Unlike conventional oil field drilling fluids, polymers are non-toxic, degradable and cause no serious environmental problems. This paper provides information regarding the microstructural behavior of polymers and presents a detailed description of their physical and chemical properties. It also investigates the performance of polymers with respect to drilling and cementing problems such as hole enlargement, shale stabilization, drilling through difficult formations which may cause ion contamination, drilling at high temperatures and cement bond with the formation.
Through experimental and field studies, this work shows which polymers provide optimum carrying capacity, acceptable fluid loss to the formation, smaller filtration cake and thus, the polymers which can be used to obtain a successful liner or casing cementing with less chance of gas leakage.
Compared to other conventional oil field drilling fluids, polymers are the best materials to be used as drilling fluids because they are non-toxic and degradable materials which do not cause environmental problems.
The existing literature for drilling fluids concentrates on the study of a particular polymer and its laboratory behavior. To the best of our knowledge there is no work done to predict the rheological behavior, to present the physical and chemical properties of the polymers, and to address possible solutions in solving the traditional drilling problems using various polymers as drilling fluids. Furthermore, the existing literature does not address the problem of cementing performance in a hole which is drilled using polymer drilling fluids.
Darley and Gray discussed the use of polymers (starch and polyacrylamide) as filtration control agents or as drilling muds and how the temperature affects the behavior of these polymers. They also provided information regarding guar gum, xanthan and CMC and discussed their behavior as drilling fluids. In a paper presented in 1991, Powell and Parks explained the biopolymers rheological properties based on laboratory studies and they discussed the ability of these polymers to suspend and transport cuttings in horizontal holes.
This work provides guidelines for the selection of the best mixture of different polymers that gives an optimum carrying capacity, low level of fluid loss to the formation, hence thin filter cake, and thus a successful liner or casing cementing with minimal gas leakage from the formation.
There are three types of water soluble polymers; polysaccharides (biopolymers), modified polymers, and synthetic polymers (polyacrylamides). Polysaccharides are formed from the polymerization of saccharide molecules from a process called bacteria] fermentation; their molecules are bonded through glycosidic linkages and they are relatively non-ionic. The modified polymers are products of chemical treatment of other polymers to achieve more solubility, less salt contamination, and resistance against bacterial attack. The synthetic polymers are the ones for which their molecular chains grow polymerization.
The structure of polymers under dynamic conditions can be either viscoelastic or plasticoviscous. Under static conditions, polymers exhibit either thixotropic or time independent non-newtonian behavior.
Polymers can be classified under the low solid system which has solid content less than 10% by weight, a density of less than 9.5 ppg, and are water base structure and hydrocolloid materials.