Polymer-Polyelectrolyte Drilling Fluid Systems
Authors: Browning W.C. , Chesser B.G. 
Published: December 2007

Described here is a new drilling fluid technique in which polyelectrolytes in a nonseptizing aqueous medium are used polyelectrolytes in a nonseptizing aqueous medium are used to obtain borehole stabilization, and in which thixotropic shear-thinning organic polymers are used instead of clays to obtain rheological properties favorable for hole cleaning. Drilling fluids so designed are nondispersing to drilled formation solids and possess maximized penetration-rate rheology.

Introduction
Detailed investigations of the effect of drilling fluids upon penetration rate have demonstrated that it is not solids content or filtration rate per se that controls penetration rate but the kinematic viscosity of the fluid at shear rates comparable with those at the bit nozzles.
Practical experience has repeatedly demonstrated that water, a low-viscosity Newtonian fluid, will not always provide proper hole cleaning. To clean the hole effectively, a satisfactory drilling fluid must be capable of providing controllable and sufficiently high "Marsh Funnel" viscosities and also a water-thin consistency through the bit nozzles. These apparently contradictory conditions can be satisfied by the use of polymeric, organic, shear-thinning materials instead of clay.
Drilling hydraulics is recognized to be a significant factor in efficient drilling. Other problems associated with drilling through troublesome formations must not be ignored, however, by overemphasis on hydraulics.
Increased rate of penetration is known to lower costs while "making hole," but over-all costs will continue to accumulate while not drilling ahead. Although wellbore stabilization has attracted attention for many years, there is at present no common agreement concerning how it may be achieved. There is even disagreement regarding the basic factors of wellbore instability. The laboratory testing of borehole stability has progressed in recent years, but the results remain progressed in recent years, but the results remain incomplete and subject to bias. Published conclusions are frequently contradictory with each other and with operating experience. The only reliable evaluation of wellbore stabilizing techniques is through the actual drilling of a well. If carefully conducted, a well test permits accumulation of meaningful data regarding permits accumulation of meaningful data regarding materials consumption, rate of penetration, mechanical operation, hole enlargement (by caliper log), and other operating characteristics.
This paper presents two things:
a concept of a nonclay drilling fluid system and laboratory and field results of one particular drilling fluid fitting this concept.
The polymer-polyelectrolyte system concept given in this paper embodies the objectives of a modern drilling fluid. This system consists of a nondispersing water medium in which is dissolved an organic polyelectrolyte capable of adsorbing upon exposed clay surfaces to form a coherent film. This condensed adsorption film protects the exposed formation from liquid invasion. In this system no clay additions are necessary to control fluid properties. Rheological control is maintained at high and low shear rates with shear-thinning polymers.
The laboratory and field results given are those obtained with currently available chemicals. It is expected that improved chemicals of less cost, greater heat stability, and improved rheological performance will be developed.
JPT
P. 1255