不同煤体结构煤储层与煤层气井产出煤粉特征的关系--以鄂尔多斯盆地东缘柳林区块为例

Relationship between coal reservoirs with different coal structures and the characteristics of coal fines produced in CBM wells:a case study of Liulin block at the eastern margin of Ordos Basin

不同类型煤体结构煤储层对煤层气井产出煤粉的影响不同。以鄂尔多斯盆地东缘柳林区块为研究区,为了查明不同煤体结构煤储层分布及其对煤粉产出的影响,基于测井资料构建了主成分分析-支持向量机(PCA-SVM)煤体结构预测模型,应用PCA-SVM模型预测了柳林区块3+4号煤层不同煤体结构煤的分布。根据煤层气井产出煤粉监测和测试结果,分析了煤层气井产出煤粉特征,探讨了煤储层的煤体结构与煤层气井产出煤粉特征的关系。研究结果表明:研究区3+4号煤层煤体结构类型以Ⅱ类煤为主,Ⅰ类煤次之,Ⅲ类煤最少。垂向上,3+4号煤层不同煤体结构煤分层发育,平面上,3+4号煤层的Ⅰ类煤主要分布在研究区中部和东南部,Ⅱ类煤和Ⅲ类煤主要发育在研究区北部和西南部。研究区内的主要构造控制了3+4号煤层煤体结构的平面分布,Ⅰ类煤主要发育在离断层和褶皱较远的构造简单区,Ⅱ类煤主要发育在背斜轴部及伴生断层附近,研究区北部的Ⅲ类煤主要受聚财塔大断层的控制,南部的Ⅲ类煤主要受褶皱和断层双重构造作用的影响。煤体结构类型决定了产出煤粉特征,构造煤是煤粉产出的主要控制因素。不同类型煤体结构煤储层产出煤粉质量浓度大小为Ⅲ类煤>Ⅱ类煤>Ⅰ类煤,Ⅲ类煤对产出煤粉质量浓度起着主导作用,随着Ⅲ类煤厚度的增加,产出煤粉的粒径整体呈现出变小的趋势。不同类型煤体结构煤储层产出煤粉的形态特征不同,Ⅰ类煤产出的煤粉多呈柱状、不规则块状,Ⅱ类煤产出的煤粉多呈块状、球粒状,Ⅲ类煤产出的煤粉多呈片状、薄片状。产出煤粉特征与煤体结构类型具有良好的相关性,因此,可以用煤层气井产出煤粉特征来验证测井判断煤体结构的解释结果。

Coal reservoirs with different coal structures may have different effects on the output of coal fines produced in coalbed methane(CBM)wells.This paper is a case study of Liulin CBM block at the eastern margin of Ordos Basin.To ascertain the distribution of coal reservoirs with different coal structures and its impact on the output of coal fines,the paper establishes a coal structure prediction model based on PCA-SVM(Principal Component Analysis-Support Vector Machine)and log data,and the PCA-SVM model is used to predict the distribution of coal with different coal structures in No.3-4 coal seams of Liulin block.According to the monitoring and test results of coal fines produced in CBM wells,the paper analyzes the output characteristics of CBM coal fines,and also explores the relationship between coal structure and the characteristics of coal fines produced in CBM wells.The results shows that the coal structures of No.3-4 coal seams in the study area are dominated by TypeⅡcoal,followed by TypeⅠand TypeⅢin a decreasing order.Vertically,the No.3-4 coal seams with different coal structures are developed in separate layers.Horizontally,TypeⅠcoal of No.3-4 coal seams is mainly distributed in the middle and southeast of the study area,while TypeⅡandⅢcoals are mainly developed in the north and southwest of the study area.The horizontal distribution of different coal structures in No.3-4 coal seams are controlled by the main structures in the study area.TypeⅠcoal is mainly developed in areas with simple structures far away from faults and folds,while TypeⅡis mainly developed in areas near the anticline axis and associated faults.TypeⅢcoal in the northern part of the study area is mainly controlled by Jucaita fault,while TypeⅢin the southern area is mainly affected by the dual tectonic actions of folds and faults.The type of coal structure determines the output characteristics of coal fines,and tectonic coal is the major controlling factor for the output of coal fines.The concentration of coal fines produced from coal reservoirs with different coal structures is ranked as follows:TypeⅢ>TypeⅡ>Type I.Among them,TypeⅢplays a leading role in the concentration of coal fines.As the thickness of TypeⅢincreases,the particle size of coal fines turns to decrease on the whole.The morphological characteristics of coal fines are different in coal reservoirs with different coal structures.Specifically,the coal fines from Type I are mostly columnar and irregularly massive-shaped,those from TypeⅡare mostly massive and spherulitic,while those from TypeⅢare mostly flake-shaped and sheet-like.In addition,there is a good correlation between the characteristics of coal fines and the type of coal structures.Therefore,the characteristics of coal fines produced from CBM wells can be used to verify logging,and further judge the interpretation results on coal structures.