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SPE Paper: A Practical Route to Reduced Wellbore Instability

SPE Paper: A Practical Route to Reduced Wellbore Instability


Ultra-low Invasion Drilling Fluids: A Practical Route to Reduced Wellbore Instability, Reduced Mud Losses, Wellbore Strengthening and Improved Well Productivity


Reducing the invasion of drilling, completion and workover fluids to as low a level as possible will alleviate many problems of mechanically unstable formations, differential sticking and lost circulation. A properly formulated ultra-low invasion fluid (ULIF) will also reduce formation damage and thereby often increase well productivity. In addition, certain classes of ULIF will provide wellbore strengthening.

This paper describes the technology used to produce a class of ULIF and will review the benefits that limiting fluid and pressure invasion of fluid brings to rock integrity, drilling performance and well productivity. The ULIF additives described are biodegradable, environmentally acceptable and can be used in water based, oil based and synthetic based fluids. They are easy to add to any mud system and the ultra- low invasion properties of the fluids are measured and maintained in the field by using a simple sand bed invasion test. The paper focuses mainly on case histories from several regions of the world where ULIFs have been used. In North, Central and South America alone, over 120 wells have used the ULIF additives in the past 3 years. The products have also been used in India, the Middle East, Europe, Africa and the Far East. Log data are presented that clearly demonstrate the ability of a ULIF to reduce wellbore instability and fluid invasion. Evidence of wellbore strengthening is also presented along with several cases where well productivity has been increased. In addition to showing the enhanced technical performance obtained with ULIFs, we also demonstrate the economic benefits of using these fluids.

The same technology used to formulate Ultra-low Invasion Drilling Fluids can also be used very successfully – sometimes with modification – in completion fluids, workover fluids and cementing operations to reduce or eliminate the same problems.

SPE Paper Number: 101329