No abstract

The usage of sepiolite muds is not common in the drilling industry even though they exhibit better rheological properties under high temperature and high salinity environments than those of rivals due to their unacceptable high filtration losses. Recent studies have revealed that it is possible to obtain low filtrate rates from these muds along with commercial additives under static conditions at harsh temperatures and saline environments. On the other hand, the dynamic fluid loss behaviors of sepiolite muds are not a well known phenomena. There is no published work on the dynamic filtration behavior of these muds. The main goal of this study is to characterize the dynamic filtration behavior of sepiolite muds formulated with commercial additives under elevated temperatures and pressures. In addition, effects of particle size gradation of sepiolite clay on dynamic filtration properties of these muds are investigated. The variation of spurt loss volume, dynamic filtration rate, and cake deposition index properties of sepiolite muds are investigated with a computerized dynamic filtration apparatus. Numerous dynamic filtration loss histories with a test duration of 45 to 60 minutes at temperature conditions ranging from 200 to 400 ı F, a filtration pressure of 100 psi (0.7 MPa), and only one sample with 500 psi (3.45 MPa) have been conducted. Three key parameters, namely, spurt loss volume, dynamic filtration rate, and cake deposition index to characterize the dynamic fluid loss of sepiolite muds were determined experimentally. The experiments have resulted in acceptable dynamic filtration rate and cake deposition index values for the fresh water sepiolite-based mud at high temperatures. The experimental results promise that properly formulated sepiolite muds can be a good choice in geothermal well drilling beside their low cost advantages.

Static filtration of drilling fluids has long been recognized as an important parameter for drilling operations. Since the standard laboratory testing procedures only consider static conditions, the filtration and cake properties under continuous circulation and dynamic borehole conditions are not usually well determined. Therefore, the measurement of dynamic filtration is particularly important in order to mimic actual downhole conditions. An experimental study has been carried out by the ITU/PNGE research group to characterize the dynamic filtration properties of clay based drilling fluids. This study is an impressive attempt to figure out the dynamic filtration phenomena of clay based muds. The experimental results obtained from a dynamic filtration apparatus (Fann Model 90) are reported in this study. Bentonite and sepiolite clays based muds formulated with commercial additives have been investigated throughout the study. Numerous dynamic filtration histories with test duration of 45 to 60 minutes at temperature conditions ranging from 150 to 400 °F, and a differential pressure of 100 psi have been applied to muds. Three key parameters namely spurt loss volume, dynamic filtration rate (DFR), and cake deposition index (CDI) have been determined to characterize the dynamic filtration properties of mud samples. Results have revealed that bentonite based muds have better dynamic filtration properties than those of sepiolite muds at temperatures up to 250 °F. However, they have lost their stability over 250 °F. Furthermore, formulated sepiolite based muds have remarkable dynamic filtration rates and cake depositions above 300 °F. To sum up, the experimental results of this study point out that sepiolite based muds might be a good alternative to drill wells experiencing high temperatures, particularly in deep oil, gas and geothermal wells.

There exists a strong relationship between mud and borehole stabilities. Mud instability is associated with flocculation that is primarily caused by high active solids, high electrolyte concentration, and high temperature. Drilling in hot environments coupled with active or reactive solid contamination results in severe operational problems which get worse with the presence of salt intrusion. Therefore, drilling engineers search for alternate drilling fluids to eliminate and/or minimize instability problems such as stuck pipes, circulation loss, excessive torque and drag, inadequate cuttings transport, and sloughing borehole. Such mud should tolerate for accumulation of high amount of reactive solids and mitigate diffetential pressure sticking to avoid stuck pipe. This study is an experimental work to investigate and remediate the rheological and fluid loss properties of both unweighted and barite-weighted sepiolite muds heavily contaminated with active solid. Sepiolite muds were formulated in a certain mixing order of additives. Bentonite clay with API specifications (OCMA) at a rate of 80-lbm/bbl was used to simulate active solid. Rheological properties of mud samples were tested at varying temperatures ranging from ambient to 400oF along with a sodium chloride content of 260,000-ppm (120-lbm/bbl). The filtration loss properties were determined at 300oF. Methylene blue test was also performed to determine the tolerance of sepiolite mud for reactive solid contamination. Sepiolite mud was also investigated for tendency to cause wall sticking to consider incidence of differential pressure sticking of drill pipe. Bulk Sticking Coefficient (Ksc) of sepiolite based mud was determined as indicator parameters under high pressure (500 psi) and high temperature (up to 400oF). Sepiolite mud samples resulted in appropriate yield point, plastic viscosity, and water loss values. More importantly, Methylene Blue values lower than 13-lb/bbl and appropriate sticking coefficient were the concrete usability indicator of sepiolite muds against heavily reactive-clay contamination. In other words, sepiolite muds might be a good alternative to drill wells experiencing instability problems resulting from active solid contamination and differential sticking.

There exists a strong relationship between mud and borehole stabilities. Mud instability is associated with flocculation that is primarily caused by high active solids, high electrolyte concentration, and high temperature. Drilling in hot environments coupled with active or reactive solid contamination results in severe operational problems which get worse with the presence of salt intrusion. Therefore, drilling engineers search for alternate drilling fluids to eliminate and/or minimize instability problems such as stuck pipes, circulation loss, excessive torque and drag, inadequate cuttings transport, and sloughing borehole. Such mud should tolerate for accumulation of high amount of reactive solids and mitigate diffetential pressure sticking to avoid stuck pipe.This study is an experimental work to investigate and remediate the rheological and fluid loss properties of both unweighted and barite-weighted sepiolite muds heavily contaminated with active solid. Sepiolite muds were formulated in a certain mixing order of additives. Bentonite clay with API specifications (OCMA) at a rate of 80-lbm/bbl was used to simulate active solid. Rheological properties of mud samples were tested at varying temperatures ranging from ambient to 400°F along with a sodium chloride content of 260, 000-ppm (120-lbm/bbl). The filtration loss properties were determined at 300°F. Methylene blue test was also performed to determine the tolerance of sepiolite mud for reactive solid contamination. Sepiolite mud was also investigated for tendency to cause wall sticking to consider incidence of differential pressure sticking of drill pipe. Bulk Sticking Coefficient (K sc ) of sepiolite based mud was determined as indicator parameters under high pressure (500 psi) and high temperature (up to 400°F).Sepiolite mud samples resulted in appropriate yield point, plastic viscosity, and water loss values. More importantly, Methylene Blue values lower than 13-lb/bbl and appropriate sticking coefficient were the concrete usability indicator of sepiolite muds against heavily reactive-clay contamination. In other words, sepiolite muds might be a good alternative to drill wells experiencing instability problems resulting from active solid contamination and differential sticking.