Composition, Properties and Field Performance of a Sulfonated Oil-Base Mud
Authors: Messenger Joseph U. 
Published: December 2007

Abstract
An oil-base drilling mud has been prepared by two methods:by sulfonating asphaltic crudes using concentrated sulfuric acid, and thereafter neutralizing with sodium silicate and ion-exchanging with hydrated lime; orby absorbing concentrated sulfuric acid on a porous carrier such as diatomaceous earth, sulfonating asphaltic crudes, therewith, partially neutralizing with sodium hydroxide, and thereafter ion-exchanging with hydrated lime.
By controlling the temperature of reaction and the composition of the drilling fluid, many different discrete particles of varying sizes can be formed in or added to the drilling mud. This degree of particle-size control results in a mud whose properties can be controlled over a wide range; the mud will drill gauge, stabilized hole in upper shales competitively with water, and is nondamaging as a primary completion fluid.

Introduction
To be precise, the drilling mud described in this paper is called a "sulfonated full oil-base drilling mud" because sulfonated asphaltic crudes constitute one of its primary components. More simply. it can be called a sulfonated oil-base mud. There is no reason to discuss in great detail the functions of a drilling fluid. A full oil-phase drilling mud must exhibit most of the properties and perform most of the functions of a good water-base mud system. The purpose of this paper is to discuss the properties that oil-base muds have in addition to these, particularly the properties and functions in which sulfonated oil-base muds excel. These additional properties must outweigh certain deficiencies of all oil-base systems for example, their inability to permit electric logging, the fact that they are disagreeable to use and, in some cases, their higher cost. To summarize a good oil-base mud:performs all the functions of a water-base mud or permits an acceptable substitute for these functions;has most of the desirable properties of a water-base mud;does not hydrate and disperse cuttings;will not dissolve salt or other water-soluble formation deposits and can be used to core such sections;exhibits good penetration rates;protects productive horizons;does not increase the interstitial water of cores; andis not affected by contaminants such as cement, anhydrite, salt or shale, and can tolerate contamination with water and raw crude.
In addition to these, sulfonated oil-base mud:is subject to some degree of built-in particle-size control and, therefore, tailored property control;exhibits surge-loss control andis low in cost.

Formulation

Mud Composition and Chemistry
To explain why sulfonated oil-base mud is mixed as it is and why (for the present at least) it does not come packaged in a sack so that it can be added to any oil, a brief account of what is formed during its mixing may be helpful. During its formation many discretely different particle sizes can be created within this mud system. Some degree of particle-size control is exercised by varying the nature and quantity of materials added. Further, by controlling the environment in which the reactions which form these particles take place, it should be possible to control the particle sizes even further. Particle size is affected by temperature even though its effects are not yet completely understood. That particle size can be controlled by controlling temperature and rate of reaction while forming sulfonated oil-base mud becomes visually evident as the temperature of reaction is increased. Between 115 and 120F, particles of silica become evident as "solid curds" before they re-disperse. Reactions become spontaneous and noticeably exothermic. Filter-loss passes through a minimum. Thus, sulfonated oil-base muds contain a range of particle sizes naturally associated with the products formed by reaction in the mud and varied to some extent by controlling the temperature. These particles can contribute greatly to the superior properties and performance of this drilling mud.The mud can contain sodium Invermul, calcium Invermul, sodium sulfonated asphaltenes, calcium sulfonated asphaltenes, possible silicon sulfonated asphaltenes, hydrated lime and colloidal silica.
JPT
P. 259^