鄂尔多斯盆地中东部奥陶系深层白云岩储集层特征及主控因素

Characteristics and main controlling factors of the Ordovician deep dolomite reservoirs in mid-eastern Ordos Basin

鄂尔多斯盆地中东部奥陶系深层白云岩是天然气勘探的重要目标,但针对该套白云岩储集层的研究相对较少,储集层特征及成因尚不清楚,从而制约了勘探进程。基于此,依据地震、岩心、薄片、测井、物性数据、地球化学特征和CT扫描等资料,笔者对该套白云岩储集层开展了系统研究。结果表明:(1)鄂尔多斯盆地中东部奥陶系深层发育膏溶孔型、颗粒滩型和生物扰动型白云岩储集层,其中膏溶孔型白云岩储集层岩性为含硬石膏结核粉晶白云岩,孔隙由膏模孔和微裂缝组成,平均孔隙度为2.57%;颗粒滩型白云岩储集层岩性为砂(砾)屑云岩、鲕粒云岩和晶粒化颗粒白云岩,孔隙包含粒间(溶)孔、粒内孔、晶间(溶)孔和微裂缝,平均孔隙度为4.65%;生物扰动型白云岩储集层岩性为斑状粉晶白云岩和斑状灰质粉晶白云岩,孔隙为晶间孔和微裂缝,平均孔隙度为2.54%。(2)膏溶孔型和颗粒滩型白云岩储集层的发育主要受沉积相、准同生溶蚀作用和石盐充填作用共同控制,含膏云坪和颗粒滩沉积分别是这两类白云岩储集层发育的物质基础,准同生溶蚀作用是储集层发育的关键,石盐充填作用是储集层致密化的主要因素。(3)生物扰动型储集层发育主要受生物扰动和白云石化作用控制,前者为生物扰动型白云岩储集层发育创造基础条件,后者有利于晶间孔的形成与保存。该研究成果有助于对鄂尔多斯盆地中东部奥陶系深层白云岩天然气的勘探,期望能为下步勘探决策提供技术支撑。

The deep Ordovician dolomite in the mid-eastern Ordos Basin is an important target for natural gas exploration.There are few studies on this set of dolomite reservoirs,and the reservoir characteristics and genesis are unclear,which restricts the further exploration.Based on outcrops,cores,thin sections,loggings,physical property data and CT scanning data,the dolomite reservoir is systematically studied here.The dolomit reservoir of gypsum-dissolved pore type,granular beach type and bio-turbated type developed in deep Ordovician in the mid-eastern Ordos Basin.The gypsum-dissolved pore type reservoir is characterized by anhydrite nodule bearing micro-crystalline dolomite,and the pore is composed of gypsum molds and micro-fractures with an average porosity of 2.57%.The grain-beach dolomite reservoir is composed of calcarenite-rudite dolomite,oolitic dolomite and crystalline dolomite.The pores include inter-granular pores and micro-fractures,with an average porosity of 4.65%.The bioturbated dolomite reservoir is porphyritic micro-crystalline dolomite and porphyritic calcareous micro-crystall dolomite.The pores are inter-crystalline pores and micro-fractures,and the average porosity is 2.54%.Development of gypsum-solution pore-type and grain-beach type dolomite reservoirs was mainly controlled by sedimentary facies,quasi-synchronous dissolution and rock salt filling.The gypsum bearing dolomitic flat and grain-beach facies provided the basis for development of the two types of dolomite reservoirs.The quasi-synchronous dissolution was the key to development of the reservoir,and the rock salt filling was the main factor for densification of the reservoir.Development of bioturbated dolomite reservoir was mainly controlled by bioturbation and dolomitization.Bioturbation createed basic conditions for development of bio-turbated dolomite reservoir.Quasi-contemporaneous dolomitization was conducive to formation and preservation of inter-crystalline pores.The above results are conducive to the exploration of deep dolomite natural gas in the Ordovician in mid-eastern Ordos Basin,and may provide technical support for the further exploration.