Utilizing Integrated Network Model to Optimize Production and Prevent Halite Formation in Pipeline Offshore Gulf of Suez

Abstract

Scale deposition has always been an irritating problem for oil and gas industry. Scale typically results from a chemical state of supersaturation, which results from changes in pressure, Temperature & PH across production system. At this time precipitation reaction takes place and the mass of scale deposition is a function of the available amount of cation and anion species related to subject scale. Typical forms of scale are calcium carbonate & Sulfate, Strontium & Barium Sulfate. Commonly Deposition rate for such types of scales is quite slow due to limited concentration of relevant species. For the case of halite deposition chlorides salts are abundant species in water that in case of deposition would result in huge mass that may block tubing, flow lines and pipelines in short time. Subject Field is located offshore Gulf of Suez, rimary reservoir is Nubian sandstone at depth of more than 11000 Ft & Temperature of 330 F. Formation Salinity around 350,000 PPM. Typically, water is in equilibrium at reservoir conditions and high productivity of wells allows high wellhead temperature which keeps chloride salts soluble in water. The field produces through two 12" pipelines to a central processing facility. s the flow goes heat exchange takes place and soon balances with seabed temperature. Scale tendency calculations showed Halite would precipitate at 90 F. which means the vast majority of pipeline will be subject to the risk of halite deposition. This matches with a biweekly to monthly increase in line pressure impacting production due back pressure on producers and at critical point emergency shutdown would trip to protect line integrity. The problem has been persistent that shutdown was expected on monthly basis and logistics consumed to pump fresh water followed by soaking time and pigging to ensure line pressure kept to minimum otherwise it will not take long before line plugs again. In 2020 a detailed Network Model coupled with scale formation prediction tool to determine pressure and temperature profile in subsea pipeline and expected scale formation rate with distance from platform. Network optimization model showed that commingling specific wells on one line and keeping others on the other line would result in decreasing the risk of halite scale, investigations showed some incompatibilities between water from different wells that can be managed with scale inhibitor. Application of the outcomes from network model in the field resulted in maximizing production eliminating downtime due to line pressure increase and eliminated the need for biweekly fresh water pumping.