低渗透储层的径向电阻率特征及含油性——以鄂尔多斯盆地洛河油田延长组长61为例

鄂尔多斯盆地中部洛河油田长61低渗透油层由于含油饱和度变化大、油层非均质强,再加淡水钻井液侵入,造成油层电阻率径向分布不均且变化大。通过双感应-八侧向测井与阵列感应测井响应特征对比分析,认为水层的径向电阻率均为增阻侵入,油层、油水同层的径向电阻率普遍具有减阻侵入、低阻环带、高阻环带特征或相关趋势。其中,减阻侵入有助于识别高含油饱和度、高电阻率油层和油水同层,低阻环带和高阻环带有助于识别低电阻率油水同层。另外,部分油水同层的双感应-八侧向测井径向电阻率组合具有“增阻侵入”且深感应电阻率低的特征,推测可能是受双感应-八侧向测井探测范围限制,为低阻环带靠近井眼附近遭受淡水钻井液侵入影响的结果,深感应测井反映的是侵入带电阻率而不是油水同层的电阻率,容易被误解释为水层。因此,对于双感应-八侧向测井中具有“增阻侵入”特征且深感应电阻低值的储层,其流体性质有水层、油水同层这两种可能性,需要结合深探测测井资料或油藏地质特征进一步分析,以提高油层、水层的识别率。

Radial resistivity characteristics and oil-bearing properties of low-permeability reservoirs: A case study of the Chang 6-1 Formation in the Luohe oilfield, Ordos Basin

The low-permeability Chang 6-1 reservoir in the Luohe oilfield of central Ordos Basin varies greatly in oil saturation and shows strong heterogeneity. In addition, the invasion of freshwater drilling fluid has also resulted in the uneven radial distribution and great variations of reservoir resistivity. This work performed comparative analysis of dual induction - laterolog 8 and array induction logging on the Chang 6-1 formation. Results indicate that the radial resistivity of water layers is increased resistivity invasion, and the radial resistivity of oil layers and oil-water layers generally shows related trends of decreased resistivity invasion, low resistivity annulus and high resistivity annulus. The decreased resistivity invasion helps to identify the oil layers and oil-water layers of the high oil-saturation and high resistivity, while the low-resistivity annulus and high-resistivity annulus help to identify the oil-water layers of the low resistivity. The radial resistivity combination of dual induction - laterolog 8 in some oil-water layers displays increased resistivity invasion and low deep induction resistivity. It is speculated that it may be limited by the detection range of dual induction - laterolog 8, and is the result of freshwater drilling fluid invasion near the wellbore in low-resistivity annulus. The deep induction resistivity reflects invasion zone, rather than the oil-water layer, which is easily misinterpreted as a water layer. Therefore, the fluid properties in reservoirs with "increased resistivity invasion" characteristics and low deep induction resistivity in dual induction - laterolog 8 may be indicative of water layer or oil-water layer. It is necessary to combine deep detection logging data or reservoir geological characteristics to further analyze and improve the recognition rate of oil and water layers.