DETECTION OF GAS IN SANDSTONE RESERVOIRS USING AVO ANALYSIS - A 3-D SEISMIC CASE-HISTORY USING THE GEOSTACK TECHNIQUE
DETECTION OF GAS IN SANDSTONE RESERVOIRS USING AVO ANALYSIS - A 3-D SEISMIC CASE-HISTORY USING THE GEOSTACK TECHNIQUE
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DOI：
10.1190/1.1443695
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发表时间：
1994-09-01
期刊：
影响因子：
3.3
通讯作者：
LEVITT, PR
中科院分区：
文献类型：
--
作者：
FATTI, JL;SMITH, GC;LEVITT, PR
地质叠加技术是一种分析地震振幅随炮检距变化(AVO)信息的方法。分析的结果之一是一组直接的碳氢化合物指示痕迹，称为“流体因素”痕迹。流体因素道被设计为碎屑沉积序列中所有反射层的低振幅，但位于‘’泥岩线‘’之外的岩石除外。泥岩线是纵波速度与S波速度的交叉线，饱和水的砂岩、页岩和粉砂岩位于泥岩线上。位于泥岩线外的一些岩石类型是含气砂岩、碳酸盐和火成岩。在没有碳酸盐和火成岩的情况下，流体因素道上的高振幅反射应该代表含气砂岩。当然，这种关系在自然界中并不完全适用，而且泥石线模型适用的程度因地区而异。然而，它在世界上许多盆地中都是一个有用的模型，包括这里研究的那个盆地。在南非南部大陆架的莫塞尔湾气田上，已经对三维地震数据集进行了地质叠加处理。发现气藏砂岩顶部和底部均有异常高幅度的流体因素反射。绘制了这些流体因素反射的幅度图，发现高幅度值主要局限于钻井确定的气田区域。在储集层相对较厚的地区，发现振幅最高的地区大致位于储集层质量最好(即孔隙度最高)的地区。
The Geostack technique is a method of analyzing seismic amplitude variation with offset (AVO) information. One of the outputs of the analysis is a set of direct hydrocarbon indicator traces called ''fluid factor'' traces. The fluid factor trace is designed to be low amplitude for all reflectors in a clastic sedimentary sequence except for rocks that lie off the ''mudrock line.'' The mudrock line is the line on a crossplot of P-wave velocity against S-wave velocity on which water-saturated sandstones, shales, and siltstones lie. Some of the rock types that lie off the mudrock line are gas-saturated sandstones, carbonates, and igneous rocks. In the absence of carbonates and igneous rocks, high amplitude reflections on fluid factor traces would be expected to represent gas-saturated sandstones. Of course, this relationship does not apply exactly in nature, and the extent to which the mudrock line model applies varies from area to area. However, it is a useful model in many basins of the world, including the one studied here.Geostack processing has been done on a 3-D seismic data set over the Mossel Bay gas field on the southern continental shelf of South Africa. We found that anomalously high amplitude fluid factor reflections occurred at the top and base of the gas-reservoir sandstone. Maps were made of the amplitude of these fluid factor reflections, and it was found that the high amplitude values were restricted mainly to the gas field area as determined by drilling. The highest amplitudes were found to be located roughly in the areas of best reservoir quality (i.e., highest porosity) in areas where the reservoir is relatively thick.