This article discusses the practical application of low solids non-dispersed drilling fluid related to Cotton Valley drilling operations. A low solids system is briefly defined and proper solids control equipment and maintenance techniques are discussed. In conclusion the paper discusses mud related Cotton Valley drilling problems and presents examples of field data problems and presents examples of field data showing the favorable results achieved with a low solids mud system in several Cotton Valley wells.


Drilling activity in the East Texas Cotton Valley Play has increased steadily over the past several years. The high level of activity has brought many new drilling techniques including low solids mud into Cotton Valley drilling operations. Many Cotton Valley operators have been using low solids non-dispersed polymer muds to help increase their drilling efficiency. However, the benefits of low solids non-dispersed polymer muds are often not fully realized because of insufficient planning and improper field practices. planning and improper field practices. It is generally accepted by the industry that the drilling fluid is the single most important factor affecting drilling rate. Acting upon this theory, we have researched low solids muds for many years and have successfully applied them to over 100 Cotton Valley wells. Through the use of low solids mud we have realized a substantial saving in our Cotton Valley drilling operations which has helped offset the steady inflation of drilling costs.

This paper attempts to share some practical Cotton Valley drilling experience with the industry. Proper solids control is discussed along with recommended guidelines for maintaining low solids mud properties. The paper also outlines proven techniques for dealing with some typical Cotton Valley drilling problems and shows some examples of Amoco's success using low solids non-dispersed polymer muds.


A low solids non-dispersed polymer mud is a fresh water based drilling fluid having a drilled solids to bentonite ratio (DS/B) of less than 3/1 and containing no chemical dispersants.

Since all types of solids adversely affect penetration rate, both the commercial and the penetration rate, both the commercial and the drilled solids content of the system must be minimized. However, mud making solids like bentonite are necessary in most drilling operations to help clean and protect the hole. Therefore, bentonite extending polymers are used to achieve the same mud properties with a lower concentration of the commercial solids. The drilled solids content is controlled with the various solids removal methods and equipment discussed in the following section. The DS/B ratio is used to indicate the efficiency of the solids control program.


Drilling mud research has determined that drilled solids less than 1–2 microns are 12 times more detrimental to penetration rate than those larger in size. Drilled solids must therefore be removed from the system before they have a chance to become finer with circulation. Rigs contracted to drill with low solids non-dispersed polymer muds must be equipped with certain essential solids removal equipment to realize maximum benefit from this mud system. Figure 1 graphically illustrates the random particle size distribution as a function of percent of each size range normally found in a typical drilling mud. The figure also shows the normal solids size range that each piece of solids control equipment operates in. In addition to having all the proper equipment, it must also be hooked up in the proper order. Figure 2 illustrates a logical equipment layout for efficient solids removal. This layout will insure that each piece of equipment is treating the entire system and there by reducing the solids load on each subsequent piece of equipment for increased efficiency. Following is a list of necessary solids control equipment and some recommended operational guidelines.

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