Scale Inhibitor Evaluation For Oil-Field And Geothermal Operations
Authors: Vetter Ottomar J. , Kandarpa Vivekandanda 
Published: December 2007

Very few publications on scale inhibitor evaluations can be found in the open literature. The published methods, one of which is by one of the present published methods, one of which is by one of the present authors, are very controversial and do not allow the impartial screening and/or evaluation of scale inhibitors. The methods suffer from a critical lack of reliability for two main reasons:The test conditions do not simulate the most critical field conditions.The analytical parts of these methods are not accurate enough.

An elaborate new study of practical scale inhibition is presently in progress. Various portions of this study are funded by private industry and the U.S. Department of Energy.

The study includes both laboratory and field evaluations of scale inhibitors. The main objectives of this new study are to develop test procedures and use these procedures for screening and evaluating large numbers of scale inhibitors. The relevancy of the test procedures and test data for field operations is emphasized.

The basic test strategy is to:Develop test procedures to screen available scale inhibitors in an economical way. The test conditions must cover a wide range offield conditions.Use the newly developed test procedures to screen a large number of available scalehibitors and generate a catalogue of inhibitor properties. This will allow a ranking of inhibitors for various field conditions.Develop test procedures to evaluate a limited number of the most potential scale inhibitors for site-specific applications. These most potential inhibitors are chosen from the screened inhibitors.Prove the entire test sequence byperforming a number of site-specific inhibitor tests and by performing actual field experiments.

Part I of this elaborate study is concerned only with laboratory determinations of the scale inhibitor efficiencies under an extremely wide range of simulated field conditions. Problems and solutions of efficiency determinations are described. A new test procedure suitable for routine screening of scale inhibitors has been developed. Thirty-four (34) scale inhibitors are presently being screened using this new procedure.

Introduction

Scale is one of the most annoying problems in the production of aqueous fluids from subterranean reservoirs. The operation of oil, gas, water, geothermal and leach mining wells are typically hampered by artificial flow restrictions due to scale formation. The scale deposits can occur anywhere in the subterranean reservoir, the wellbore sand/or in surface installations.

Sometimes, these deposits are so severe that the entire field operation is at stake within a very short production time. Geothermal wells are particularly prone to heavy scale build-ups. Quite particularly prone to heavy scale build-ups. Quite often, the problems are less severe at the beginning but the development of the problem will accelerate as a function of time or cummulative production due to the self-aggravating effects of scale deposits (see Figure I).

Scale deposits, no matter where they occur, can cause extremely costly remedial and preventive measures. In many instances, the damage caused by scale becomes irreparable, i.e. a heavy price be paid either for ignoring the problem or because of the frequent lack of effective counter measures. Most field operators are aware of their scale problems and are constantly searching for problems and are constantly searching for cost-effective methods to eliminate the scale or atleast to minimize its formation.