As a kind of treating agent to improve the performance of drilling and completion fluids, Sodium carboxymethyl Cellulose has a main role in reducing fluid loss and increasing viscosity. Sodium carboxymethyl Cellulose is easily dispersed in all water-base drilling fluids and applicable from fresh water to saturated salt water drilling fluids. In low-solid and solid-free drilling fluids, it can strikingly reduce the filtration loss and thin the cake thickness, and has a strong inhibitory effect on the shale hydration. Currently there are mainly two kinds of methods for the production of Sodium carboxymethyl Cellulose, dough process and slurry process. The carboxymethyl cellulose prepared by a certain solvent system, liquor ratio, or certain process conditions, applied in oil drilling, also known as polyanionic cellulose (Polyanionic cellulose) abroad, is actually the Sodium carboxymethyl Cellulose of better performance, but compared with ordinary Sodium carboxymethyl Cellulose, can achieve the maximum economic benefits with the minimum amount.

 

Like ordinary Sodium carboxymethyl Cellulose, in the preparation process of Polyanionic cellulose, the main chemical reactions are divided into two steps: cellulose reacts with alkali aqueous solution to form alkali cellulose; the etherification reaction of alkali cellulose and sodium monochloro acetate (or monochloro acetic acid). The chemical reaction equation is:

 

[C6H7O2(OH)3]n＋n ClCH2COOH＋2n NaOH→[C6H7O2(OH)2OCH2COONa]n＋n NaCl＋2n H2O

 

Solvent process is used in the preparation of Polyanionic cellulose. Solvent process is also called organic solvent process, a process method for alkalization and etherification reactions under the condition of the organic solvent (diluent) as the medium. According to the amount of reaction diluent, it can be divided into dough process and slurry process. As long as process control is appropriate, Polyanionic cellulose of high performance can be obtained by both processes.

The amount of organic diluent used in the dough process is 1-4 times the amount of cellulose (V/W), usually with the use of ethanol as the solvent, while the amount of organic diluent used in the slurry process is 9-30 times the amount of cellulose, usually with the use of isopropanol/ethanol or isopropanol as the solvent. The reactive solids are in the state of porridge and suspension in the system, so also known as suspension process or slurry process. In the solvent process the organic solvent is used as reaction medium. The heat and mass transfer is rapid and uniform. The main reaction accelerates, while the side reaction reduces. The utilization of the etherifying agent (ether efficiency) can be improved by 10%-20% than aqueous medium process, and the reaction stability and uniformity are improved, so that the substitution degree, substitution uniformity and use performance of products are greatly improved, which is the direction of industrial development of cellulose ethers.

 

From experimental data, the following conclusions can be drawn:

In the experiment at normal temperature, the Polyanionic cellulose high viscosity products prepared by dough process and slurry process have the same apparent viscosity, and the filtration loss is lower by slurry process than by dough process, indicating that the Polyanionic cellulose high viscosity products produced by slurry process is superior to those by dough process in reducing fluid loss at normal temperature.

In the experiment at high temperature, the Polyanionic cellulose high viscosity products prepared by slurry process are higher in the apparent viscosity and lower in the filtration loss than by dough process, indicating that after hot rolling at 120℃, the Polyanionic cellulose high viscosity products produced by slurry process are superior in the performance to those by dough process, meanwhile indicating that the Polyanionic cellulose high viscosity products produced by slurry process are more uniformly substituted and can better withstand the test of high temperature.

The reason for the differences in the performance is analyzed and is that in the production by slurry process the isopropanol or isopropanol/ethanol system of long liquor ration is used. The heat and mass transfer is uniform. Carboxymethyl are uniformly substituted, and can have better water retention capacity under the same conditions, which is, therefore, shown in that resistance of products to temperature (acid, temperature, salt) gets improved.

 

2.

In the experiment at normal temperature, the Polyanionic cellulose low viscosity products prepared by dough process and slurry process have the same apparent viscosity, and the filtration loss is lower by slurry process than by dough process, indicating that the Polyanionic cellulose low viscosity products produced by slurry process is superior to those by dough process in reducing fluid loss at normal temperature.

In the experiment at high temperature, the Polyanionic cellulose low viscosity products prepared by slurry process are higher in the apparent viscosity and lower in the filtration loss than by dough process, indicating that after hot rolling at 120℃, the Polyanionic cellulose low viscosity products produced by slurry process are superior in the performance to those by dough process, meanwhile indicating that the Polyanionic cellulose low viscosity products produced by slurry process are more uniformly substituted and can better withstand the test of high temperature.

 

Conclusions:

1). The industrial dough process, due to the limited amount of solvent (diluent), cannot achieve full and complete infiltration and dispersion of cellulose, and the uneven reaction phenomenon tends to exist, so that the product is lack of substitution uniformity and not easy to meet the application requirements after high-temperature thermal rolling.

2). The industrial slurry process is that cellulose is in full contact with alkali solution or etherifying agent by means of stirrer under the condition of long liquor ratio, makes uniform mass and heat transfer, and achieves uniform alkalization and etherification reactions, so the product is better in the substitution uniformity and relatively easy to meet the application requirements after high-temperature thermal rolling.