Fluid Design to Minimize Invasive Damage In Horizontal Wells
Authors: Bennion D.B. , Thomas F.B. , Bennion D.W. , Bietz R.F. 
Published: March 2010

Abstract
Formation damage is a very reservoir specific process, but extensive studies indicate that generalities can often be drawn with respect to certain types and mechanisms of damage which are more prevalent with various reservoir types. This paper provides a mechanistic discussion of various types of formation damage common to horizontal wells, such as fluid-fluid and rock-fluid incompatibilities, solids invasion, effect of overbalance pressure, aqueous phase trapping, chemical adsorption, wettability alteration, microbiological activity, and fines migration. These phenomena are discussed and how they specifically relate to the following formation types:Clean and dirty homogeneous sands.Clean and dirty laminated sands.Unconsolidated sands.Fractured sands.Homogeneous carbonates.Fractured carbonates.Vugular carbonates.
Recommendations for various fluid types and procedures which have experienced success in certain situations are also presented. Laboratory testing of fluids and representative core samples is highlighted as a potential diagnostic tool to select the optimum fluids for drilling, completion, stimulation and workover treatments. Use of these guidelines can, in many cases, narrow the choice of potential fluids considered for use in a given lithofacies type and increase the efficiency of the optimization process.

Introduction
Horizontal drilling is being utilized in an ever increasing fashion to exploit reservoirs exhibiting thin pay zones, problems with water or gas coning, to obtain greater reservoir exposure and to maximize the productive potential of naturally fractured reservoirs. Reductions in the productivity of these horizontal wells due to improperly or inadequately designed drilling, completion or workover programs is a frequent occurrance. This paper documents common areas for potential reductions in the productivity of horizontal wells completed in oil or gas bearing formations due to invasive formation damage and provides general criteria for the design and selection of fluids and operating programs to minimize potential damage.

Invasive Formation Damage
Formation damage can be described as any phenomenon induced by the drilling, completion or stimulation process or by regular operations resulting in a permanent reduction in the productivity of a producing oil or gas well or the reduction in the injectivity of a water or gas injection well.
Invasive formation damage can occur by the introduction of:Foreign potentially incompatible fluids into the formation.Natural or artificial solids.Extraneous immiscible phases.Physical mechanical damage.
Further information on some of the specific mechanisms of these various types of invasive damage will be elucidated upon later in the paper.

Formation Damage in Horizontal vs. Vertical Wells
A detailed discussion of mechanisms of formation damage in horizontal wells has been presented in the literature(1). Formation damage tends to be more significant in horizontal vs. vertical wells for a number of reasons, some of these being:Longer fluid exposure time to the formation during drilling and greater potential depth of invasion in situations where sustained fluid and solids losses to the formation are apparent.