Druce K. Crump

Use of Highly Acid-Soluble Chelating Agents in Well Stimulation Services

Chelating agents are materials that are used to control undesirable reactions of metal ions. In oilfield chemical treatments, chelating agents are frequently added to stimulation acids to prevent precipitation of solids as the acid spends on the formation being treated. These precipitates include iron hydroxide and iron sulfide. In addition, chelating agents are used as components in many scale removal/prevention formulations. Two different types of chelating agents are in use: polycarboxylic acids (including polyaminopolycarboxylic acids) and phosphonates. Chelating formulations based on ethylenediaminetetraacetic acid (EDTA) have been used extensively to control iron precipitation and to remove scale. Formulations based on nitrilotriacetic acid (NTA) and diethylenetriaminepentaacetic acids (DTPA) also are in use. Each of these materials has problems: 1) EDTA has low solubility in hydrochloric acid and is not readily biodegradable in standard laboratory tests. 2) NTA is acid soluble and biodegradable, but has a lower stability constant for iron than EDTA (or DTPA) and is considered to be an animal carcinogen. This report describes the search for the universal or ideal chelating agent for use in oilfield services. The materials evaluated include hydroxyaminopolycarboxylic acids (HACA) such as hydroxyethylethylenediaminetriacetic acid (HEDTA) and hydroxyethyliminodiacetic acid (HEIDA) as well as other types of chelating agents.

A preclinical investigation of the saturation and dosimetry of 153Sm-DOTMP as a bone-seeking radiopharmaceutical.

INTRODUCTION The therapeutic potential of the bone-seeking radiopharmaceutical 153Sm-labeled 1,4,7,10-tetraazacyclododecanetetramethylenephosphonic acid (153Sm-DOTMP) was assessed by measuring its dosage-dependent skeletal uptake at two chelant-to-metal ratios and its source organ residence times at a chelant-to-metal ratio of 1.5:1. A similar agent, 153Sm-labeled ethylenediaminetetramethylenephosphonic acid (153Sm-EDTMP), has been reported to exhibit dosage-limiting skeletal saturation. METHODS Sm-DOTMP was prepared with tracer activity of 153Sm and sufficient stable, unenriched Sm to simulate different activities. Cohorts of seven 280-g Sprague-Dawley rats were administered the equivalent of 296, 592, 888, 1184 and 1480 MBq (8, 16, 24, 32 and 40 mCi) at a fixed chelant-to-metal ratio of 1.5:1 and euthanized 3 h after administration. Cohorts of three 128-g Sprague-Dawley rats were administered equivalent dosages of 10.4, 592 and 888 (0.28, 16 and 32 mCi) at a fixed chelant-to-metal ratio of 270:1 and euthanized 2 h after administration. A simulated activity of 1480 MBq (40 mCi) at a chelant-to-metal ratio of 1.5:1 was administered to cohorts of seven rats that were euthanized at 2, 4, 24 or 48 h postadministration. The heart, lungs, liver, spleen, kidneys, small intestine, large intestine, urinary bladder, muscle and a femur were excised, weighed and counted. The data were analyzed to determine skeletal uptake and source organ residence times. RESULTS No statistically significant skeletal saturation was observed up to human-equivalent dosages of 370 GBq (10 Ci) at a chelant-to-metal ratio of 1.5:1, but the skeletal uptake dropped by 40% over the range of dosages at a chelant-to-metal ratio of 270:1. At a chelant-to-metal ratio of 1.5:1, the preferred ratio, the skeletal uptake fraction in rats was 0.408 (95% confidence interval 0.396-0.419) with an effective half-life of 47.3 h (95% confidence interval 42.3-53.7; the physical half-life of 153Sm is 46.3 h). Extrapolating to an adult human model, 52.9 GBq (1.43 Ci) of 153Sm-DOTMP would deliver 40 Gy to the red marrow. CONCLUSION 153Sm-DOTMP has dosimetry equivalent to that of 153Sm-EDTMP at low dosages, yet with no skeletal saturation at higher administered activities.