元坝须三段致密含钙砂砾岩地层测井响应特征及岩性识别方法

致密含钙砂砾岩地层岩石类型多样,含钙屑砂岩、岩屑砂岩、炭质砂岩、砂砾岩等,然而含钙砂砾岩地层不同岩石类型测井响应差异小、识别难,岩性识别成为制约该类储层有效勘探开发的关键.以多级交会图为手段,详细分析各岩石类型测井响应特征及差异的内在成因,确定各岩石类型在测井交会图上的分布区间,实现岩性逐级判别.首先将含钙砂砾岩地层岩性分为煤、泥岩、砾岩、砂岩四大类,采用电阻率、伽马等测井方法识别四大类岩性;然后,根据砾石含量将砾岩分为含砂砾岩、砂质砾岩两小类,采用电阻率、中子等测井方法对砾岩进行细分;接着,根据组分及粒度将砂岩划分为炭质砂岩、中-粗粒钙屑砂岩、细粒钙屑砂岩、钙屑粉砂岩-常规岩屑砂岩四小类,采用电阻率、伽马等测井方法对砂岩进行细分;最终实现基于多级交会图的含钙致密砂砾岩地层四大类八小类岩性识别,识别结果与岩心、薄片吻合较好.该方法为明确致密含钙砂砾岩地层各类岩性测井响应特征、建立岩性剖面及确定有利储层展布提供了依据.

Well Logging Characteristics and Lithology Identification Methods of Tight Calcarenaceous Sandy Conglomerate Reservoirs of The 3rd Member of Xujiahe Formation in Yuanba Area

There are various rock types in tight calcarenaceous sandy conglomerate reservoirs which includes calcarenaceous sandstone, lithic sandstone, carbonaceous sandstone, conglomerate, and mudstone. However, there is little difference in logging response between different rocks types and they are difficult to be identified. The identification of different rock types of tight calcarenaceous sandy conglomerate formation has become a key factor restricting the exploration and development of the reservoir. In order to solve the problem, the log response of different rock types and their differences internal cause were analyzed in detail based on multi-level cross-plots, and the distribution areas of different rock types on the cross-plots were determined. Firstly, the rock types of calcarenaceous sandy conglomerate reservoirs were divided into four categories: conglomerate, sandstone, coal and mudstone, and the resistivity, gamma and other logging methods were used to identify these four rock types. Secondly, according to the gravel content, the conglomerate was divided into two small classes: sand-bearing conglomerate and sandy conglomerate, and the resistivity, neutron and other logging methods were used to subdivide the conglomerate. Thirdly, sandstone was divided into carbonaceous sandstone, coarse-medium-grained calcarenaceous sandstone, fine-grained calcarenaceous sandstone, calcarenaceous siltstone&conventional lithic sandstone according to its composition and granularity, and the resistivity, gamma and other logging methods were used to subdivide the sandstone. Finally, the identification method of four categories and eight small classes was established based on multi-level cross-plots, and the identification results were in good agreement with core and thin sections names. This method provides a sound basis for clearly understanding the logging characteristics of each rock type of tight calcarenaceous sandy conglomerate formation, establishing the lithology profile, and determining the favorable reservoir distribution.