Chrome-free lignosulfonates are increasingly used in aqueous drilling fluids because of potential environmental concerns associated with the chromium counterparts. A basic design study of a chrome-free lignosulfonate showed three major reaction parameters affecting its performance: type and concentration of complexed metal ion. oxidation level under optimal pH and lignosulfonate raw liquor. A new chrome-free lignosulfonate formulation based on titanium metal ion was developed and its plant scale-up was conducted. Testing of the new titanium-complexed lignosulfonate was found to give improved rheological control vs. other available chrome-free lignosulfonates in various water-based drilling fluid applications.
Introduction
Chromium-based lignosulfonates were introduced to the drilling industry more than 30 years ago. They have been used as water-based mud additives continuously since initial introduction. During early development work with lignosulfonates, King described a drilling-fluid additive formulated with such metal ions as chromium, iron, and aluminum. and spent lignin liquor. The drilling industry has successfully used the chromium-based lignosulfonates as drilling fluid additives in a wide variety of drilling environments and over a broad temperature range.
Use of chromium lignosulfonate in drilling fluids has been discontinued in certain areas because of possible harm to the environment. It is generally accepted throughout the drilling industry that drilling fluid additives containing hexavalent chromium are toxic to the environment. Several papers have been published on the harmful effects of discharging fluids containing chromium or iron/ chromium lignosulfonates into waterways. If chromium-containing drilling fluids are used in a particularly sensitive area, it is necessary to remove the drilled cuttings from the site, dispose of the drilling fluid at a classified disposal site, and treat the holding pits used to contain such fluids. These environmental constraints have created the need for a chromium-free drilling fluid additive with processing-cost/performance characteristics and versatility equivalent to those of chromium lignosulfonates.
Several chromium-free modified lignosulfonate drilling fluid additives have been introduced to the drilling industry in recent years These chromium-free additives are, in many cases, not as effective as chromium lignosulfonate when tested in a wide range of applications. Some or all of the following performance deficiencies were observed when available chromium-free lignosulfonates were tested.
Typical drilling fluids treated with available chromium-free modified lignosulfonates proved less tolerant to solids and more sensitive to high temperatures than similar drilling fluids treated with chromium lignosulfonates. In addition, these chromium-free additives exhibited inferior performance when added to seawater and other inhibited drilling fluids. These fluids also displayed a lack of gel-strength control at high temperature and a sensitivity to pH variati.
A new chromium-free drilling fluid additive has been developed. This additive is a titanium-based lignosulfonate prepared under optimum reaction conditions. The titanium lignosulfonate controls rheological properties of drilling fluids as well as chromium lignosulfonates.
