Control of Filtration Characteristics of Salt-water Muds

Abstract

The wall-building properties of salt-water drilling muds can be improvedmarkedly by the addition of:natural gums, such as tragacanth, karaya, andghattiseaweeds, such as Irish mossgelatinized starch. Results oflaboratory tests have been confirmed by field trials. For drilling operationsin which the mud becomes contaminated by salt, either through penetratingsalt-bearing rocks or by addition of sea water to the mud, the added costresulting from the use of one of the substances listed above is more thanoffset by freedom from stuck drill pipe and ease in running casing. Introduction It has been recognized for many years that oil production might be seriouslyhampered by infiltration of water from the drilling mud. As knowledge of themechanism of the wall-building process advanced, methods were developed forevaluating the filtration characteristics of muds. The wall-building properties of freshwater muds are commonly regulated bythe addition of bentonitic clays, or of agents to promote the dispersion of thenatural mud solids. When strata bearing soluble salts are encountered in thecourse of drilling, the salts are incorporated in the mud; the clay solids areflocculated and water loss is increased tremendously. Methods generally used incontrolling filtration of freshwater muds are no longer applicable. The problem of reducing water loss from salt-water muds is not confined toany particular area, but is acute in parts of West Texas. Salt beds severalhundred feet thick must be penetrated before the oil-bearing formation isreached. Since the formation drilled does not provide mudmaking material, it isnecessary to use large quantities of commercial clays, and even the bestcommercial clay does not afford relief from the problem of high filtration. A laboratory study has been made of methods of improving the filtrationcharacteristics of salt-water muds, and some of the methods have been used infield practice. T.P. 1351