砂泥岩薄互层低阻油层地质成因——以珠江口盆地A油藏M_1油组为例

Geological Genesis of Low Resistivity Formation with Thin Sand-Shale Interlayer——An example from M1 oil measure of A reservoir in Pearl River Mouth basin

珠江口盆地A油藏M1油组为高孔低渗低阻油藏,为了查明造成油层低电阻率的主要原因,从储集层岩石粒度、泥质含量及粘土矿物类型和分布形式、孔隙结构特征、导电矿物含量、砂泥岩薄互层发育状况等方面进行分析,并与高阻层段M2油组进行对比。形成M1油组低电阻率的主要原因是:储集层细颗粒含量高,泥质含量高,细微孔喉体积百分数高,造成储集层束缚水饱和度高,增强了油层的导电性能;粘土矿物以伊蒙混层和高岭石为主,呈薄膜状、絮状、分散状分布,增强了储集层的附加导电能力;砂泥岩薄互层的发育使本身低阻的油层受围岩低电阻率的影响而变得更低。导电矿物和地层水矿化度虽对储集层电阻率降低有一定影响,但不是主要因素。

M1 oil measure of A reservoir in Pearl River Mouth basin is characterized by high porosity, low permeability and low resistivity. In order to examine its main control factor of low resistivity, this paper conducts the analyses of the grain size distribution, shale content, clay mineral type and distributive form, pore structural feature, conductive mineral content, thin sand-shale interlayer development status, with comparison with M2 oil measure of high resistivity. It is concluded that there are three factors for it： the reservoir is of high fine-particle content, high shale content, high percentage of fine pore throat volume, which result in its high irreducible water saturation and enhance its conductive property; its clay mineral is dominated by illite-montmorillonite mixed layer and kaolinite, showing film-like, flocculation-like and dispersion-like distribution, enhancing its additional conductivity; the development of thin sand-shale interlayer allows the low-resistivity formation of its own to become much lower by the effect of surrounding rocks with low resistivity. Also, the conductive minerals and the salinity of formation water have some effects on reducing resistivity of the reservoir, but they are not main factors for it.