LWI Operation Summary
This article discusses the challenges that can be encountered during wireline operations – including Light Well Intervention (LWI) – related to mixed mineral/organic deposits in the water injection wells named Black Sticky Stuff. The specific case history referred to here, was an intervention conducted by the LWI vessel Island Constructor (Figure 1) to install a deep set plug in the Tordis K-3 HT3 water injection well.
A frequent problem encountered during well intervention operations in water injector wells is that of obstructions and toolstring contamination caused by mixed mineral and organic deposits – commonly referred to as Black Sticky Stuff (BSS).
Over the years, LWI has experienced some of its most challenging problems in operations performed on water injectors due to this phenomenon. Developing a new approach, utilizing chemicals for removal of BSS, has allowed LWI to increase the operational envelope by improving the downhole conditions in water injectors.
The BSS formation mechanism is not fully understood, but recovered samples from several wells have been analyzed. A high content of iron oxides is found to be the main component, mixed with organic compounds which bind the material together into highly viscous dough. The BSS recovered from Tordis K-3HT3, consisted mainly of Fe3O4 (magnetite). The exact composition can vary from well to well.
An example of how these problems can develop may be obtained by comparing two LWI operations on the same well, Tordis K-1 HT5, in 2007 and 2012. The observed wireline friction factor increased from 0.26 in 2007 to 0.60 in 2012 in the same well due to continuous injection. The 2012 operation had to be aborted since it was not possible to reach target depth due to the high friction. It was therefore necessary to take these experiences into account when planning the intervention in Tordis K-3 HT3. The contingency plan was to treat the well with Pureclean Power and Pureclean Gold. These chemicals are water based mixtures of biodegradable substances and microbes designed to remove pipe dope and grease. The chemicals work by dissolving the organic binding material in the BSS, thus causing the deposits to disassociate and be swept clean by the flow in the well.
LWI Operation Summary from Tordis K-3 HT3
During the first WL run in K-3 HT3, the measured friction factor was 0.60 and the toolstring got stuck at 1000 mMD due to the BSS. A mixture of 40 m3 of Pureclean power (50%) and sea water (50%) was pumped, soaked and displaced into the well in two stages, with 1.5 hours soaking intervals before the entire well volume was displaced. On the second wireline run, the friction factor was reduced to 0.25 but the toolstring could not pass 1885 mMD. A new mixture of 48 m3 of Pureclean Power (25%), Pureclean Gold (25%) and sea water (50%) was mixed, pumped and was left to soak for 4 hours. On the third wireline run the deep set plug was set at target depth of 2750 m MD, with a reported friction factor of 0.20.
Pureclean Power and Pureclean Gold fluid treatments are found to provide an effective solution for dealing with BSS deposits during LWI operations. It is recommended that the use of these chemicals is evaluated in other operations, where this type of problem is experienced.
Authors: Shiblee Kamal, Dag Birger Solberg, Quentin Delot, Gea Sønstabø.