基于电阻率约束的分频含气性预测技术

四川盆地二叠系、三叠系礁滩储层气水关系复杂,导致钻井成功率低,部分井不得不侧钻甚至二次侧钻,高精度气水识别成为提高钻探成功率的关键。为此,以该盆地东部T工区二叠系生物礁气藏为例,针对性利用对气水判别敏感的深/浅电阻率信息作为约束,以非线性算法为桥梁,充分挖掘地震资料对含气性敏感的频率信息,再结合全频带相对波阻抗信息,建立深/浅电阻率对数差曲线与地震波形的非线性映射关系,开展储层含气性预测,形成叠后含气性预测方法,并进行了现场应用和效果分析。研究结果表明:①深/浅电阻率指示气层的信息不仅具有验证井作用,而且还可以被提取作为先验信息用于地震资料的约束;②分频信息增大了多元频率数据体与深/浅电阻率对数差的映射关系,有色反演为更加合理的全频带相对波阻抗地震数据,更有利于气水识别;③通过非线性映射关系得到气层敏感因子数据体,量化气层的值域范围,可实现定量的含气性表征。结论认为,所形成的含气性预测技术提供了一种切实有效的叠后含气性预测方法,现场应用效果良好,具有广阔的推广应用前景。

A frequency-divided gas prediction technology based on resistivity constraint

The gas-water relationship in the Permian and Triassic biohermal beach reservoirs in the Sichuan Basin is complex, which results in a low drilling success rate and leads to sidetracking or even secondary sidetracking in some wells. Therefore, high-precision gas-water identification is the key to the drilling success rate. In this paper, the biohermal gas reservoir in the T work area of the eastern Sichuan Basin was taken as an example. Firstly, the frequency information of seismic data sensitive to gas bearing properties was exploited sufficiently by taking the deep/shallow resistivity information which is sensitive to gas-water discrimination as a constraint and the nonlinear algorithm as a bridge. Then, combined with the information of full-band relative wave impedance, a nonlinear mapping relationship between the logarithmic difference curve of deep/shallow resistivity and the seismic waveform was established, and the gas bearing properties of the reservoir were predicted. In this way, a post-stack gas prediction method was developed. Finally, field application and effect analysis were carried out. And the following research results were obtained. First, gas layer information indicated by deep/shallow resistivity not only has the function of verification well, but can be extracted as a priori information for the constraint of seismic data. Second, frequency division information increases the mapping relationship between multi-frequency data volume and the logarithmic difference of deep/shallow resistivity, and the colored inversion, as the more reasonable full-band relative-wave impedance seismic data, is more conducive to gas and water identification. Third, based on the nonlinear mapping relationship, the data volume of a gas sensitive factor was obtained, and the range of gas layers was quantified, so as to realize the quantitative characterization of gas bearing properties. It is concluded that the gas prediction technology developed in this paper provides an effective and practical post-stack gas prediction method, and its field application effect is good, presenting wide popularization and application prospects.