Rapid Sinusoidal Fitting Method for Near-Bit Gamma Imaging While Drilling
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摘要:
针对现有随钻测井数据传输速率较低的问题和井下实时获取伽马成像图的需求，模拟分析了近钻头伽马成像测井仪器穿过倾斜界面进入高放射性泥岩层的扇区成像特征，提出了基于扇区伽马成像图的快速正弦曲线拟合方法。设计了近钻头伽马成像测井中的快速正弦曲线拟合固件算法，将最小二乘估计算法和三参数正弦拟合相结合，提取得到正弦曲线的幅度、频率、相位和直流分量等4个参数，为拟合反演形成多扇区伽马成像图提供数据。利用快速正弦曲线拟合方法，测试了用标准岩样构造分层倾斜地层模拟井眼采集的伽马数据，实现了多扇区伽马成像测量值的拟合，且拟合误差较小。研究结果表明，拟合反演得到的8扇区伽马成像图的正弦曲线特征明显，能够准确反映倾斜地层界面信息，验证了快速正弦曲线拟合方法的可行性和正确性。
Abstract:Seeking to solve the problem of low transmission rate of existing LWD data and the demands on real-time gamma imaging, sector gamma-ray imaging characteristics were simulated and analyzed. This occurred while a near bit gamma-ray imaging tool crossing inclined interface moving from low-level radioactive sandstone to high-level radioactive mudstone, and thus a rapid sinusoidal fitting method based on the sector gamma imaging was proposed. Based on the studies, a rapid sinusoidal fitting firmware algorithm for near-bit gamma imaging logging was designed. This algorithm combined the least squares frequency estimation and 3-parameter sine fitting to obtain the 4 parameters of the sinusoid, such as amplitude, frequency, phase and DC component, hence obtaining the multi-sector gamma imaging through fitting inversion. By using the fast sinusoidal fitting method, the gamma data was acquired in the simulated wellbore fabricated with the standard rock samples and layered dipping strata, and the fitting of multi-sector gamma imaging measurement was realized with a small fitting error. The results showed that the sinusoidal features of the 8-sector gamma image obtained by fitting inversion were clear and they could accurately reflect the information of the inclined strata interface, which verified the correctness and feasibility of the fast sinusoidal fitting method.
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Keywords:
- logging while drilling /
- gamma-ray imaging /
- near bit /
- sector /
- inclined interface /
- sinusoid /
- fitting method
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图 1 充满液体井眼倾斜界面地层模型
Figure 1. Inclined interface stratigraphic model with liquid-filled wellbore
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图 4 仪器下短节DSP控制及数据处理流程
Figure 4. DSP control and data processing workflow of instrument below the sub
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图 5 伽马测量值快速正弦曲线拟合流程
Figure 5. Rapid sinusoidal fitting process for gamma measurement value
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图 6 用标准岩样构成的分层倾斜地层井眼模型
Figure 6. Layered dipping strata wellbore model fabricated with standard rock samples
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