Selection and Application of a Non-Damaging Scale Inhibitor Package for Pre-Emptive Squeeze in Mungo Production Wells
Authors: Graham G. M. , Gyani A. , Jordan M. M. , Strachan C. , McClure R. , Littlehales I. J. , Fitzgerald A. 
Published: December 2007

This paper presents the challenges of identifying and deploying a non-damaging non-aqueous scale inhibitor for pre-emptive squeeze into the largest dry producer in the BP-operated Mungo field.

In order to pre-empt potential downhole scaling & subsequent impact on production, the Mungo asset requested a non-damaging, pre-emptive squeeze option for application prior to water breakthrough. Scale inhibitor squeezes are usually deployed post water breakthrough and when scale is predicted to form as a result of the co-mingling of incompatible produced brines. On the other hand, pre-emptive squeezes are preferred either when scaling is predicted from the start of water breakthrough or when the time required to mobilise chemicals etc. for an intervention is too long, placing production at risk. For Mungo, both these last scenarios applied: the predicted scaling tendencies were severe and immediate on water breakthrough, and the difficulty in mobilising a support vessel etc. to perform the job required careful planning and time.

BP and their Mungo partners initiated a chemical selection test programme through their CMS provider to identify a non-damaging "Best in Class" chemical squeeze option for Mungo. The CMS partner with responsibility for chemical management of the Mungo asset organised an independent laboratory to screen commercially sensitive, "non-aqueous" products (non-aqueous carrier phase) from both their own product range and those of their competitors for potential application.

When assessing chemical performance, clear selection criteria were issued to all the participating chemical suppliers prior to commencing any laboratory work. The chemicals were required to: (a) cause minimal formation damage (or &lt;10% damage in core flood tests); (b) provide a maximum squeeze life (ca. 1 year was requested by the Mungo asset); (c) be compatible with the incumbent corrosion inhibitor (&gt;95% corrosion inhibitor performance was required); and (d) be compatible with Mungo brine. Other selection criteria also included environmental category, cost, impact on facilities, practicality of deployment and proven track record. This paper focuses on the main selection criteria (a) and (b).

Comparative core flooding tests presented in this paper demonstrate that only one application fell within the specification of &lt; 10% reduction in permeability. Having selected the least damaging non-aqueous chemical, further core flood tests were designed to simulate: (a) injection into a lower permeability zone of the reservoir (or potential formation damage effects in the near wellbore region); and (b) the impact of chemical shut-in or adsorption.

Two pre-emptive squeeze trials of a novel "non-aqueous" scale inhibitor have now been conducted in wells W168 and W163 on the BP Mungo field. The scale inhibitor was deployed by bullheading, using injection quality base oil as a preflush and overflush. In neither case was formation damage seen as a result of the treatment, with no change in oil or water rates pre and post-squeeze.

In summary, the paper discusses how BP, Mungo partners and the CMS providers worked together to find the best technical solution to an important challenge facing many other fields and new developments, i.e. how to effectively select and deploy a non-damaging pre-emptive scale inhibition squeeze treatment. Independent testing has enabled the selection and deployment of a highly commercial "non-aqueous" application from an alternative non-CMS service provider.