柴达木盆地狮子沟油田N1油藏低阻油层形成机理

低电阻率油层与邻近水层或泥岩层的电阻率值极为接近，给油、水层识别造成困难，因此，低电阻率油层的评价是当前测井解释方面普遍关注的难题。狮子沟N1油藏在开发过程中发现部分低阻油层，这些油层电阻率指数小于3，电阻率只有2.2 Ω·m（中40井Ⅱ-37），而水层最高的电阻率是4.9 Ω·m（中11井Ⅱ-11），平均电阻率为2.74 Ω·m；由于油、水层电阻率十分接近，这类油层很难识别。通过目前的试采资料，分析了引起该油田低阻的可能原因，主要有：①储层岩性细；②泥质含量高，储层岩石阳离子交换量大；③油藏幅度低，油水密度差小，含油饱和度低；④地层水矿化度高；⑤受断层的影响，储层孔隙结构复杂。按常规的解释标准和解释图版对低阻层进行解释，无法区分油层和水层。建议对该油藏进行深入研究和试油，开展高压物性实验，建立起新的解释模型，使该油藏能够得到高效开发。

Formation Mechanisms of Low Resistivity Pay Zone in Shizigou N1 Reservoir, Chaidamu Basin

For low resistivity pay zones and the adjacent water sand or mud sand show little difference in resistivity from each other, it is difficult to distinguish the oil and the water and the evaluation of low resistivity pay zones has drawn great attention in well log interpretation. Some low resisitivity pay layers were discovered in the Shizigou N1 reservoir, the resisitivity indexes of those layers are less than 3 and the resisitivity is only 2.2 Ω·m (Middle 40 Well Ⅱ-37), while the highest resisitivity of the water sand is 4.9 Ω·m（Middle 11 Well Ⅱ-11）and the average value is 2.74Ω·m. For the approximate values, it is difficult to distinguish them. By analyzing the present producing test data, the main reasons for the low resistivity can be summarized as: (1) fine reservoir lithology; (2) high shale content, which results in large exchange of positive ions in reservoir beds; (3) lower reservoir amplitude, small difference in the density of oil and water, low oil saturation; (4) higher salinity of formation water; (5) complicate pore structures due to faults. It is deficient to study on the zones only by the routine interpretation criterions and charts. So further study should be carried out, new interpretation model should be constructed to improve the development of Shizigou N1 reservoir, by means of well test and PVT test. -