Clay Free Invert Emulsion Drilling Fluid System- An Innovative Rheology Modifier Which Provides Flat Rheology for Deep Water Drilling and Viscosifier for Clay Free System

Abstract

Exploration and Production Operators prefer a non-damaging non-aqueous fluid (NAF) for drilling Reservoir. One of the requirements of non-damaging system is a clay free system and it should perform as good as any NAF Fluid. For drilling in deep water environment, it is necessary to have flat rheology of NAF over a wide range of temperatures. An innovative polymeric rheology modifier was used to develop Clay Free Invert Drilling Fluid (CFIDF) which provides dual function to achieve a clay free system as well as flat rheology when measured over a wide range of temperatures from 40 to 150 °F. The flat rheology is required in offshore deep water drilling due to varying temperature profile from 4 °C at the bottom of sea to as high as 100 °C or even higher at bottom of hole. Lower temperatures increase the rheology leading to higher ECD and at higher temperatures the rheology is lowered leading to hole cleaning issues. Flat rheology profile minimizes or eliminates such adverse effects on ECD or hole cleaning activity. The newly developed clay free system utilizes a single rheology modifier component to provide dual functions of providing true clay free system and offers flat rheological profile without sacrificing the vital mud parameters such as emulsion stability, fluid loss control and rheology. In addition, the system uses a new rheology modifier that provides a temperature-independent rheology profile for hole cleaning, barite suspension, ECD management. The system can be formulated for deep-water applications with mud weights up to 18.0 lb/gal and bottom hole temperatures up to 350°F. Recent successful field trials as a clay free system for drilling reservoir indicated that the new system is easy to maintain and provides good fluid performance in terms of drilling rate, ECD management, lost circulation control and hole cleaning. The product provides an excellent rheological profile and was used in the field at a low dosage of 1 ppb. Even at this low dosage LSRV was above 10 in 8 ½″ Hole with yield point of greater than 15 lbs/100 sq.ft. When the system was contaminated with a severe saltwater flow, there were no fluid-related problems before the synthetic/water ratio was restored. The new fluid system exhibits flat rheology profiles and non-progressive gel structures. The system showed excellent hole cleaning with excellent thixotropic properties. This resulted in a noticeable reduction of lost circulation potential in lost circulation prone areas due to manageable ECD. An innovative rheology modifier which provides clay free system and offering flat rheology profile has been developed and successfully used in field. The rheology modifier can minimize or totally eliminate the organophilic clay to improve the quality of non-damaging reservoir drilling fluid.