The Assay of Chemicals for Oilwell Stimulation

Abstract

This paper was prepared for the Society of Petroleum Engineers of AIME Symposium on Formation Damage Control, to be held in New Orleans, La., Feb. 7–8, 1974. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract Mixtures of hydrochloric and hydrofluoric acids have been successfully used in the stimulation of sandstone reservoirs. Occasionally, however, an inadequate response to these acids results and in some cases additional well damage has occurred. This poor response may be partly due to the improper concentration partly due to the improper concentration of HC1-HF acid used in the treatment. Laboratory data show that the concentration of an acid formulation can have a significant influence on the results of a treatment. This makes the rapid and accurate assay of the acid solution to be used, an important factor in a successful treatment design. This paper will describe an analytical procedure that employs a mixed titrant in procedure that employs a mixed titrant in conjunction with ion selective electrodes and Gran's Plots to determine the amounts of hydrochloric and hydrofluoric acids in mixtures. The proposed procedure will be compared to other analytical methods and the effect of (other experimental parameters and contaminants will be discussed. It will be shown that the method can be routinely performed by semi-skilled technicians under performed by semi-skilled technicians under field conditions. The procedure was tested for precision and accuracy on laboratory and field prepared acid mixtures. Analysis of field mixtures using this procedure reveal that conventional field mixing methods do not always produce uniform solutions. Introduction The use of hydrochloric-hydrofluoric acid mixtures in matrix treatments of sandstone formations can be effective in stimulating production and injection wells. Occasionally however, an inadequate response to these acids results and in some cases additional formation damage occurs. This poor response may be partly due to the poor response may be partly due to the improper concentration of acid used in the treatment.