松辽盆地南部德惠断陷合隆-兰家反转带泉一段致密气储层特征及分级评价

开展储层精细评价和分级评价对致密砂岩气资源开发具有重要意义。利用铸体薄片、扫描电镜等实验,从储层岩石学、孔隙类型、成岩演化和储层分类等方面对松辽盆地南部德惠断陷合隆-兰家反转带泉一段致密气储层发育规律及有利储层分布进行研究。结果表明:研究区泉一段致密气储层孔隙以溶蚀的粒间孔、粒内孔为主,物性较差,主体呈低孔-低渗或超低渗特征。成岩演化序列为:①早成岩A-B期,含一定量的高岭石,同时石英次生加大指示发生早期压实作用;②早成岩B期,少许不稳定组分被方解石交代并发生方解石粒间胶结;部分白云石交代早期形成的方解石,形成白云石内方解石的交代残余;③中成岩A期,酸性水体环境会诱发高岭石的沉淀和碳酸盐矿物的溶解;④中成岩B期,沉淀的铁白云石与铁方解石以及石英加大造成孔隙大大降低,后期溶蚀作用较弱,储层致密程度加深。利用K-means聚类方法将研究区泉一段致密储层划分为4类,主要以III类、IV类为主。其中:I类储层主要位于研究区北部和中部,分布范围最小,约占总体储层分布的5%;II类储层在研究区北部,分布范围较大,约占10%;III类储层的分布范围最大,约占60%;IV类储层较II类储层发育,呈连片状、条带状分布,约占25%。

Characteristics and classification evaluation of tight gas reservoirs in the 1st member of Quantou Formation of Helong-Lanjia inversion zone in Dehui Fault Depression

Fine reservoir evaluation and classification is of great significance to the development of tight sandstone gas resources. In this paper,the development regularity and effective reservoirs distribution of tight gas reservoir in the 1 stmember of Quantou Formation of Helong-Lanjia inversion belt in Dehui Fault Depression were ascertained from the aspects of reservoir petrology,pore type,diagenetic evolution and reservoir classification by means of cast thin section and scanning electron microscope. The results show that the porosity of the tight gas reservoirs in the first member of Quantou Formation of the study area is mainly composed of intergranular and intragranular pores,and the porosity is mainly composed of low-porosity and low-permeability or ultralow permeability. The diagenetic evolution sequence is as follows:(1)early diagenetic phase A-B,kaolinite precipitation and quartz secondary enlargement mark the early compaction;(2)early diagenetic phase B,a few unstable components can be metasomatized by calcite and calcite intergranular cementation occurs. Later,some calcite formed in the early period of dolomite metasomatism formed the metasomatism residue of calcite in dolomite;(3)middle diagenetic phase A,environment with acidic water will induce the precipitation of kaolinite and the dissolution of carbonate minerals;(4)middle diagenetic phase B,the precipitation of iron dolomite and calcite,and the increase of quartz will cause great pore reduction,later dissolution is weak,the compact degree of reservoir is strengthening. The k-means clustering method is used to divide the reservoirs in the study area into four categories,of which the III and IV reservoirs are dominant,and the I reservoirs are mainly located in the north and middle of the study area,accounting for about 5% of the four types of reservoirs. The distribution range of type II reservoirs is larger than that of type I reservoirs,accounting for about 10% of the four types in the northern part of the study area. Class III reservoirs have the largest distribution range,accounting for about60% of the four types of reservoirs. The type IV reservoirs which are distributed in forms of sheet and belt-like are more developed than the type II reservoirs,accounting for about 25% of the four types of reservoirs.