Abstract:

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

Key words: water injection, calcium carbonate scale, electron probe, reservoir damage, compatibility