Abstract

The research program is based on earlier evaluation of seven different polyamino carboxylic acids (NTA, EDTA, DCTA,

DTPA, DOCTA, HEDTA and TTHA). The flow tests comprised the study of NaOH, KOH, Na2CO3 and K2CO3 solutions with and without dissolvers. Low molecular weight amines (mono-, di- and trimethyl and -ethylamines) served also as pH controlling agents. Comparison of inorganic and organic additives was made through their effect on effective permeability in artificially consolidated sandstone cores.

Based on the experimental findings it was concluded that solutions containing inorganic alkalis deteriorate the permeability independently of the fact that they were chelate containing or chelate-free. Similar results were obtained for all ethylamines. The methylamines, however, proved to be excellent pH controlling agents: permeability of the porous media remained unchanged, or even improved through extensive injection period; meanwhile the dissolution capacity of dissolvers was preserved or slightly increased.

It was clearly proved that selection of the best dissolver should be made by compromising the different technical aspects: not the chelating agent and the dissolution capacity is important, but also to the type of alkali compounds. Usingorganic alkalis the detrimental side effect of conventional inorganic alkaline compounds can be eliminated improving the flow characteristic and placement efficiency of dissolvers.

Introduction

Deposition and precipitation of barium and strontium sulfate in vicinity of wells and surface facilities often represents serious deterioration of producibility and injectivity in oil and gas production. Although extensive studies have already been made in order to elucidate the sag and scale formation mechanisms and a great variety of squeeze materials and dissolvers have been and still is investigated, the basic problems of acid insoluble BaSO4 and SrSO4 can not be considered as comfortingly solved even today.

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