Acidizing High-Pressure Water Injection Wells Using a New Low-Damage Acetic/HF Acid System

摘要

A significant loss of injectivity was observed in some of thernhigh-pressure water injection wells on the Chunhua Oilfieldrnthe east of China due to severe formation damage, believed tornbe caused by fines and clay. This paper details the results ofrnmatrix acidizing treatments carried out in Chunhuarnsandstones, using a new low-damage acetic/HF acid system.rnThe new low-damage acetic/HF acid systems, which will bernreferred to as “LDA-1”, can coordinate aluminum fluoriderncomplexes and buffer the spent HF fluids. The coordinationrnof aluminum fluoride complexes helps alter the aluminum-fluoridernequilibria, which minimizes the amount of AlF3 inrnsolution and forces the HF reactions to lower F/Al ratios. Thisrnsystem increases the effectiveness of the treatment andrnovercomes the damaging precipitation of aluminum fluoridesrnduring the HF reactions.rnA series of laboratory short-core and long-core flow testsrnhas been fully analyzed. Coreflood results showed that therncore permeability increased after the treatment. Permeabilityrnratio(final/initial)of reservoir cores exponentially increasedrnwith the acid injection rate. Acidizing returns in corefloodrnwere analyzed to better understand the chemistry involved inrnHAC/HF acidizing. Returned samples were analyzed withrninductively coupled plasma (ICP) and 19 F nuclear magneticrnresonance ( NMR) spectroscopy. The combination of ICP andrn19 FNMR determined fluoride distribution on silicon andrnaluminum in the samples and the extent of HAC/HF fluidrnreactions.rnThe case historie included in this paper is treatment carriedrnout on one formation in Chunhua Oilfield. The field testrnresults shows that LDA-1 mixture is able to generate severalrnfold increases in the injectivity of the wells. They includernremedial treatment carried out on zones which hadrnexperienced detrimantal results due to poorly-designedrnconventional HF acid stimulations.rnThe treatment of CHC23-22 well was monitored with arnreal-time monitoring program, that showed that the skin factorrnhas dropped from about 13 to –0.21. Following the treatment,rninjectivity of this interval increased from 0m 3 /d to 100 m 3 /d.rnThe real-time monitoring plot shows that the skin has droppedrncontinuously during the injection of preflush and LDA-1, whatrnhas proven to be effective for deep damage removal. ThernLDA-1 system treatment was able to increase the injectivityrnand sustain it for more than 6 months.