Drilling fluids are essential chemicals that are used for any oil well exploration activities like removal of cuttings from underneath the borehole, suspend and transport cuttings, lubricate the drilling surface, etc. There are some minimum properties of Oil Well Drilling fluids that need to be maintained in order to make the drilling fluid an effective tool to carry out various drilling functions. A mud engineer caters a status report, in which he outlines the properties of the fluid and how it reacts with the subsurface environment and it mainly outlines the critical drilling fluid properties like density, chemical composition, fluid loss control, viscosity, etc.
Amongst these, density is the most crucial property that has to be measured and maintain effectively.
One of the main functions of an oil drilling fluid is to impound the fluids formed during drilling to their surface beds and the density that it needs in order to effectively carry out this function is dependent on the subsurface formation pressures. Low-pressured, strong formations can be drilled out with a fluid with density less than 1.0, but high-pressured shales and formations may require a fluid with densities in the range of 2.4. The density of such fluids can be adjusted by soluble salts additives.
Different types of base drilling fluids like Calcium Bromide (CaBr2), Sodium Bromide (NaBr), and Zinc Bromide (ZnBr), because of their high density characteristics, are widely used for drilling purposes. CaBr2, a clear brine liquid is used as a single salt brine in densities ranging from 11.7 lbs/gal to 15.1 lbs/gal. It is used as a single-salt or a spike fuel that increases densities of other fluids up to 14.2lbs/gal. NaBr, a salt is used alone or in a combination with sodium chloride or other bromides to form clear workaround and drilling fluids with densities of 8.4-12.5 lbs/gal. ZnBr, a solids-free fluid has a maximum density of 19.2lbs/gal. . It can be used with other bromides and chlorides to prepare non-damaging liquids with densities ranging from 15.1 lbs/gal to 19.2 lbs/gal. Thus, these various salts are used as single-salt or multi-salt additives to achieve the correct densities needed to drill oil and gas and control the formation fluids.
Another important property of the drilling fluids is brine composition:
While the above bromides serve as good high density drilling fluids, a combination of these fluids with each other or chlorides form excellent multi-salt liquids that form excellent drilling, completion, and packer fluids. Such a brine composition serves to form the exactly needed densities that are needed to drill formation liquids. The various multi-salt brine compositions that are widely used are:
Zinc Bromide/Calcium Bromide mix: It is a clear, solids free brine fluid of 19.2 lbs/gal density, with 53-58% ZnBr2 and 20.0-23.0% CaBr2. It can be blended with other solutions containing bromides and chlorides.
Calcium Bromide (CaBr2) /Calcium Chloride (CaCl2) mix: It is a two-salt brine system ranging from 11.7 to 15.1 lb/gal densities. This density range is obtained by blending 11.6 lb/gal CaCl2 with 14.3 lb/gal CaBr2.
Sodium Chloride (NaCl) /Sodium Bromide (NaBr) mix: It is a clear brine fluid that is formulated to meet and crystallization temperature requirements and individual density, covering the density range from 8.4 lb /gal to 12.7 lb /gal. This blend is often used when the calcium ion is not desirable.