A new type of cementation flushing fluid for efficiently removing wellbore filter cake

For effectively removing the water-based drilling fluid filter cake and improving interfacial cementing strength and cementing quality, a new type of cementation flushing fluid (WD-C) was developed based on the strong flushing principle of water soluble fiber and the oxygenolysis principle of filter cake. It is composed of 0.5% WF-H fiber, 2.2% WF-O oxidant, 0.35% FeSO4, 1.8% KCl, 3.0% swollen powder perlite and water with its density of 1.03 g/cm3. This cementation flushing fluid was systematically tested and evaluated in terms of its washing efficiency on the filter cake of water-based drilling fluid and its capacity to improve the bonding strength of cementation interface. In addition, an analysis was performed of its effect on the physical-chemical characteristics and the micro-structures of interfacial cements by means of infrared spectrum (IR), scanning electron microscope (SEM) and energy dispersive X-ray detector (EDS). It is shown that the new cementation flushing fluid presents excellent washing effect on water-based drilling fluid filter cake (with washing time within 10 min). The cement particles at the cemented interface can be hydrated normally, and hydrated calcium silicate gel, Ca(OH)2 and rod-shaped ettringite (AFt) crystal are generated and interwoven with each other. In this way, dense network structures are formed, so the bonding strength of the second cementing interface rises significantly, and then cementing quality is improved. Based on the research results, one more technology is set up for removing the water-based drilling fluid filter cake efficiently and improving the bonding strength of the second cementing interface.