Contamination of drilling fluids

Potentially hazardous substances can arise from the formations being drilled. This is not always predictable. This section introduces some examples of more common contaminants.

Hydrocarbon-based contaminants

As the purpose of drilling a well is to produce hydrocarbons, one known source of hydrocarbon contamination will be from the reservoir formation. Often, however, the formations drilled through to the reservoir also contain hydrocarbons, but not of producible or commercial quantities. These hydrocarbon sources can introduce oil, condensate and gas contamination in a drilling fluid. Gases from formations are primarily composed of methane.

Non-hydrocarbon gases

Formations can contain hydrogen sulphide (H2S) gases and H2S-containing water samples. These gases must be closely monitored and treated to eliminate hazardous exposure to personnel. Both H2S gas and water contaminants in a drilling fluid system must be treated out, as the H2S can degrade the metal piping and tubulars of the circulating system.

Other gases

Carbon monoxide can be present particularly when coal beds are drilled.This occurrence is, however, extremely rare.

Low specific activity (LSA) radioactive scale contamination

LSA scale contamination of a circulating fluid can occur during scale clean-out operations, or when abandoning production wells. Operators should be conscious of this risk and control exposure as appropriate. Reference should be made to OGP report no. 412, Guidelines for the Management of Naturally Occurring Radioactive Material (NORM) in the oil & gas industry40.

These contaminants are either removed or treated in the drilling fluids used. Therefore, even though there may only be limited exposure from these contaminants, their identification and remediation at the earliest opportunity is important.

+1 0

Post a comment