摘要:
四川盆地南部钻揭茅口组的井数众多,但时间跨度大、资料品质差,可用的取芯资料少,难以满足沉积微相研究的需要。论文以四川盆地南部中二叠统茅口组二段为例,通过仅有的10口井的岩芯观察和薄片分析发现,茅二段A、B、C亚段均存在一套层位稳定的薄层至块状的浅灰-灰色亮晶生屑灰岩构成的生屑滩,并具有多个向上变浅和变粗序列的薄滩体垂向上频繁叠置、单滩体厚度一般较小(小于3 m)、少见同生期暴露等典型特征;伽马测井响应上,该套多旋回叠置的薄滩体呈现总体高背景下的低值的综合响应,因而难以利用测录井资料准确识别和统计颗粒滩的厚度。进一步分析发现,碳酸盐岩台地内部的非暴露浅滩发育时期,颗粒滩发育于微地貌高地、并具有相对更大的沉积速率,因而颗粒滩发育期形成的等时地质体厚度可近似反演沉积期微地貌的相对高低,并在分析等时地质体厚度或沉积微地貌与风化壳岩溶储层发育关系的基础上,指出了区内高能生屑滩主要在泸州-江津、自贡-大足以及青神-资中一线呈带状分布,受控于泸州古隆起雏形和乐山-龙女寺继承性古隆起。结果表明沉积期微地貌恢复对于钻探程度高、资料品质差的盆地老区的沉积微相研究具有重要意义,并对储层预测和深化老层的开发潜力研究具有重要参考意义。
Abstract:
In southern Sichuan Basin, with a number of wells drilled through Maokou Formation, the data obtained is difficult to meet the needs of the study for sedimentary microfacies due to the old materials with poor quality. This paper presents Mao 2A, B, C sub-members all develop a stable bioclastic shoal layer composed of thin stratified-blocky and light gray-gray sparry bioclastic limestones, respectively, which has several typical characteristics:multiple thin shoal bodies with sequences of shallowing and coarsening upwards superimpose frequently in the vertical, the thickness of single shoal body is generally small(less than 3m), the phenomenon of syngenetic exposure is rare through observation and analysis for cores and thin sections of Mao-2 member from only 10 cored wells in southern Sichuan Basin. The Gamma logging character of the multicycle superimposed, thin shoal bodies generally presents the comprehensive response of low value in the high value setting, thus it is difficult to accurately identify and calculate the thickness of grain shoals via logging data. Further analysis found that, during the development of non-exposed shoals inside carbonate platform, the grain shoals develop in microtopographic highs and have a relatively larger deposition rate, thus the depositional microtopographic highs can be approximately portrayed by the thickness variation of isochronal geological bodies that mainly composed of grainstones. Based on analysis of correlation between the thickness of isochronal geological bodies or the depositional microtopography and weathering crust karst reservoirs' development, point out the high-energy bioclastic shoals mainly present along the zonal distibutions of Luzhou-Jiangjin, Zigong-Dazu and Qingshen-Zizhong, which is controlled by the rudiment of Luzhou palaeohigh and Leshan-Longnvsi inherited palaeohigh. The results indicate that the restoration of depositional microtopography has important significance for the study of sedimentary microfacies in highly-developed borehole areas, where the drilling activity has been conducted to a high degree and only low quality of the study material can be used. This may also offer new reference to the prediction of favorable reservoir and the developing potential to the highly development layers.
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