井-震结合泥岩盖层分级评价在乍得D盆地的应用

为定量评价乍得D盆地下白垩统泥岩盖层封闭性能,利用测井资料获取单井泥岩盖层厚度、孔隙度、突破压力等参数,通过分析突破压力与层速度的关系、泥地比与地震属性的关系,明确突破压力和泥岩厚度平面展布特征,建立了以突破压力和泥地比为主要评价参数的评价标准,刻画了D盆地泥岩盖层平面分级特征。结果表明,D盆地Kedeni组泥岩为Ⅰ类和Ⅱ类盖层,Doba组泥岩为Ⅱ类和Ⅲ类盖层,Kedeni组泥岩盖层封闭能力强于Doba组;平面上,北部陡坡带和洼槽带泥岩盖层封闭能力最好,为Ⅰ类和Ⅱ类泥岩盖层发育区,中部低隆带和南部缓坡带次之,以Ⅱ类和Ⅲ类泥岩盖层为主,东北部转换带泥岩盖层品质最差,为Ⅳ类泥岩盖层。该评价结果与实钻吻合良好,表明此评价方法有效,可供类似低勘探程度盆地泥岩盖层封闭性能评价所借鉴。

Grading Evaluation of Mudstone Caprocks Based on Logging-Seismic Combination: A Case Study on D Basin in Chad

In order to evaluate the sealing ability of the Lower Cretaceous mudstone caprock in the D basin in Chad, the thickness, porosity, and break-out pressure of the mudstone caprock are obtained by using well logging data; the relationship between break-out pressure and interval velocity, and the relationship between mud-to-formation ratio and seismic attributes are analyzed; the plane distribution of break-out pressure and mudstone thickness are described; and the evaluation standard for the grading of the mudstone caprock is established by taking break-out pressure and mud-to-formation ratio as primary evaluation parameters. The results show that the mudstone in the Kedeni formation in the D Basin is classified into Type Ⅰ and Ⅱcaprocks, and the mudstone in the Doba formation is Type Ⅱ and Ⅲcaprocks. The sealing ability of the mudstone caprock in the Kedeni formation is stronger than that in the Doba formation. On plane, the mudstone caprocks in the northern steep slope zone and sags have the best sealing abilities, and are ranked as Type Ⅰ and Ⅱ, followed by the mudstone caprocks in the central low-amplitude uplift zone and the southern gentle slope zone, which is dominated by Type Ⅱ and Ⅲ, and the worst mudstone caprock is in the northeastern transition zone, which is Type IV. The evaluation results are in good agreement with the actual drilling results, indicating that the evaluation method is effective and provides a good reference for mudstone caprock evaluation in similar basins with relatively low exploration degrees.