二连盆地低阶煤储层孔隙特征研究——以吉尔嘎朗图凹陷和霍林河凹陷为例

Study on pore characteristics of low rank coal reservoir in Erlian Basin——Taking Jiergalangtu Sag and Huolinhe Sag as example

基于场发射扫描电子显微镜和低温液氮吸附实验,对二连盆地吉尔嘎朗图凹陷和霍林河凹陷下白垩系赛汉塔拉组6口井的煤层样品进行分析。结果显示:研究区煤储层孔隙以原生孔为主,少量气孔,见极少量的矿物质孔及外生孔;孔隙发育以镜质组孔隙为主,其次发育在惰质组和壳质组中,扫描电镜下可观测到矿物质充填其中部分孔隙。孔隙形态以一端或两端开口的楔形为主,部分为具有“双峰”孔隙结构的封闭型和墨水瓶型,吉尔嘎朗图凹陷煤的孔隙为楔型和封闭型,霍林河凹陷煤的孔隙为楔型和墨水瓶型。霍林河凹陷样品的比表面积平均为97.78 m^(2)/g,总孔隙体积平均为0.094 cm^(3)/g,平均孔径为4.98 nm,整体变化范围较小;研究区煤层微孔较为发育且对比表面积贡献最为显著,然后依次为小孔和中孔。吉尔嘎朗图凹陷的低阶煤层样品比表面积平均值为49.75 m^(2)/g,总孔隙体积平均为0.07 cm^(3)/g,平均孔径为11.97 nm,整体变化范围较大;比表面积的主要贡献者为微孔和小孔,中孔的贡献较少。研究区低阶煤层孔隙有利于形成高的含气量,益于煤层气的富集,但气体运移受孔径影响较大,气体难以发生解吸扩散。因此后期煤层气开发阶段应充分考虑其储层孔隙条件,设计有效的储层改造方案,充分调动其储量。

Based on field emission scanning electron microscopy and low temperature liquid nitrogen adsorption experiments,the coal seam samples from six wells of the Lower Cretaceous Saihantala Formation in the Jiergalangtu Sag and Huolinhe Sags in the Erlian Basin were analyzed.The results show that the coal reservoir in the study area are dominated by primary pores,with a few stomata and occasional mineral pores and exogenous pores.These pores are mostly present in vitrinite,a few in inertinite and exinite,and some of them are filled with minerals.The pore morphologies are mainly wedge-shaped with openings at one end or both ends,followed by closed shape and inkbottle-like shape with“double peak”.The pores of Jiergalangtu Sag coal are wedge-shaped pores and closed pores,the coal pores in Huolinhe Sag are wedge-shaped pores and ink-bottle pores.The average specific surface area of the samples in Huolinhe Sag is 97.78 m^(2)/g,the average total pore volume is 0.094 cm^(3)/g,and the average pore diameter is 4.98 nm,with a small overall variation range.The largest contribution of specific surface area is micropores,followed by small pores,and the mesopores have little contribution.The average specific surface area,total pore volume and average pore diameter of the samples in the Jiergalangtu Sag are 49.75 m^(2)/g,0.07 cm^(3)/g and 11.97 nm respectively,with a large overall variation range.Micropores and small pores are the main contributors to the specific surface area,while mesopores contribute little.The pores of low-order coal seam in the study area are favorable for the formation of high gas content and methane storage,but not conducive to gas migration.This increases the difficulty of gas desorption and diffusion.In order to improve the seepage conditions of the reservoir during the development of coalbed methane,it is necessary to design an effective reservoir reconstruction scheme.