岐口18-1油田沙河街组储层结垢机理及对注水开发影响研究

Study on scaling mechanism and its effect on water flooding in Shahejie formation of QK 18-1 Oilfield

岐口18-1油田位于渤海西部,历经10余年的注水开发,现阶段油田注水困难。2013年对新钻开发井P13井密闭取心,该井岩心代表油田长期注水开发后储层孔隙结构的变化、无机垢堵塞等信息。通过对比早期探井和后期开发井储层中填隙物特征,结合低场核磁共振仪、电子探针、环境电子显微镜、阴极发光、岩石铸体薄片等多种手段研究储层中无机垢,明确了储层中垢晶的形成机理。研究表明,储层中早期的CaCO_3胶结物呈连晶或斑状分布,为成岩阶段的产物;P13井岩心中含大量CaCO_3垢,垢晶呈菱面体,粒径5~30μm,自形程度好,主要分布于骨架颗粒表面及喉道处,且垢晶中Mg、Fe元素含量较高,是注水开发后结垢的产物。储层平均水敏损害率44.5%,平均速敏损害率139.5%,部分垢晶与水化膨胀后的黏土矿物,可运移的地层颗粒,注入水中的悬浮物包裹形成复合包裹体,堆积在孔隙空间内损害储层。

QK 18-1 Oilfield is located in the western Bohai sea. After 10 years of water flooding, the water injection now is difficult. In 2013, the sealed coring was conducted on the well P13. The core represented large amounts of the information after the long term of the water flooding, including the pore structure changes, the inorganic scale plugging, etc. By comparing the interstitial materials in the reservoir of the exploratory wells in the early stage and the exploitation wells in the late stage, we used many methods, such as the low field NMR, the electron microprobe, the environmental electron microscope, the cathodoluminescence and the rock cast sections, to study the inorganic scale in the reservoir and determine the formation mechanism of the scaling crystal in the reservoir. The results showed that the CaCO3 cements in the early stage of the reservoir presented as the crystal or the porphyritic distribution were the products of the diagenetic stage. The well P13 contained a large number of rhombohedral CaCO3 scales with the grain diameter of 5 - 30 μm and great euhedral degree of the scale. And the scale mainly distributed around the surface and the throat of the skeleton particles with high content of Mg and Fe formed during the water flooding. The average reservoir water damage rate was 44.5 % and the average velocity sensitive damage rate was 139.5 %. The clay minerals generated by swelling of part of the scale with water, the mobile formation particles and the suspension matter in water wrapped together to form a composite inclusion, accumulating in the pore space to damage the reservoir.