The Haltenbanken area is environmentally sensitive due to its plentiful fish reserves and licensees are therefore faced with stringent guidelines for the use of chemicals. The Heidrun Field is located within the Haltenbanken group consisting of Heidrun, Asgard and Norne. All are relatively new developments. The reservoir has a bottom hole temperature of 85°C and a relatively low reservoir pressure of 250 bar, hence seawater injection for pressure support has been utilized. With Ba2+ levels in the range from 100 to 300ppm, downhole sulphate scale deposition was identified within the formation and the gravel pack. This has been highlighted by the active squeeze campaign since spring 2000 when seawater first broke through. Different generic scale inhibitors, including one biodegradable scale inhibitor, have been deployed in the field so far.

Due to the environmental sensitivity of the area, the scale control strategy has focused on the selection of environmentally friendly, or green, scale inhibitors. Moreover, the selected green inhibitors as well as exhibiting good performance and a long squeeze life, must overcome the severe emulsion formation experienced topside during initial flowback.

In this paper, the laboratory evaluation of potential green scale inhibitors is presented and some novel inhibitor test methodology is discussed. For example, the effect of temperature on inhibitor efficiency was found to vary when the cooling method was compared with the standard method where the test sample was pre-set to a target temperature. The cooling method was therefore found to better simulate field conditions where the fluid experiences temperature drops as it travels from the formation to surface. Also, in the inhibitor adsorption/desorption study, the static beaker tests were found to be an effective method of testing inhibitor adsorption properties for quick screening. While traditional beaker tests focus on the inhibitor adsorption, the inhibitor desorption property is usually studied using core floods. In this paper we shall present a new methodology based on bulk desorption tests. This has been used, in addition to the conventional core test, for our chemical selection. The field inhibitor squeeze return data demonstrated that the newly selected inhibitor offered an improved squeeze life than that previously experienced on Heidrun.

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