This paper was presented by an SPE Program Committee following review of Information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the or SPE, their officers, or members. Papers presented at SPE meetings are subject to publication review by editorial Committees of the IADC and SPE. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Write Publications Manager, SPE, P.O. Box 833838, Richardson, TX 75083-3836 U.S.A. Telex, 730989 SPEDAL. Abstract It is known that the plastic Bingham model is inadequate to represent some types of drilling fluids, such as low solids and emulsions, especially at medium and low shear rates. Previous experiments on carrying capacity concluded that the average annular velocity and rheological properties affect the fluid transport more significantly than other parameters. Many of these experiments refer to the yield point of the Bingham model, calculated at high shear rates as the most important parameter. This experiment studies how the initial gel strength and plastic yield point affect the carrying capacity of the drilling fluids employing the transport ratio concept. For this purpose the terminal settling velocity of the drilled solids through quiescent fluids was experimentally determined. The results showed a better correlation with the initial gel strength than with the yield point. Also, the analysis of the results demonstrated that a gel strength of about 1.92 Pa (4.0 lbf/100 ft2) is necessary and substantial to obtain a transport ratio higher than 0.50 when the annular velocity is in the range of 0.41 m/s (80 ft/min) to 0.66 m/s (130 ft/min), using low solids and polymer drilling fluids. For any type of water based drilling fluids a gel strength in the range of 3.35 Pa (7 lbf/100 ft2) to 4.79 Pa (9.0 lbf/100 ft2) is sufficient to remove the cuttings at more than 0.50 of transport ratio, even when the annular velocity is about 0.25 m/s *50 ft/min). Introduction The transport of drilled solids from the bottom hole to the surface, throughout the annulus, is one of the main objectives of the drilling fluids. The terms removal velocity and transport ratio are often used to estimate the ability of a drilling fluid to transport drilled solids in a vertical well. The removal velocity is a mean value of the relative cuttings velocity which is equal to the difference between the average annular fluid velocity and the ave rage slip velocity of the cuttings. (1) Vr = Va − Vs The average annulus velocity is defined as a function of the flow rate and the dimensions of the annulus, while the slip velocity is defined as the average velocity at which the particles tend to settle in a fluid. This velocity depends on the size of the particle, its geometry, its density, and properties of the fluid, mainly rheological and density. The transport ratio is defined as follows: (2) Va Vr = Rt = = 1 − ( Vs Va ) The analysis of the equation (2) shows that the transport ratio increases when the slip velocity decreases or the annular velocity increases. If the slip velocity is equal to zero, then the transport ratio will be transported with the same annular velocity. Conversely, if the slip velocity is high the transport ratio will be low. In this case, note that the concentration of the solid in the annulus will increases.

This study describes experiments and techniques relative to the control of solids and fluids used for deep well drilling, in the Marajo Basin, in the Amazon area, in Brazil, where the well bottom temperatures reach around 148,9°C(300oF). The solids removal system associated to a low solids fluid, non disperse, without densifier, basically composed of bentonite/polyacrylamide/potash have been considered as important factors for drilling with density inferior to 1080Kg/m 3 (9.0 Ib/gal), during all phases of the drilling process.

Preventive treatments are the best method to avoid Preventive treatments are the best method to avoid contamination. However, if it occurs, it is necessary to restore the original properties off drilling fluid by addition of chemicals after the contamination. The changes in the drilling fluids properties, determined by regular test at specified intervals, will indicate the type and degree of contamination and required treatment. This paper Presents a software which identifies various contaminants from the analysis of their properties during drilling operations. A TURBO PASCAL program was developed using some artificial intelligence techniques. This program, named SIC (System for identifying Contaminants), verifies, for each usual contaminant, the possibility of its degree Of influence on each drilling fluid property. Introduction The aim of the present system is to aid in taking decisions for solving the occurrence of contamination of the employed drilling fluid during oil well drilling. By contaminant there is understood any naturally occurring or manufactured material, which is part of the fluid composition without any deliberate intention, altering one or more of the properties of same. properties of same. The well drilling activities require a swift action in deciding due to factors mainly concerned with security and cost. The knowledge of physical-chemical aspects of subsurface formations, especially in recently discovered areas, is limited. The control of drilling fluid's properties, by periodical physical and chemical tests, permits to keep these properties within programmed time schedules. As determinated by this monitored schedule, the alterations in fluid's behaviour will show in advance the type, degree of contamination and the treatment required for this kind of fluid. Preventive treatment is the method for avoiding contamination. Notwithstanding once same occurred, it is necessary to restore fluid's original properties. The most common preventive treatment consists in adding certain monovalent and polyvalent salts and/or bases. The treatment is known as "fluid conversion" because it transforms the non inhibited fluid in an inhibited fluid, making same immune to the action of some contaminants. P. 79