SAGD short stories: The “LACT” word!
“SAGD short stories” is a blog series about SAGD and process operations.
Retail businesses use modern cashier stations with bar-code scanners and weigh scales to take care of sales. But in the oil production business, including SAGD producers, this function is performed in a LACT, or Lease Automatic Custody Transfer unit (LACT is pronounced as a word, rhymes with pact).
At a basic business level, a SAGD production facility is a vendor, very simply a buyer and seller of goods. And just like every vendor, the SAGD producer has to accurately control and record all sales transactions. The LACT unit performs Custody Transfer Metering to ensure accurate recording of the quantity and quality of crude oil and petroleum products transferred between production facilities and pipelines, and vice versa. Thisis critical for transferring ownership because, once oil leaving a production facility enters the sales pipeline, the pipeline company takes ownership.
Custody Transfer Metering of SAGD Sales Oil is done before the oil is shipped through the pipeline to customers. A SAGD LACT unit typically monitors and records sales oil density, viscosity,
A SAGD production facility typically receives Diluent
from a pipeline, and the LACT unit also handles this too.
Custody Transfer Metering of Diluent is done as diluent flows from the pipeline to the facility. It is common for incoming diluent to be used to fine-tune the viscosity of the outgoing sales oil flowing through the LACT unit. A process loop measures the sales oil viscosity and automatically blends in diluent to maintain a set point viscosity for the finished blend.
A SAGD producer typically has its own parallel sampling and metering systems for sales oil and diluent, which is normally located and housed just outside of the production facility boundary. This allows the pipeline company to routinely visit and remove sample bottles of the sales oil for additional testing, and to calibrate the equipment to ensure ongoing accuracy.
The recorded values generated by the SAGD producer are continually compared to those from the LACT unit for verification and to ensure agreement between seller and buyer.
Pipeline companies have Pipeline Quality standards to prevent corrosion or operation issues due to unknown product composition. SAGD sales oil must meet certain criteria to be considered as “pipeline quality”.
Examples of typical SAGD sales oil specifications include:
- BS&W (Basic Sediment and Water, or Watercut) content (i.e. 0.5% max.)
- Density (i.e. 940 kg/cubic meter @ 15ºC max.)
- Viscosity (i.e. 350 centistokes @ 4ºC max.)
- API Gravity (i.e. 16 max.)
- Temperature (i.e. 60ºC max.)
- Reid Vapour Pressure (i.e. 76 kPag approx.)
Note that exact specifications vary by customer and facility.
If any one of the measurement devices reports an off-spec result, the sales oil is typically returned to storage through a recycle loop automatically.
A SAGD sales oil LACT unit commonly includes a few other parts, such as oil degassing equipment or booster pumps.
To find out more about SAGD LACT units used in the Canadian Oil Sands, you can view the Sales Oil and LACT chapter of Contendo’s SAGD Oil Sands Online – Bitumen Processing Course.
Kevin Fox is a senior technical writer at Contendo.
He is a power engineer who has written process education programs for industrial clients since 2009.