Asphaltene Case Study

2.14 ASPHALTENES PROBLEMS

From an organic chemistry standpoint, they are large molecules comprised of polyaromatic and heterocyclic aromatic rings, with side branching. Asphaltenes originate with the complex molecules found in living plants and animals, which have only been partially broken down by the action of temperature and pressure over geologic time. Asphaltenes carry the bulk of the inorganic component of crude oil, including sulfur and nitrogen, and metals such as nickel and vanadium. All oils contain a certain amount of asphaltene (Ellison et al., 2000). Asphaltenes only become a problem during production when they are unstable. Asphaltene stability is a function of the ratio of asphaltenes to stabilizing factors in the crude such

Typically problems only occur downstream due to blending or high heat. Crude oils with unstable asphaltenes suffer from some severe operational problems, most of which are fouling related and affect valves, chokes, filters, and tubing. Asphaltenes become unstable as the pressure of the well decreases and the volume fraction of aliphatic components increases. If the aliphatic fraction of the oil reaches a threshold limit then asphaltenes begin to flocculate and precipitate. This pressure is called the flocculation point. Figure 2.24 shows the effect of pressure to the asphaltenes stability. In the left hand of the curve, asphaltenes are unstable, while to the right of the curve, asphaltenes are stable (Edmonds et al

This generally gives rise to carbonate scales. Also, when two incompatible waters for example, formation water rich in calcium, strontium and barium and sea water rich in sulphate, mixes together, forms and deposits scales under supersaturated condition. This generally gives rise to sulphate scales (Time 2011). The deposited scale adheres on the surface of the producing well tubing and on parts of the water handling equipment, where it builds up with time and leads to flow assurance problem in reservoir, pumps, valves, topside facilities and subsea