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Water soluble polymers, such as carboxymethylcellulose, xanthan gum, polyacrylamide and modified polyacrylamides are used as additives in many stages of drilling, production, transport and processing of crude oil. In particular, they are used in enhanced mixtures crude oil for driving and gels for injection profile control recovery. These same gels are also used to control the water and gas production during oil production operations. Other applications are as additives for drilling muds in systems for lost circulation and stimulation treatments during hydraulic fracturing gels. Additionally, there are polymer additives for controlling scale deposition and paraffins and asphaltenes.
A drilling fluid consists of a series of chemical additives, its main function is to facilitate drilling a hole into a reservoir with minimal damage to the drilling tools and rock formation. The fluid is injected through a pipe from the surface and is discharged through the drill bit (the drill bit that is cutting the rock formations). So, this fluid flows from the downhole to the surface. A drilling fluid must be capable of:
·Transport drill cuttings from the hole bottom to the surface.
·Keep the drill bit cool and clean.
·Keep the stability of the hole sections not supported.
·Work just like a carrier element cuts formation (gravel) and stabilizer hole.
·Prevent loss of fluid (oil, gas or water) to the perforated permeable rocks.
·Keep the cutting in suspension and landslides in the annular space when the drilling operation stops.
The polymers play a number of critically important roles in the drilling mud, it is first used as a viscosifier. As mentioned above, aqueous solutions of water-soluble polymers show pseudoplastic behavior. This means that the viscosity decreases with increasing shear rate. This behavior is desirable for polymers used in drilling fluids, as during the drilling operation, the solutions must be sufficiently fluid to facilitate pumping of the mixture, and when the operation stops viscosity must increase for solids kept in suspension.
Moreover, the polymers are also used as flocculants or flocculants of clays as required at a given moment. For both polymers are usually used with 12 anionic charges, but they are low molecular weight polymers in the case of the flocculant, and as flocculants they are used high molecular weight polymers.
Another important application of the polymers is used as drilling mud additives to control fluid loss. In this case, the polymers help form a paste on the walls of the formation during the drilling process. The paste prevents migration of fluid which prevents the fluid loses its properties and formation damaged.
As mentioned above, another important application of the polymers is the injection of aqueous solutions as a method of secondary or tertiary recovery of crude oil in the oil industry. This technique is based on the injection of aqueous solutions under pressure from outside to recover the oil drilling a central bore, as shown in Fig. An oil reservoir is formed by a matrix of porous rock or sand, wherein a mixture of oil, water (brine) and gas is found. When carrying just a drilling wellbore pressures natural provide sufficient to remove 20 to 30% of oil content in the formation strength. One of the most effective techniques for removing the remaining oil is dragging with aqueous solutions of high viscosity. This technique is able to provide 70% extraction of crude oil in the formation. The role of these polymer enhanced oil recovery is to increase the viscosity of the aqueous phase. This increase in viscosity can improve the efficiency of oil recovery processes. Water soluble polymers reduce mobility of the aqueous phase to increase its viscosity and reducing the permeability of the porous rock water.