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Summary The maturing fields in the east of China have been in a high degree of prospecting, almost covered by 3-D exploration. At present, we use multiple-block-jointed static correction to do multi-survey joint processing, without considering the effects of the time-variant near-surface structure on the seismic data. Focusing on the time-variant near-surface structure, this paper introduces model analysis and forward model processing, and puts forward a new method of static correction for multi-survey joint processing in areas where the time-variant near-surface structure changes greatly. Problem posing 3-D exploration has been carried out in maturing fields in the east of China since 1980s. Almost all favorable structural belts have been covered by 3-D exploration. In North China where the economy developed quickly, a large amount of groundwater is regarded as a necessity in industry and agriculture. As a result, the water table lowered quickly, and the amplitude reaches several meters to ten-plus meters, forming a large funnel of the water table (Fig 1, Table 1). The reasons for this phenomenon lie as follows: the water resource per capita in these areas is only 335m3 per year, less than one sixth of the national average. Moreover the surface water distributes odds in space-time, which results in the surface water becoming an important part of both the economic and social sustainable development in these areas. At present, the groundwater is more than seventy percent of the entire water resource consumption in Beijing, Shijiazhuang, Xingtai, Handan, Baoding, Hengshui, Langfang and Tangshan, for example. Ever since the 1960s, North China began large scale exploration of the underground water supply. The number of electro-mechanical wells has soared from 1800 in the 1960s to 700,000 in 1997. At the same time, the annual yield of the shallow groundwater is rising from 791.3×104 in the 1970s to an average of 1057.9 from 1985 to 1997. Long-term over-exploration of groundwater causes the underground water level to descend at average of 0.5-1.0 meters every year (Figure 2). In the past 50 years, a unified circulation system of ground water in North China Plain is changing into a new model which mainly features vertical movement in local regions. As a result, in space it forms funnels of groundwater with different sizes and different ranges while in the form of time, it shows variation with depth. Due to the constant changes in the time variation of surface structure, static correction acquired in different years shows a large difference, which results in failing to close. The current method uses the newest 3-D data of surface structure and refers to the data acquired in the past, to build a unified model of surface structure. We think that the time variation of surface structure can be solved by statics. However, in those regions where the time variation of the surface structure changes greatly, it is difficult to settle the problems by statics. An analysis of joint processing in the time variation regions of surface structure In order to process the 3-D seismic data conveniently, the current method is to build a unified model of surface structure by smoothing the 3-D surface data collected in different years.
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
Application of 3D-3C Seismic Exploration In Saihantala Lithologic Reservoirs
Xuefeng, Zou (BGP, CNPC) | Zhiwen, Deng (BGP, CNPC) | Shitian, Cui (BGP, CNPC) | Yong, He (BGP, CNPC) | Xuming, Bai (BGP, CNPC) | Xiangyu, Guo (BGP, CNPC) | Jiushuan, Wang (BGP, CNPC) | Chuanzhang, Tang (BGP, CNPC) | Haidong, Li (BGP, CNPC)
Summary The ongoing exploration in the Saihantala Depression has been focused on lithologic reservoirs. It is difficult to reduce ambiguity and to assess uncertainty in seismic lithology discrimination and fluid type identification using conventional compressional wave (P-wave) exploration. A three dimensional, three component (3D-3C) seismic survey with P-wave source and 3C geophones has been performed in the study region, taking advantage of combining P-wave and converted wave (C-wave or PS-wave) exploration. Instead of using vibroseis, a dynamite source is used to improve the signal-to-noise (S/N) ratio and bandwidth of the C-wave data. High quality C-wave imaging has been achieved using four-parameter velocity analysis and anisotropic pre-stack time migration (PSTM). Sedimentary facies have been well discriminated using the obtained Vp/Vs ratios in the target layer. Our study shows that the combined exploration method effectively characterizes the lithologic reservoir. Introduction Since the 1990s, 3D exploration has been carried out in the main area of the Saihantala Depression, located in the Inner Mongolia. The inferior technology and equipment used in exploration resulted in poor quality seismic profiles with insufficient resolution for recognizing lithologic traps or predicting lithologic stratigraphic reservoirs. Therefore 3D-3C, a more advanced technology, is needed in seismic exploration in the Saihantala region. 3D-3C exploration makes use of P-wave and C-wave data together to improve the accuracy of reservoir predication, structural imaging, lithology identification, and fluid detection. In this study the Saizhong Sag of the Saihantala Depression is selected to apply the 3D-3C exploration survey. High-quality P-wave and C-wave data have been achieved using 3C seismic data acquisition, processing, and interpretation. Data acquisition To ensure the uniform distribution of CCP fold coverage and offsets, the following geometry is used: a 12-line, 6-shot, 234 trace oblique pattern with a bin of 20m×20m, 78 coverage, small rolling interval of scroll one line, and 4,875 m long spread. Dynamite is used as the source, improving S/N ratio and bandwidth of the obtained C-wave data, compared with traditional vibroseis (Figure 1). Conducting a multiwave uphole survey to investigate P and S wave near surface parameters, C-wave statics were calculated correctly, and a precise surface structure was obtained. Data processing C-wave data processing features a four parameter velocity analysis and anisotropic PSTM technology. The obtained C-wave data and resulting C-wave imaging are dramatically improved. Due to the approximate nature of the calculation of the common conversion point (CCP) of C-wave data, and due to the fact that C-wave dip moveout (DMO) is strongly velocity-dependent, the C-wave PSTM method is used to avoid the CCP calculation and to improve C-wave imaging. C-wave anisotropic PSTM can be calculated as follows: Data interpretation With P and S wave joint interpretation, sedimentary facies have been well discriminated using the obtained P and S wave velocity ratios in the target layer. P and S wave joint inversion clearly identifies the lithologies of reservoirs. P and S wave velocity ratio (gamma) can be estimated using different approaches. 1) Layer method This is the most common method. If there are more than two layers identified in the PP and PS wave seismic profiles, gamma would be calculated in the corresponding layer.
- Asia > Mongolia (0.24)
- Asia > China > Inner Mongolia (0.24)
- North America > United States > Kentucky > Butler County (0.24)
- Geology > Geological Subdiscipline > Stratigraphy (0.54)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.34)