Completion Fluids for Maximizing Productivity--State of the Art
Authors: Millhone Ralph S. 
Published: December 2007

Summary
This paper focuses on prevention of well completion damage through proper choice of working fluids, pressure balance, and lost circulation material. Field pressure balance, and lost circulation material. Field applications are described, and damage prevention is advocated wherever possible. Extensive references are provided for those seeking greater detail on low-density provided for those seeking greater detail on low-density fluids, clear fluids, and nondamaging lost circulation material.

Introduction
Completion fluids are being considered more widely both for their impact on well productivity and for their efficiency in accomplishing a defined objective in a well. The importance of the growing awareness of this should not be understated, since the ultimate measure of the petroleum industry's success is its ability to maximize petroleum industry's success is its ability to maximize productivity and total recovery economically. productivity and total recovery economically. In the widest sense, any fluid that contacts or enters a productive zone during a well job is a completion productive zone during a well job is a completion fluid. Hence, completion fluids include those used in such well activities as pay zone drilling and/or under- reaming, perforating, gravel packing, chemical treatments, hydraulic fracturing, cleanout, well killing, zone selective operations, and tubing and hardware replacement.
Some often conflicting considerations involved in selecting a completion fluid for a particular job are listed in Table 1. A completion fluid is a compromise--a practical balance between safety, efficiency, cost, and practical balance between safety, efficiency, cost, and minimum adverse impact on productivity. No one fluid system is universally optimal.
The purpose of this paper is to summarize state-of-the- art considerations relating to selection and use of completion fluids, with the objective of maximizing productivity. productivity. Completion Damage
Items listed under Completion Damage in Table 1 are major concerns when a completion fluid is chosen. The significance of completion damage has been documented by many field and research studies in the past decade. The potential reward for avoiding past decade. The potential reward for avoiding completion damage is illustrated in Fig. 1. This example shows a nearly 100-fold productivity loss resulting from completion damage sustained during attempts to remedy in-well mechanical problems. That the problem was a completion problem, rather than a reservoir problem, is shown by the result of a redrill, where use of a nondamaging completion fluid returned the well to its natural decline.
Defining potential completion damage problems and selecting fluids to avoid such problems generally is done through laboratory testing. Fig. 2 shows a typical apparatus capable of simulating flow of several fluids past, into, and/or out of the wellbore/formation interface. The accuracy of results from such testing depends on the use of representative, nondamaged core material. It may be necessary to perform this kind of flow test on location in the field, where there is no question that the fluids are representative of those to be used in subsequent actual well work.

Avoiding Completion Damage
The overriding trend in recent efforts toward improved completion fluid systems and operating procedures is to minimize the potential for foreign solids and adversely reactive liquids being introduced into productive formations. Three basic techniques are used.

Underbalanced Operation
Where safety and job objectives permit use of underbalanced fluid systems, they completely avoid the problem of formation invasion. problem of formation invasion. JPT
P. 47