation, the frequency band of seismic wave narrows in the process of propagation and the resolution decreases. Spectral modelling deconvolution improves the resolution of seismic data by fitting the wavelet amplitude spectrum and applying zero-phase deconvolution on the seismic signal. Considering the different frequency components of seismic data from different depths, compensating the spectrum differently according to the depth of seismic data is meaningful, in which the time-frequency spectrum is needed. Recently proposed time-frequency analysis method named Synchrosqueezed Wavelet Transform (SSWT) is superior to the traditional time-frequency analysis method in time-frequency resolution, which has been applied to seismic data processing and interpretation. In this paper, we propose a method named Time-Varying Spectral Modeling Deconvolution Based on SSWT and apply it to seismic data to improve the resolution. The effectiveness of the proposed method in improving the resolution is verified by testing field data and comparing it with the results based on Generalized S-transform.
Presentation Date: Thursday, September 28, 2017
Start Time: 9:45 AM
Presentation Type: ORAL
In fractured reservoirs, seismic wave velocity and amplitude depend on frequency and incidence angle. The frequency dependency is believed to be principally caused by the wave-induced flow of pore fluid at the mesoscopic scale. In recent years, two particular phenomena, partial saturation and soft fractures, have been identified as significant mechanisms of wave induced flow. However these phenomena are usually treated separately. Recently a unified model was proposed for a porous rock with a set of aligned fractures filled with arbitrary fluid. Existing models treat waves propagating perpendicular to the fractures. In this paper, we extend the model to all propagation angles by assuming that the flow direction is perpendicular to the layering plane and is independent of the loading direction. We first consider the limiting cases through poroelastic Backus averaging, and then we obtain the full stiffness tensor of the equivalent TI medium. The numerical results show that when the bulk modulus of the fracture-filling fluid is relatively large, the dispersion and attenuation of P-waves are mainly caused by soft fracturs. While the bulk modulus of fluid in fractures is much smaller than that of matrix pores, the attenuation due to the ‘partial saturation’ mechanism dominants.
Presentation Date: Wednesday, October 19, 2016
Start Time: 9:15:00 AM
Location: Lobby D/C
Presentation Type: POSTER
Summary Multi-wave seismic exploration, which utilizes P-wave, S-wave and PSwave, is an effective method for the fine exploration of petroliferous basin and for hydrocarbon prediction. In PSwave PSDM, the fact that a reflector of both P-and PSwaves has same depth in depth domain is used in reflection correlation and data interpretation. This fact can also help with imaging accuracy and geological interpretation. This paper presents a PSwave PSDM processing flow, including depth domain velocity model building. Using this flow, we obtained better imaging results in terms of higher accuracy and resolution.
Frequency slice wavelet transform (FSWT), a new timefrequency signal analysis method proposed by Zhonghong Yan et al. (2009), has some new properties compared to continuous wavelet transform (CWT). FSWT has been successfully used to process and analyze mechanical vibration signals. In order to test this new transform’s advantage, we try to study reservoir attenuation characterization by FSWT time frequency analysis. In the first step, we will calculate the center of gravity in the seismic signal frequency domain (CGF) and then recognize CGF parameter as a discriminant criterion for FSWT aimed to control the frequency resolution ratio of the seismic signal, which means we could apply the self-adaptive FSWT to seismic signal. After that, the arguments of gradient and intercept will be obtained from the point spectrum in the FSWT time-frequency domain, which is available to research the reservoir characterization. At the end, the Marmousi II model and real data will be utilized to test and verify the effectiveness of the algorithm.
Fourier transform could provide global information of frequency of stationary signal but is incapable of supplying local frequency variation about the non-stationary signal. Seismic signal has the unsteady and nonlinear characteristics which are expressed by the statistical variation in space and time domain and Many methods have been popularly adopted to analyze seismic signal including short-time Fourier transform (STFT), CWT, Wigner Ville Distribution (WVD), S-transform (ST), Hilbert-Huang Transform (HHT), Local time-frequency decomposition (LTFD) and Matching pursuit (MP). All these spectral decomposition methods could convert seismic signal from one dimensional time domain to two dimensional time frequency domain, which provide more information and illustrate more features which couldn’t be found in time domain representation. Nevertheless, these methods have some limitations in the practice. Take STFT as an example, as long as the window function is determined the time-frequency resolution will be limited. WVD has the well-known drawbacks including cross-term interference and aliasing, which contaminates the achieved high resolution. The MP method contains several parameters and is a relatively expensive and timeconsuming method.
Seismic AVOA method, which employs P-wave amplitude variation with incident angle and acquisition azimuth, is a powerful tool for fracture characterization in HTI medium. However, this azimuthal AVO based fracture characterization approach is only applicable to fracture set with single dominant orientation, which is not always true in real applications. Ant tracking is able to delineate small scale discontinuities, which has a close relationship to fractures. Curvature is also a popular method for fracture characterization. In this paper, we perform fracture characterization by comprehensively utilizing azimuthal AVO, ant tracking and curvature analysis. We select optimal incident angle range for azimuthal AVO based fracture inversion. To make full use of wide azimuth seismic data, we perform ant tracking on six azimuthally sectored seismic volumes and then combine the results together to better delineate fractures set with multiple orientations. Curvature attribute is also introduced as a useful aid to AVOA and ant-tracking for fracture characterization. We applied this integrated fracture characterization scheme to Tarim Basin, Northwest China. Application results showed that there is a good accordance in the results produced by AVOA, multi-azimuth seismic volume ant-tracking, and curvature. The estimated fracture orientation was verified by image log data. These results indicate that the proposed method is effective in fracture characterization.