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For many years, barite has been the standard weighting agent in the drilling fluid industry. Its high specific gravity has helped produce mud weights in excess of 19 lb/gal. Its hardness has rendered it easily millable to a particle size that reduces settling and minimizes losses on shaker screens and its adequate inertness has enabled it to be used in a wide range of drilling fluids containing different chemical components. Recently, however, dwindling supplies and increased consumption of premium barite have led to significant price increases across the world and a reduction in specific gravity in most commercial grades. This has led to renewed interest in alternative weight materials.Ilmenite and hematite are two minerals that have been used sporadically in the field. Compared to barite, their higher density impacts both the rheology of the fluids and the settling rate of the weight material. A known issue with these materials is their relatively high hardness, which can give rise to abrasion/erosion in the tubular and surface equipment. Another effect that has not been addressed sufficiently is the magnetic characteristic of these iron oxide-containing minerals which has the potential to affect the operation of direction drilling and some other downhole tools.There have been many studies on the use of ilmenite and hematite as weight agents for drilling fluids. These have dealt with the above issues individually or in a scattered manner. In this paper, we report the results of a comprehensive laboratory study on the application of ilmenite and hematite as weight materials for both water-and oil-based drilling fluids. The study includes the effects of different size grades of the materials on rheology and fluid loss, as well as dynamic and static sag.The paper will present relative abrasiveness of the materials compared to barite as measured by two different methods, and recommend size grades that can minimize the abrasion effects. The paper will also report the results of magnetic property measurements which impact operation of several downhole tools, and compares these with that of barite and several other minerals. To complete the comparative testing of these minerals, the results of heavy metal analysis will also be reported for each test mineral.

In Europe where environmental regulations prohibit the use of oil-based mud, high-temperature wells are drilled with HPHT water-based fluids. Chrome-lignosulfonates are a common component in high-temperature water-based fluids, acting as effective dispersants and conferring excellent fluid-loss control and rheological properties. However, tightening of regulations signals the emergence of restrictions on the use of chrome-based products in water-based fluids. Elsewhere in land operations where currently oil-based fluids are used for high-temperature applications, a move towards HPHT water-based fluids, and ultimately to chromefree fluid systems is thought to be inevitable. Thus, alternative chrome-free products are desired that will perform at least as well as the current products in high-temperature, high-density water-based fluid systems.Fluid-loss control in high-temperature environments can become problematic due to the degradation of many polymers at high temperature. A main challenge is to use a high-temperature synthetic polymer that can control fluid loss without a significant impact on rheology. High-temperature gelling is another problem that may confront high-density fluid systems and lead to significant problems during the drilling operation. This must be prevented by using effective, temperature-stable dispersants.This paper describes the development of a new chrome-free, high-density HPHT water-based fluid system. The new fluid uses a combination of clay and synthetic polymers to provide excellent fluid-loss control and to generate thermally stable rheology. The paper presents the results of extensive testing to show that the use of highly efficient dispersants prevents high-temperature gelling and improves fluid resistance to drill solids contamination. The authors will also present results from an initial field testing of the fluid system. IntroductionEnvironmental considerations have led to increasing interest in the use of water-based drilling fluids (WBM) in applications where oil-based fluids have previously been preferred. In Europe, for example, where environmental regulations prohibit the use of oilbased mud, high-temperature wells are drilled with HPHT water-based fluids. The least expensive and most widely used waterbased fluids for such applications are dispersed muds made up with bentonite clay. The low-colloid version of such fluids uses small amounts of clay for filtercake quality. To improve the rheological stability and fluid-loss properties of these fluids at elevated temperatures, chromium-containing thinners and fluid-loss additives have been used. These additives, however, are increasingly subject to environmental regulation.The environmental constraints have created the need for a chrome-free drilling fluid additive with cost and performance characteristics similar to those of chromium-based additives. One option has been to prepare lignosulfonate additives complexed with other metal ions, e.g., Fe, Ti and Zr. Park (1988) reported that the mixed titanium/zirconium lignosulfona...

In order to remotely control the drilling process it is necessary to measure several drilling fluid parameters automatically. This will increase objectivity of the measurements as well as make it possible to immediately react to changes. The current paper describes in detail the design for an integrated tool combination and the results of a full size yard test of such a combined set of tools for measuring drilling fluid parameters and formation properties automatically. Some of the automated tools have been tested on rig site operations. Results from these individual tests are also presented.The automatic drilling fluid analysis includes viscosity, fluid loss, electric stability measurements and chemical properties like pH. Full viscosity curves for the drilling fluid are measured using configurations and shear rates similar to those suggested by API procedures. Since gel formation curves and fluid loss properties require some sort of controlled static periods, these measurements are made semi-continuous. However, they are automatic and are measured as frequently as possible.An automatic system is included to measure the particle size distribution, concentration and morphology. Knowledge of these parameters is necessary, especially when drilling in depleted reservoirs where particles are added for increasing the wellbore strength.The produced cuttings volume is measured. An automatic system is adapted that determines, with accuracy comparable to that of visual analysis, whether the particles separated at the shaker screens are drill cuttings or cavings produced by an unstable formation. The mineralogy of the cuttings is analysed automatically using Raman spectroscopy, making it possible to evaluate continuously the different formations being drilled.

Summary To remotely control the drilling process, it is necessary to measure several drilling-fluid parameters automatically. This will increase objectivity of the measurements and make it possible to react to changes in real time. The current paper describes in detail the design for an integrated tool combination and the results of a full-size yard test of such a combined set of tools for measuring drilling-fluid parameters and formation properties automatically. Some of the automated tools have been tested on rigsite operations. Results from these individual tests are also presented. The automatic drilling-fluid analysis includes viscosity, fluid loss, electrical-stability (ES) measurements, and chemical properties such as pH. Full viscosity curves for the drilling fluid are measured using configurations and shear rates similar to those suggested by American Petroleum Institute (API) procedures. Because gel-formation curves and fluid-loss properties require some sort of controlled static periods, these measurements are made semicontinuously. However, they are automatic and can be measured as frequently as desired. An automatic system is included to measure the particle-size distribution (PSD), concentration, and morphology. Knowledge of these parameters is necessary, especially when drilling in depleted reservoirs where particles are added for increasing the wellbore strength. The produced-cuttings volume is measured. An automatic system is adapted that determines, with accuracy comparable to that of visual analysis, whether the particles separated at the shaker screens are drill cuttings or cavings produced by an unstable formation. The mineralogy of the cuttings is analyzed automatically using Raman spectroscopy, making it possible to evaluate continuously the different formations being drilled.