ABSTRACT
With new wells often costing in excess of $1,000,000, productivity must be maximized to ensure commercial success. To achieve high productivity, so essential to the profitable development of new reserves, the use of non-damaging fluids for drilling-in, completion and/or well-killing operations is mandatory. Formulation of a non-damaging fluid compatible with hostile reservoir environment is complicated by hot, high-pressure formations that require fluids having densities greater than that of water.
Clear, solids-free fluids, thought to be the solution, are widely used. These fluids often contain more than 20% dissolved salts, consequently, their chemistry is complex and proper use requires much understanding and experience. There is mounting evidence from field applications that clear completion fluids do not provide adequate protection against formation damage due to salts precipitating in the reservoir. Equally troublesome is the tendency of the clear fluids to deposit fine particulates, mill scale and etc., on the face of the formation thus causing hard-to-remove damage, especially in the case of gravel-pack completions.
Another popular class of high-density fluids is formulated using acid-soluble particulates as weighting agents. In the most advanced fluids of this class, the particles are suspended in water or brine by non-damaging polymers. Use of these fluids avoid all of the residual problems associated with clear, high-density fluids. When extreme situations warrant, particulate-weighting can be complemented with dissolved salts to maximize protection against damage. Any temporary productivity loss due to the particulates in these fluids is restricted to the surface of the wellbore and can be removed by simply washing the formation face with hydrochloric acid.
