Anti-accretion additives for drilling fluids

Abstract

Additives for drilling fluids, in particular for water-based drilling fluids are described which when added to the fluid at levels of up to 10% weight by volume reduces the accretion and bit-balling tendencies of shale cuttings exposed to said fluids. The additives are based on phosphonate chemistry, and are of the general class (I), wherein R, R′ and R″ are radicals exclusively containing H atoms or combinations of H, C, O or P atoms up to a maximum of 100 atoms.

Description

This invention relates to anti-accretion additives for drilling muds. BACKGROUND OF THE INVENTION Bit-balling and cuttings accretion are problems encountered when drilling shales, particularly with water-based muds. Shale cuttings can adhere to each other and to the bottom hole assembly and cutting surfaces of the bit. Gradually a large plastic mass builds up which can block mud circulation and reduce rates of penetration. There is a “danger zone” of clay plasticity for balling and accretion, related to the water content of the clay or shale, which can be defined in terms of the Atterberg limits of soil mechanics. In the dry zone the clay has too little water to stick together and it is a friable and brittle solid. In the wet zone the material is essentially liquid like with very little inherent strength and can be washed away.—Intermediate to these zones, i.e., in the danger zone, the shale is a sticky plastic solid with greatly increased agglomeration properties and inherent str...

AI Technical Summary

Benefits of technology

The invention is an additive for drilling mud. The additive reduces the accretion and bit-balling tendencies of cuttings exposed to said muds. The additives are based on phosphonate chemistry, and are preferably of the general class:

Problems solved by technology

Bit-balling and cuttings accretion are problems encountered when drilling shales, particularly with water-based muds.

In the dry zone the clay has too little water to stick together and it is a friable and brittle solid.

However recent advances in drilling fluid technology have developed highly inhibitive muds which appear to reduce the hydration of shale and in doing so maintain the cuttings in the danger or plastic zone contributing to increased accretion and bit-balling.

Field experiences with glycol, phosphate and silicate muds in particular have shown accretion problems.

Images