鄂尔多斯盆地安塞地区页岩油地质-工程一体化技术实践

Application of an integrated geology-reservoir engineering approach to shale oil development in Ansai area,Ordos Basin

页岩油是目前国内外油气勘探开发的热点,其地质要素、富集机制与开发特征具有特殊性,实施地质-工程一体化是实现页岩油效益开发的有效举措。采用野外地质调查、岩心观测与采样、测井资料解释、地质与工程参数分析测试等技术方法,在页岩油地质评价方面重点关注岩性、厚度、孔隙度、渗透率、含油饱和度、裂缝发育程度及甜点优选;在工程评价方面针对不同类型甜点,提出适合于鄂尔多斯盆地安塞地区页岩油的开发方式和开发参数。主要认识有:(1)鄂尔多斯盆地安塞地区三叠统延长组7段(长7段)发育典型陆相页岩油,为三角洲前缘和半深湖亚相沉积,源内致密砂岩主要为低孔-超低孔、超低渗储层或非储层,根据地质和力学参数,由好至差储层综合划分为Ⅰ,Ⅱ,Ⅲ和Ⅳ共4类,其中Ⅰ和Ⅱ类储层是甜点目标。(2)长7段页岩油藏依赖储层流体与岩石的弹性膨胀驱动及溶解气驱动,注气补充能量潜力相对有限。针对地质评价优选出的Ⅰ类储层,采用九点法、七点法或交错排状水平井网的准自然能量开发,而Ⅱ类储层采用七点法或五点法水平井网。(3)长7段典型井页岩油水平井初始产量不高,初期递减率较高,后期递减率逐渐降低,生产周期较长,产量相对比较稳定。

Shale oil is a hot spot for petroleum exploration and development over the world.Given its unique geological features,enrichment mechanisms,and development conditions,shale oil is desirable for an integration of geology and reservoir engineering.A variety of technical methods such as field geological survey,core observation and sampling,logging data interpretation,geological and engineering parameter analysis and testing,are applied to geological evaluation of shale oil with focuses on reservoir lithology,thickness,porosity,permeability,oil saturation,fracture development and selection of sweet spots;while in terms of reservoir engineering evaluation,we propose a development method and parameters appropriate to the shale oil in Ansai area regarding the geological characteristics of sweet spots.The main understandings obtained are as follows.First,the 7thmember of the Triassic Yanchang Formation(Chang 7Member)in Ansai area,Ordos Basin is typical of continental shale oil mainly of delta front and semi-deep lacustrine subfacies.The tight sandstones therein mainly belong to reservoirs with low to ultra-low porosity and ultra-low permeability or non-reservoirs.In light of geological and geomechanical parameters,the reservoirs can be classified into4 types from good to poor,including TypeⅠ,TypeⅡ,TypeⅢand TypeⅣ,with the first two types being targets of sweet spots.Second,the flow of shale oil in reservoirs of the Chang 7 Member are driven by reservoir fluid,rocks′elastic expansion and gas dissolution,while the potential of energy supplement via gas injection is limited.For TypeⅠreservoirs selected by geological evaluation,the nine-point,seven-point or staggered horizontal well patterns are used for quasi-natural depletion,while the seven-point or five-point horizontal well patterns are used for development of TypeⅡreservoirs.Third,the typical horizontal wells in the Chang 7 Member is of low initial production with a high decline rate at the initial stage,but the decline rate gradually reduces in the later stages.Moreover,it features a long production cycle with a relatively stable production.