A New Approach to High Temperature Drilling Fields

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract The clay mineral sepiolite has been under investigation since 1972 by our laboratories for possible use in drilling fluids. This paper reviews the work done on this clay mineral in an effort to obtain a drilling fluid capable of withstanding temperatures in the ultra high range. This includes a study on the rheology of sepiolite slurries that have been subjected to temperatures up to 800 deg. F. X-ray diffraction techniques and scanning electron microscope studies were used to examine the crystalline structure of the sepiolite before and after exposure to these high temperatures. There appears to be some changes in the sepiolite after being subjected to temperatures up to 800 deg. F. However, the basic structure seems to be stable. Data is given showing that slurries prepared from sepiolite and other additives have favorable rheological and fluid loss properties over wide temperature ranges. properties over wide temperature ranges Introduction Sepiolites belong to a group of magnesian silicates, with a fibrous texture, whose idealized formula can be written Si12Mg8O32nH2O. This mineral is believed to have microporosity, giving it a unique place in the clay mineral family because of its structural characteristics and physics-chemical properties. Sepiolites derive much of their commercial value from their molecular sized channels and grooves. The channels are lost when the crystals fold, which occurs when the temperatures are elevated and water is driven out of a dry sample of sepiolite. The conditions necessary for folding and the stages and mechanism of this change are only partially understood. Our studies show that when a sepiolite slurry is subjected to elevated temperatures, the channels take on water and swelling occurs. In our studies of slurries containing sepiolite, it was observed that the rheological properties of the slurries showed a slight increase in viscosity when measured at elevated temperatures and pressures. Due to this apparent temperature stability, formulations containing sepiolite were prepared and tested at these extreme conditions. Parameters that are important for good drilling fluid performance were measured and recorded. CHARACTERISTICS OF SEPIOLITE AS A CLAY MINERAL Reports are available on various studies conducted on sepiolite and related clay mineral. Sepiolite deposits and sepiolite/attapulgite deposits have been used in Europe for saltwater clays in drilling muds in lieu of attapulgite normally used in the United States. Oil Companies Materials Association specifications for salt-water drilling clays include sepiolite. At the present time, the API does not recognize sepiolite as a saltwater clay for drilling fluids.