PREVENÇÃO DE INCRUSTAÇÕES INORGÂNICAS NA EXPLORAÇÃO PETROLÍFERA OFF-SHORE: ASPECTOS ANALÍTICOS E APLICAÇÕES DO INIBIDOR PPCA / PREVENTION OF INORGANIC SCALE FORMATION IN OFF-SHORE OIL EXPLORATION: APPLICATIONS OF THE PPCA INHIBITOR

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

In the present study, a system was developed for the automatized pretreatment of the inhibitor phosphinocarboxilic acid (PPCA) used during off-shore oil exploration to minimize the occurrence of inorganic scale formation. The components of the system used are: 3, 4 or 6 way solenoid valves with Teflon body, a home-made electronic circuit for activation of the valves, a peristaltic pump, a microcomputer and software (PRETRAT) written in Delphi. The electronic circuit, connected via the parallel port of the PC, has the function to reduce the supply voltage for the solenoid valves form 12 V to 4.5 V, thus permitting their uninterrupted use for longer periods of time. The power module of the microcomputer is used to obtain the supply voltage of the solenoid valves, while its serial port commands the peristaltic pump. The developed software program PRETRAT permits automatic control over all relevant parameters used in the pre-treatment procedure, including solution volumes and flow rates. This pre-treatment, mandatory due to the high salinity of the produced water and its elevated concentrations of inorganic phosphorus, was achieved by separating the organic phosphorus (contained in the PPCA molecule) by using silica-C18 columns (SEP-PAK classic, 360 mg). Optimization of the pre-treatment procedure resulted in the following experimental parameters: (1) conditioning of the column with methanol 80% v/v; (2) percolation rates of 5 mL.min-1 for conditioning, sample throughput and elution; (3) elution of organic phosphorus with 3.5 mL of a buffer solution of H3BO3 0.025 M (adjusted at pH 9 with NaOH 0.2 M). The quantification of the PPCA inhibitor was performed indirectly by measuring its phosphorus content by on-line inductively coupled plasma mass spectrometry (ICP-MS) and/or by optical emission spectrometry (ICP-OES). Detection limits (3 ) in the borate matrix (0.025 M) were 0.20 g.L-1 e 92 g.L-1 for ICP-MS and ICP-OES, respectively, using in both methods a cross-flow nebulizer and a Ryton spray chamber. Recoveries of organic phosphorus were, typically, in the range of 90% to 95%. For assessing the repeatability of the procedure, eight sample replicates containing each 0.40 mg.L-1 of phosphorus as inhibitor were processed under the conditions already mentioned, resulting in a mean recovery of de 0.42 +/- 0.02 mg.L-1 and a relative standard deviation of 4.8 %. This value compares advantageously with the mean reproducibility of about 25% obtained by a manual pre- treatment (Rocha, 1997). Frequency of analyses is about six samples per hour using a pre-concentration factor of 10 and a sample volume of 35 mL. The automatized pre- treatment method was applied for comparing the behavior of commercial inhibitors during field use and in laboratory studies on the adsorption/desorption characteristics of PPCA on rock samples, simulating the squeeze process. Produced waters from four wells, in which the squeeze process was applied, were analyzed by the here-developed method, permitting the follow-up of PPCA release and the observation that some of the used inhibitor lots did not perform adequately during the squeeze process. Speciation analysis of inorganic and organic phosphorus in those lots revealed significant differences in composition when compared to well performing ones, also confirmed by ion chromatography. This methodology has demonstrated efficient for quality assurance of inhibitors prior to their application.

ASSUNTO(S)

scale inhibitors automation of pre-treatment procedures for ppca determinacao de fosforo determination of phosphorus inibidor de incrustacao automacao de pre-tratamento para ppca

ACESSO AO ARTIGO

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