油藏中饱和度-电阻率分布规律研究——深入分析低电阻油层基本成因

A study on saturation-resistivity distribution pattern of reservoirs——An in-depth analysis for the basic origin of low resistivity reservoirs

用毛细管理论与岩电实验理论对各油田大量油藏进行实例统计 ,分析了较好储集层中油藏的饱和度 电阻率分布规律 ,得知其控制因素为油、水密度差、自由水平面之上高度和储集层的孔隙结构。据此深入分析了渤海湾地区中、浅层形成低电阻油层的主要背景条件。近些年该区所复查与勘探的低电阻油层大多属于油、水密度差较小 ( 0 .1～ 0 .15g/cm3 )、幅度较低 ( 10～ 2 0m ,甚至小于 10m )的油藏 ;其含油饱和度较低 ( 5 0 %～ 6 0 % ) ,好砂岩油层电阻率比值 (与相邻水层比较 )为 4～ 6 .3;此时 ,由于钻井液侵入、孔隙结构差、粘土附加导电等因素 ,就会形成低电阻油层 ,在淡水钻井液条件下如果用侧向测井 ,将使油、水层差别更小。这一研究将为低电阻油层的分布预测提供依据。图 2表 3参 10 (欧阳健摘 )

Research is conducted on the distribution law of resistivity-saturation in good quality reservoirs using capillary pressure theory, petropysic data, and a great number of case statistics for various oil fields. The research shows that there are some factors, such as density-difference between oil and water, height above level of free water and pore structure in reservoir, control the distribution law of saturation-resistivity. Based on the research,the major background conditions with more details that may cause low resistivity pay zones in middle and shallow depth in Bohai Bay area were analyzed. The most low resistivity pay zones that have been counterchecked and explored in recent years can be attributed to some special reservoirs, in which the density difference is small (i.e.0.1-0.15g/cm 3), the reservoir height is small (i.e.10-20m), and even it may be smaller than 10m. In these special reservoirs, oil saturation is so low that it can be 50-60%, and resistivity ratio could be 4-6.3(comparing with adjacent water-bearing beds). Under this condition, and combined with other factors like invasion of mud filter and poor pore structure etc, oil-bearing reservoir with low resistivity may be formed. If lateral log is run under the condition of mud based fresh water, the difference between oil-bearing and water-bearing formations will be smaller. Most oil-bearing reservoirs that have been discovered in recent years belong to the special one describeb above. All results in the research will be helpful for detecting low resistivity pay zone.