Significant deepwater developments continue to be developed worldwide using subsea architecture. As is the case with nearly all upstream oil and gas production systems, flow assurance plays a significant role in asset development. In the case of ultra-deepwater, the role is a major one involving significant capital investment and associated operating costs. It is important that the flow assurance strategy for new ultradeepwater subsea fields encompasses ALL aspects of flow assurance and that lessons from other fields have been transferred properly.
The field discussed in this paper, Mica, is the longest tie-back in the Gulf of Mexico and has been in operation for over 4 years. The Mica wells are tied back via two 29 mile flowlines (one for gas and one for oil) to a major facility (Pompano). A recent review of Mica, comparing original flow assurance design strategies to current operational strategies has revealed several learnings. In particular lessons involving paraffin, corrosion, erosion, hydrates, and slugging will be discussed. Evaluation of a hydrate plug incident in the gas flowline provides insight on how hydrate plugs form as well aspotential operating strategies to avoid plug formation.
Mica (50% ExxonMobil, 50% BP) is located in the Gulf of Mexico in 4350 feet of water with first productioncommencing in 2001. It was decided early on that the Mica wells would be tied back to an existing platform, operated by one of the partners in Mica (BP).
Reservoir: Three separate zones in the reservoir were deemed producable. The shallowest zone (~10500 feet TVDSS) is a saturated gas and oil zone with a GOR of 1330 scf/stb, gravity of 32 API, and a wax cloud point of 93-100°F. The middle zone (~12000 feet TVDSS) is a near critical fluid with a GOR greater than 3000 scf/stb, gravity of 37 API, and a wax cloud point of 90-94°F. The deepest zone (~14500 feet TVDSS) is a dry gas with a condensate to gas ratio of 5 stb/mmscf and gravity of 44 API. Peak capacity from the reservoirs was expected to be 150 mmscf/d gas and 15000 stb/d oil.
Pompano Tie-In: Pompano is located 29 miles from the drill center for Mica (see Figure 1). Pompano is a steel jacketstructure in 1290 feet of water. Weight on the platform was not a major issue so it was decided to construct a new process system for the Mica wells. Since a relatively small amount of oil was expected compared to gas, a separate gas export pipeline was built for the gas while the oil was tied into the Pompano Crude Treater. New equipment built for the Micawells include a high pressure separator (HP), intermediate pressure separator (IP), low pressure separator (LP), turbine driven centrifugal compressor, a glycol dehydration system, and a turbine driven generator. Figure 2 shows the process system. The compressor draws suction from the IP separator at 450 psig and discharges to the gas export line at 1300 psig.