Drilling Solids Removal Theory -Basic Knowledge

Drilling fluid maintenance costs can decrease greatly when proper solids control techniques are utilized. From a fluid control standpoint, it would be desirable in most cases to remove all drilled solids. Although this is possible with the use of chemical enhancement prior to separation, it is not always the most economical approach. The goal of a solids control system is to achieve the balance between mechanical solids separation and dilution that will result in drill solids being maintained at an acceptable level with the minimum cost.

Drilling mud removal theory
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Fundamentals of Drilling Fluids

A major component in drilling operation success is drilling fluid performance. The cost of searching for hydrocarbon reserves becomes more expensive when drilling occurs offshore, in deep water, and in hostile environments. These drilling environments require fluids that excel in performance. Measuring fluid performance requires the evaluation of all key drilling parameters and their associated cost. Simply stated, the effectiveness of a fluid is judged by its influence on overall well cost. This chapter discusses the various fundamentals of drilling fluids and their performance in assuring a safe and expeditious drilling operation at minimum overall cost.

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Drilling Cuttings Separation

Mineralogy of Cuttings

Drill cuttings are particles of crushed rock produced by the grinding action of the drill bit as it penetrates into the earth. Drill cuttings range in size from clay-sized particles (~ 2 μm) to coarse gravel (> 30 mm) and have an angular configuration. Their chemistry and mineralogy reflect that of the sedimentary strata being penetrated by the drill.

Solids control equipment separating cuttings
Figure 1. Separation of WBM and cuttings is mainly based on particle size and relies on shale shakers, hydrocyclones (mud cleaner), and occasionally a decanting centrifuge. Most cuttings are sand/gravel-sized and are easily recovered on the shale shaker. However, silt- and clay-sized cuttings are difficult to separate from the barite and bentonite of WBM; hydrocyclones and centrifuges may be required.

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Use of traditional cuttings handling systems based on washing the cuttings. By cleaning the cuttings, the oil content in the cuttings can be brought down to approximately 100g oil content per. kg drilled cuttings, which is the average allowable discharge of oil per. well. This again means that the cleaned cuttings can be dumped to sea after cleaning is performed.