BS&W or Basic Sediment and Water is a term originally used to refer to the measurement of water and sediment (suspended solids) in crude oil production. Measurement can take place at the wellhead, tank or at custody transfer. Historically, such measurement was conducted with the use of a centrifuge. (See API MPMS Chapter 10.4/ASTM D96.) Today, the term is also used interchangeably with "water cut" – or the percentage of water in crude oil. BS&W monitors are also commonly called water cut meters.
It is important to make the distinction that water cut meters do not measure sediment. Sediment can only be measured by centrifuge or extraction (ASTM D473). However, most BS&W monitors or water cut meters will be placed after separators to measure water content for custody transfer. In these cases, sediment is generally not a concern.
There are three main types of BS&W monitors: capacitance, microwave, and optical. In order to determine the best option for measuring water cut, operators should have a clear understanding of the range of water content, the accuracy desired, and the flow conditions, such as velocity, viscosity, gas, density, etc. All BS&W monitors are not alike and different technologies suit different needs.
The most common BS&W application is custody transfer. Custody transfer occurs when crude oil changes hands. Common sites include the production lease; pipelines; and truck, rail, and marine loading and unloading. Custody transfer agreements dictate a maximum allowable water quantity and which is usually monitored in real-time by the BS&W as well as by automatic sampling for laboratory testing. Most LACT (Lease Automated Custody Transfer) units specify a BS&W monitor in addition to sampling and flow measurement. BS&W monitors provide real-time data that can alert operators to off-spec batches that can then be declined or rerouted, while laboratory data from the sampling is usually used for any legal dispute.
At the wellhead, BS&W monitors can be used to monitor produced water levels in real time, or off a test separator. This intelligence can be used to optimize and even automate field operations. For instance, operators can automatically shut in low producing wells based on specific criteria.
BS&W monitors or variations of them are also used in numerous tank applications such as interface detection, automated dewatering, and desalter optimization.
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