强非均质碳酸盐岩气藏储层组合模式对气井产能的影响

Effects of reservoir combination in carbonates with strong heterogeneity on productivity

四川盆地安岳气田深层海相碳酸盐岩已发现震旦系、寒武系、二叠系等多套主要产层,埋深4600~5200 m,非均质性较强。其中震旦系灯影组四段台内气藏储层厚度相对较薄,纵向多层叠置,整体表现为低孔隙度、低渗透率,而构造形成的有效裂缝、岩溶作用形成的溶蚀孔洞改善了局部储层品质。基于孔洞缝搭配关系及其成因,将储层划分为裂缝-孔洞型、孔洞型、孔隙型等3种类型。不同储层类型因孔喉结构与缝洞系统发育规模的差异,表现出特殊的复杂渗流特征。利用数值模拟将3种类型储层按照不同的组合方式进行气井生产模拟,研究结果表明:(1)不同储层类型的组合方式与平面空间分布,对气井产能有较大影响;(2)近井区、过渡带、远井区储层类型分别为裂缝-孔洞型、孔洞型、孔隙型储层(简称为“缝-洞-孔”)时气井生产效果最好,在孔洞型、孔隙型、裂缝-孔洞型储层(简称为“洞-孔-缝”)组合下气井生产效果次之,而在孔隙型、裂缝-孔洞型、孔洞型储层(简称为“孔-缝-洞”)组合下气井产量较低,稳产期较长。研究成果认识与GM区块灯四段气藏多口气井的生产实际情况相符,可为震旦系灯四段气藏和同类气藏(强非均质碳酸盐岩气藏)的井位部署、生产动态调整提供重要的理论依据。

Several reservoirs,including Sinian,Cambrian and Permian,have been explored in deep marine carbonates,Anyue gasfield,Si-chuan Basin.And they feature buried depth ranging from 4,600 m to 5,200 m and strong heterogeneity.Among which,the intra-platform gas reservoirs in the fourth member of the Sinian Dengying Formation(simply as Dengying 4 Member)are a bit thin and multiple superimposi-tion in the vertical while generally exhibit low porosity and permeability.And some of them are improved in their quality owing to natural fractures or dissolution pores and vugs induced from karstification.The reservoirs are divided into three types of fractured–vuggy,vuggy,and porous reservoirs based on pore-vug-fracture combination and its genesis.Given the difference in pore-throat structure and fracture-vug extension scale,they show exclusive seepage characteristics.Thus,numerical simulation on well productivity was conducted under various reservoir combination.Results show that(i)the combination and reservoir planar or spatial distribution exert a great impact on the pro-ductivity;and(ii)near or far from the wellbore and in the transitional zone,the best productivity is achieved under the first combination of fractured–vuggy+vuggy+porous reservoirs(fractured-vuggy-porous reservoirs),followed by the second combination of vuggy+porous+fractured–vuggy reservoirs(vuggy-porous-fractured reservoirs),and the third combination of porous+fractured vuggy+vuggy reservoirs(porous-fractured-vuggy reservoirs)still with smaller productivity and longer stable production period.Consistent with real practice in nu-merous wells targeted Dengying 4 Member,GM block,these results provide important theoretical basis for well deployment and production performance adjustment in such member or similar carbonate gas reservoirs with strong heterogeneity.