Development of an Environmentally Friendly Polymer Scale Inhibitor for Tight Carbonate Reservoir Squeeze Treatment
Authors: Chen Tao , Benvie Ronald , Heath Stephen Mark , Chen Ping , Hagen Thomas Hille , Montgomerie Harry 
Published: April 2012

A tight carbonate reservoir is one of the typical formations in the oil and gaswells. The unique feature of the subject reservoir is low permeability (2–5md). The formation damage, compatibility, residual analysis and squeeze lifeare still major challenges for the conventional scale inhibitor squeezetreatment in this kind of reservoir.

The development of effective squeeze scale inhibitors to prevent the aboveproblems in BaSO4 scale scenario is still a big challenge, especially with theincreasing environmental constraints. For tight carbonate reservoirs, theformation damage is one of the major considerations since the formation damagecan be caused due to fines mobilization, carbonate reservoir dissolution andcompatibility issues. For the development of any product for squeezeapplication, the product must also demonstrate good performance on field scaleinhibition, long squeeze life and accurate residual analysis at lowconcentration.

This paper will demonstrate a logical design procedure to develop anenvironmental friendly polymer scale inhibitor product suitable for challengingtight carbonate reservoir through squeeze application and will discuss themechanism of scale inhibitor retention with regard to selection and design ofsuitable scale squeeze inhibitors.

Many scale inhibitors are either irreversibly retained in chalk reservoirs dueto uncontrolled precipitation reactions or are poorly adsorbed with bothprocesses resulting in short treatment lifetimes. A new polymeric scaleinhibitor chemistry, containing a special functional amine group to have a goodaffinity to the chalk reservoir, was developed to provide a balance betweenirreversible and poor retention and thus provide effective squeeze life. Theresults of a comprehensive testing program, including compatibility, formationdissolution, dynamic tubing blocking, static adsorption and core flood testswill be presented, that will highlight the development of polymer scaleinhibitor suitable for the tight carbonate reservoir, while meeting theenvironmental requirements for application in the UK and Scandinavia. Inaddition, a new residual detection method will be presented which willdemonstrate accurate scale inhibitor detection at low concentration (&lt;1ppm)in high TDS water.

Introduction

Barium sulphate, BaSO4, is one of the most common scale deposits found inoilfields both in the North Sea and elsewhere. It can be deposited all alongthe water paths from injectors through the reservoir to the surface equipment1,2, 3. Barium sulphate is generally formed after seawater breakthrough, whenformation water containing barium mixes with seawater which is rich insulphate. Barium sulphate scale formation can impair production by blockage ofnear wellbore, tubing and flowlines, fouling of equipment and concealment ofcorrosion. The effects of scale can be dramatic and costs can beenormous4.

Effective techniques are needed to solve the scale deposition and keepproducing wells healthy. In most cases, scale prevention through chemicalinhibition is the preferred method of maintaining well productivity. Scaleinhibitor squeeze treatments provide one of the most common and efficientmethods for preventing the formation of carbonate and sulphate scales in thenear wellbore and top facilities of production wells3.