Wax Predictions

The wax present in crude oils consists mainly of paraffin hydrocarbons (C20 – C40) and naphtenic hydrocarbons (C30 – C60). Under certain conditions of temperature and pressure, these components will come out of solution and form crystals of wax. In addition, waxy crudes also contain a variety of other compounds, such as light and intermediate hydrocarbons and heavy organics (resins, asphaltenes, diamondoids).

The deposition of wax in pipelines can eventually lead to the pipeline becoming blocked and unable to transport production fluids. It is usually the case that pipelines are designed to operate at temperatures above the crude oil wax appearance temperature (WAT). Fluid temperatures are maintained by the application of insulation to conserve heat. However on occasions, wax deposition is prevented by the injection of special chemicals called ‘wax inhibitors’ that help to maintain the wax components in solution. In addition, many crudes contain only relatively small concentrations of wax components such that protracted periods of operation may elapse before the pipeline becomes blocked. Under these circumstances, the operator may elect to allow the pipeline to build up wax, preferring to periodically clean the pipeline in one way or another (usually by pigging).

To strengthen Maximus Flow Assurance capability, we have also accessed MULTIFLASH’s wax formation methods. Hence, it is possible in Maximus to predict the boundaries between regions where wax solid will and will not form. This allows designers and operators, to define envelopes of safe operation that avoid problems associated with wax. This feature provides particular benefits in the design and operation of production systems that gather together fluids with different waxing potential. If the separate wellstream fluids are adequately characterised, then Maximus is able to predict whether wax will form in downstream pipelines containing commingled fluids. This is a common scenario which is easy to assess with Maximus but which presents difficulties for other commercially available software.

Below is an example of a phase diagram generated using the MULTIFLASH methods integrated in Maximus. The diagram was generated using a live oil composition and shows the wax formation curve crossing the bubblepoint curve. Wax is predicted to form to the left of the boundary shown.

Example Phase Diagram showing Wax Formation