胜北洼陷致密砂岩气储层分类方法

Classifying tight sandstone gas reservoirs,Shengbei depression,Tuha Basin

针对吐哈盆地胜北洼陷中侏罗统三间房组储层岩性致密、孔隙度和渗透率低、孔隙结构复杂、纵向非均质性强、油气水同产、储层分类困难等问题,需要明确储层分类方法,为水平井甜点段优选提供技术支撑。通过以岩石物理实验为基础开展储层“四性关系”研究,优选孔隙度、渗透率、粒度中值、排驱压力、核磁T2几何均值、电阻率和声波时差等资料,利用K-means聚类分析方法进行储层分类。研究结果表明:(1)胜北三间房组岩性成熟度中等,黏土和碳酸盐岩矿物填充孔隙空间,强压实作用导致储层致密,孔隙结构变差;(2)三间房组致密砂岩气藏含油气性受储层岩性、物性、孔隙结构和储层非均质性等因素控制,以粒度中值、孔隙度、渗透率、最大孔喉半径、排驱压力、中值压力和电阻率为参数进行聚类分析,将储层划分为Ⅰ、Ⅱ、Ⅲ类;(3)Ⅰ类优质储层岩性为中粗砂岩、分选好、排驱压力和中值压力低,声波时差和核磁T2几何均值大,孔隙结构好;(4)三间房组储层横向连片发育,纵向非均质强,整体以Ⅱ类储层为主,局部Ⅰ类储层发育,Ⅰ类优质储层富集区的水平井体积压裂能获得较高效益。

Gas reservoirs of the Middle Jurassic Sanjianfang Formation in Shengbei depression are characterized by dense lithology,low porosity and permeability,complex pore structure,strong vertical heterogeneity,and simultaneous oil,gas and water production.All these characteristics make reservoir classification challenging.An appropriate classification method is required to support the optimization of sweet spots in horizontal wells.So,reservoir properties were investigated through rock physics experiments.And the porosity,permeability,median grain size,displacement pressure,NMR T2 geometric mean,resistivity,and acoustic time were selected for this classification by using K-means clustering.Results show that(i)Sanjianfang reservoir rocks have moderate maturity,whose pore space is filled with clay and carbonate minerals.The reservoirs become tight due to strong compaction,with deteriorated pore structure;(ii)the hydrocarbon potential in Sanjianfang gas reservoirs is controlled by lithology,physical properties,pore structure and heterogeneity.Based on the clustering analysis with parameters of median grain size,porosity,permeability,maximum pore-throat radius,displacement pressure,median pressure and resistivity,the reservoirs can be classified intoⅠ,ⅡandⅢtypes;(iii)typeⅠ,as quality reservoirs,is composed of medium to coarse sandstone,and exhibits good sorting,low displacement pressure and median pressure,high interval transit time and NMR T2 geometric mean,and good pore structure;and(iv)Sanjianfang reservoirs present continuous extension laterally but strong heterogeneity in vertical.They belong to typeⅡfor the most part,and type I locally.Certain zones developed with type I reservoirs can be efficiently exploited by volume fracturing in horizontal wells.