1. Determine the amount to be added
- Based on drilling conditions : The amount to be added mainly depends on the type of drilling fluid, formation characteristics, and specific requirements of the drilling operation. For example, when drilling in a formation prone to collapse, the amount of polyanionic cellulose (PAC) added may be relatively high in order to better stabilize the wellbore and control the filtration loss. Generally speaking, the amount of PAC added to the drilling fluid is usually between 0.2% and 1.5% (mass fraction).
- Experimental determination : Before actual application, it is best to determine the optimal amount to be added through laboratory experiments. You can simulate downhole temperature, pressure, and formation conditions, prepare drilling fluid samples with different PAC contents, and then test these samples for rheological properties (such as viscosity, shear force, etc.), filtration loss performance, and other indicators. According to the test results, select the minimum PAC addition amount that meets the drilling fluid performance requirements, which can both ensure the performance of the drilling fluid and reduce costs.
2. Select the adding method
- Dry powder adding :
- Prehydration treatment : If dry powder adding method is adopted, it is best to prehydrate PAC first. Because when PAC dry powder is directly added to drilling fluid, it is easy to form "fish eyes" (dry powder particles that are not fully dispersed), which affects its performance. During prehydration, slowly add PAC dry powder to a certain amount of water and stir it at the same time. The water temperature is generally controlled at about 40-50℃, and the stirring time is about 1-2 hours, until PAC is completely dissolved to form a uniform glue.
- Slowly add drilling fluid : Slowly add the prehydrated PAC glue to the stirring drilling fluid system. The stirring speed should be moderate, generally controlled at about 300-500 rpm, so as to ensure that the PAC glue is fully dispersed and uniform in the drilling fluid, and avoid excessive local concentration affecting the performance of the drilling fluid.
- Adding glue :
- Preparing glue concentration : If adding in glue form, first prepare PAC glue of appropriate concentration. PAC is usually prepared into 5% - 10% (mass fraction) glue. When preparing, slowly add PAC into water under stirring conditions, and continue stirring until it is completely dissolved. It can be heated appropriately during the dissolution process to accelerate the dissolution, but the temperature should not be too high to avoid affecting the performance of PAC.
- Continuous and uniform addition : The prepared PAC glue is continuously and evenly added to the drilling fluid circulation system through a special dosing device. The addition speed should be determined according to the circulation speed of the drilling fluid and the required final concentration of PAC. Generally, it is necessary to ensure that PAC can be evenly distributed in the entire drilling fluid system within one cycle.
3. Consider compatibility
- Interaction with other additives : When adding PAC, consider its compatibility with other additives in the drilling fluid (such as bentonite, barite, fluid loss reducer, viscosity enhancer, etc.). Some additives may react chemically with PAC, affecting its performance. For example, PAC and certain cationic additives may react with flocculation, resulting in deterioration of drilling fluid performance. Therefore, before adding PAC, it is necessary to understand other additives in the drilling fluid system and verify their compatibility through experiments.
- Adjust drilling fluid formula : If it is found that PAC has compatibility problems with other additives, the drilling fluid formula can be adjusted appropriately. For example, change the type or order of addition of other additives, or adjust the amount and method of addition of PAC to ensure stable and good performance of the entire drilling fluid system.
4. Monitoring and adjustment
- Performance monitoring : After adding PAC, the performance of the drilling fluid should be monitored in real time. The main monitoring indicators include viscosity, shear force, filtration loss, pH value, etc. Specialized drilling fluid performance testing instruments can be used, such as six-speed rotational viscometer, high temperature and high pressure filtration meter, etc. According to the monitoring results, changes in drilling fluid performance can be discovered in time.
- Dynamic adjustment : If it is found that the drilling fluid performance does not meet the requirements, such as viscosity decreases or filtration loss increases, the amount of PAC added should be adjusted in time or other remedial measures should be taken. For example, if the filtration loss increases, the amount of PAC added can be appropriately increased.
