伊拉克S油田碳酸盐岩储层特征及裂缝孔隙度计算方法

Characteristics of Carbonate Reservoir and Calculating Method of Fracture Porosity in S Oilfield of Iraq

伊拉克北部S油田位于扎格罗斯盆地,主力油层为侏罗系的海相碳酸盐岩,古近纪时阿拉伯板块与欧亚板块发生碰撞,受到剧烈造山运动的影响,储层裂缝非常发育。通过岩心、薄片观察、测井和测试数据分析,认为该油田储层裂缝既是渗流通道,也是重要的储集空间,总体上可以分为两类:裂缝-孔隙型储集空间和裂缝型储集空间。裂缝孔隙度是该类油藏储量计算的重要参数,针对裂缝孔隙度定量计算的难点,通过岩心观察分析和成像测井解释两种方法计算了该油田主力储层的平均裂缝孔隙度分别是0.15%和0.19%。数据分析表明,储层的裂缝孔隙度与裂缝段采油指数呈正相关,裂缝的发育明显改善了储层的渗流性,是该油田获得高产油气流的关键因素。另外,也发现泥质含量超过40%或者石膏含量超过50%的岩石,裂缝孔隙度几乎为零。

S Oilfield in northern Iraq is located in Zegros Basin,whose major reservoir is Jurassic marine carbonate rocks.During Paleogene period,the Arabian plate collided with the Eurasian plate and the reservoir fractures developed well affected by intense orogenic movement.Based on core analysis,slice observation,well logging and testing data,it is concluded that the fractures in Jurassic reservoirs are not only the primary percolation channel,but also an important reservoir spaces including two types of fracture-pore reservoir space and fractured reservoir space.So fracture porosity becomes the important parameters in reserve calculation of this kind of reservoirs.In view of the difficulty in quantitative calculation of the fracture porosity,average fracture porosity of the major reservoirs in this oil field is 0.15% and 0.19% respectively calculated by core observation analysis and imaging logging interpretation.Data analysis shows that the fracture porosity of the reservoirs is positively correlated with the productivity index of the fracture section,and the development of fractures obviously improves the percolation of the reservoirs,which is the key factor to obtain oil-gas flow with high production in this oil field.In addition,it is also found that the fracture porosity is almost zero when the muddy content is more than 40% or the gypsum content is more than 50%.