低勘探程度区煤系致密气水平井地质导向技术及应用——以DJ-P37井区为例

Geosteering technology and application in horizontal wells for coal measure tight gas reservoirs in the areas of low exploration degree:Taking DJ-P37 bore field as an example

在二维地震区、井控程度低及曲流河三角洲前缘沉积等复杂岩性储层中,实施水平井储层钻遇率较低。三维地质模型迭代更新与地质–工程一体化相结合的水平井地质导向技术应用逐渐广泛。鄂尔多斯盆地东南缘上古生界煤系发育山西组山_(2)^(3)亚段北岔沟砂岩等多套致密砂岩储层,其中,大宁–吉县区块砂岩层厚度较薄、纵向岩性复杂、横向变化快、微幅构造发育,基本无出发井且末端井较远(大于1500 m),水平井导向难度大。为了提高低勘探程度区水平井钻探效果,通过标志层识别与厘定、煤岩层对比、资料精准分析与补充、储层顶底特征识别等方法开展研究。首先,总结研究区煤层与炭质泥岩的快速区分方法,解决现场岩性识别困难的难题,构建研究区地层格架;而后,基于测井、地震、地质多种资料的地层精细对比,厘定1个Ⅰ级标志层及3个Ⅱ级标志层,在山_(2)^(3)亚段进一步确定2个Ⅱ级标志层。最后,提出着陆点控制技术、水平段钻遇率提高技术与钻头出层判断方法,形成了三角洲前缘亚相储层水平井地质导向技术。将该技术应用于DJ-P37井区,累计完钻34口,平均砂岩钻遇率78.30%,取得了良好的钻探效果,可为类似区域煤系水平井钻进提供技术借鉴。

In the 2D seismic area,the reservoir with a low well control degree,frontal sedimentary of the meandering river’s delta and other complex lithology reservoirs,the drilling ratio of reservoirs is low when horizontal wells are implemented.The application of the geosteering technology combining the iterative updating of 3D geologic models and geologic-engineering integration has been gradually extensive.Multiple tight sandstone reservoirs,such as the Beichagou sandstone in the Shan_(2)^(3) Submember of the Shanxi Formation,develop in the Neopaleozoic coal measure at the southeastern margin of the Ordos Basin.Among them,the DJ-P37 bore field of the Daning–Jixian Block has the thin sandstone bed,complex longitudinal lithology and fast horizontal change,with the micro-amplitude structure developing;in this bore field,there is generally no departure well,and the end well is in a long distance,resulting in difficult horizontal well steering.In order to enhance the drilling effects of the horizontal wells in the areas with a low degree of exploration,study is implemented by means of marker bed identification and determination,comparison between the coal bed and rock stratum,accurate analysis and completion of data,identification of reservoir top and bottom characteristics,etc.Firstly,the methods for quickly differentiating coal beds from carbonaceous mudstone in the study area were summarized,so as to solve the problem of difficult field lithology identification and build the stratigraphic framework in the study area.Secondly,on the basis of the meticulous stratigraphic correlation of multiple logging data,seismic data and geological data,one ClassⅠmarker bed and three ClassⅡmarker beds were determined;two ClassⅡmarker beds were further determined in the Shan_(2)^(3)Submember.Finally,the technology of landing site control,the technology of improving the drilling ratio in horizontal sections and the method of determining whether a bit penetrates reservoirs were proposed,forming the geosteering technology for horizontal wells in delta’s frontal subfacies reservoirs.The technology was applied in the DJ-P37 bore field,and accumulatively 34 wells were completed,with 78.30% of the average drilling ratio in the sandstone,providing good drilling effects.The application can provide technological references for the coal measure horizontal well drilling in similar areas.