Preparation and performance evaluation of a highly effective barium sulfate descaling system based on ammonium carboxy chelating agent DTPA

Abstract

In drilling and production process, the barite powder serving as weighting agent is added to ensure operation safety when overflow occurs, that results in reservoir pollution and pore blockage. The main component of barite is BaSO₄, so ammonium carboxy chelating agents can be injected into formation to form stable chelates with Ba²⁺, BaSO₄ will be eliminated from wellbore with flowback fluid easily. In this experiment, the weight method and the atomic absorption spectrometry method were utilized to study descaling ability and an action mechanism of descaling agents. Firstly, DTPA was selected from three descaling agents: NTA, EDTA, DTPA; then OT1 was screened out to synergize with DTPA and studied its descaling mechanism; eventually, the descaling system STD was determined, and its composition was 6% DTPA + 5% OT1 + 1% antiswelling agent + 100 ppm corrosion inhibitor. And the STD’s performance evaluation experiment results suggested that it had an excellent resistance to temperature and demonstrated a good descaling ability at 170°C. Furthermore, the descaling ability of STD was almost not affected by calcium and magnesium ions and its corrsion rate is lower than standard value. Moreover, STD could descale efficiently at lower dosage. So STD can be widely applied to descale in oilfield.