Asphaltenes are high molecular- weight aromatic polar compounds containing carbon, hydrogen, oxygen, nitrogen, sulfur and may also contain heavy metals such as vanadium and nickel.
Waxes are naturally occurring >C18-saturated linear and branched alkane molecules that are found in most liquid crude hydrocarbons. These components are completely soluble in the hydrocarbon under virgin reservoir conditions.
The Wax and Asphaltene components are not discreet molecules, but rather occur as a mixture of n-alkane-saturated hydrocarbons in the order of C18-C40, and even higher carbon chain lengths when branched. The presence of Wax and Asphaltenes does not indicate the potential for a Wax and Asphaltenes problem, and most Asphalty crudes are produced without precipitation or the need for chemical or physical treatment.
Waxes and Asphaltenes can deposit in reservoir, wellbore tubing, flowlines, separators and other parts of hydrocarbon production systems. These deposits can interrupt and potentially stop production due to formation of plugs. Other operational issues related to the precipitation of asphaltene include stable crude oil emulsions, higher emulsion viscosity and migration of asphaltene in to water phase leading to produced water treatment issues.
Waxes and Asphaltenes can become problematic when the fluids are subjected to various physical changes required to produce and separate the crude oil or condensate. Three physical processes in particular encourage precipitation of Waxy and Asphalty fluids:
- Pressure change
This causes the light ends of the crude oil to vaporize, reducing the overall solubility of the high Molecular Weight Wax and Asphaltenes in the remaining liquid hydrocarbon, which can lead to precipitation. Strong pressure changes occur at the formation face, chokes/valves, the wellhead and separators - Temperature change:
Cooling of the crude oil reduces the solubility of the Wax and Asphaltenes, which start to associate with themselves and crystallize from solution, observed as a cloud point. Particularly problematic locations can be oil storage vessels and flow lines, especially long-distance sub-sea tiebacks. - Turbulence:
Perhaps due to temporary degassing of fluids and impingement of Wax and Asphaltene crystallites on pipe walls, high turbulence flow areas are also known to be problem areas for Wax and Asphaltene deposits. Typical examples can be downhole pumps, treatment vessels, wellheads and chokes.
Once system temperature falls below the cloud point, wax has the potential to deposit and will require some form of control. Wax and Asphaltene begin to appear by forming needle-like or plate-like structures, and is initially observed as a cloud point in the produced fluid. These deposits can be very different in nature from system to system. Some form mushy, readily dispersed deposits, others form hard Waxy and Asphalty deposits – the latter being more problematic from a remediation perspective.
Treatment options
A range of mechanical and chemical options is available to treat asphaltene deposition issues. Mechanical cleaning methods include pigging, wireline, cutting and coil tubing options. While chemical treatment include the injection of inhibitors. This inhibitor is a polymeric compounds that stabilized the micelles and prevent the asphaltenes from flocculating.
This Product interacts with the asphaltenes to stabilize the asphaltene micelles in the crude oil. The asphaltene inhibitors possess stronger association with the asphaltenes and are able to stabilize the asphaltene through greater changes in pressure, temperature, shear and chemical environment. This Product can be squeezed into the batch or continually injected downhole. Squeezing the inhibitor into the reservoir can prevent deposition of asphaltenes in the near wellbore area.
It is important that This Product is added to the crude oil before the asphaltenes become destabilized and flocculation occurs.
In general, hard Waxy and Asphalty deposits forms from the higher C-chain length linear alkanes – typically >C25 n-alkanes and above. These problem high molecular- weight Waxes and Asphaltene are more prevalent in crude oil than condensates. The principal concern with Wax and Asphaltene deposits is the restriction of fluid production rates. This may be due to Wax deposition in the near-wellbore, restricting flow of hydrocarbon into the well, or more often deposition in production pipe work leading to restriction of diameter and therefore flow rate. Also the Waxy crystallites, if precipitated in the bulk hydrocarbon, can increase the viscosity of the fluids, reducing pipeline throughput. At worst, if the Wax and Asphaltene crystal network is allowed to continue to grow and fuse, such as during a shut-in, Wax gelling can occur and it may be impossible to reinitiate fluid flow, causing the pipe to be abandoned.
Wax and Asphaltene Treatment and Removal
This Product prevents the formation of Wax and Asphaltene through the use of different types of inhibitors.
Recently, Wax and Asphaltene inhibitors are one of the most widely – used chemical mitigation techniques in treating deposition issue. Acting as a Wax and Asphaltene inhibitors, they are incorporated onto the face of a growing Wax and Asphaltene crystal, interrupting its structure changing its formation rate and thereby reducing the formation of three dimensional network. The Wax and Asphaltene inhibitors must have sufficient compatibility with the host crystal to adsorb onto the surface to disrupt subsequence crystal growth.
Performance
It is well-known that the performance of Wax and Asphaltene inhibitors are oil-specific. We should consider a product that works well on one type of oil may not work well on other fluids. This is partially contributed to the presence of organic acids in the oil. Therefore, it is very important to use the actual asphaltene inhibitor during production. If not chosen properly, some inhibitors can actually make the asphaltene problem worse by precipitating more asphaltenes compared to an untreated system.
Advantages
- Reduction the oil viscosity
- Reduction in heating demands resulting in energy saving
- Maintained fluid flow through the pipeline
- Proven performance in a variety of crudes
- Reduction in solid build up
- Reduced toxicity: not carcinogenic, repro-toxic or toxic to organs
- Reduction in deposition of solids which helps to maintain production.
- Lower pumping pressure due to reduced viscosity
- Maximize production potential by preventing deposition/restriction in flowlines and tubulars;
- Preserve asset integrity and reliability of subsea wells and flowlines
- Optimize performance of surface treating operations, maintaining throughput and minimizing down time.
