Study on an Anti-adsorption Micromaterial Tracer System and Its Application in Fracturing Horizontal Wells of Coal Reservoirs

[Image: see text] The high adsorption capacity of coal reservoirs poses a challenge to the evaluation of productivity and output profiles for each segment of fractured horizontal wells using tracers. In this study, the microstructure of a coal sample from block B and its absorption character to a micromaterial tracer are analyzed first. Then, an anti-adsorption micromaterial tracer system which is suitable for block B is proposed by evaluating different types of complexing agents and extractant agents. The system comprises micromaterial tracers (200 ppb) + ethylenediaminetetraacetic acid tetrasodium (EDTA-4Na in short) (0.01%) + di(2-ethylhexyl) phosphate (HDEHP in short) (0.001%), and its anti-adsorption character of the system is analyzed. The concentration dynamics of micromaterial tracers are analyzed by the flowback fluid testing of one fracturing well and two adjacent wells. Then, a judging method for productivity and connectivity of each segment of horizontal wells is established. Moreover, the anti-adsorption micromaterial tracer system judgment method is employed to analyze the staged fracturing performance of horizontal well B1 in the coal reservoir of block B. Eight types of micromaterial tracers are utilized to label the fluid in each fracturing segment for assessing the connectivity between well B1 and adjacent wells B1-1 and B1-2. The results show that the anti-adsorption micromaterial tracer system exhibits minimal adsorption loss and can be well applied in segment monitoring in the horizontal fracturing well of coal reservoirs. The main productive segments of well B1 are #1, #4, and #8. Well B1 exhibits good connectivity with adjacent well B1-1 in segments #1, #4, #6, and #8. Conversely, all segments of well B1 exhibit poor connectivity with adjacent well B1-2. The results can provide a dependable reference for optimizing fracturing parameters, well spacing, and productivity evaluation in coal reservoirs. The results obtained in this study are consistent with the results obtained by using the four-dimensional (4D in short) image monitoring technology, which proves the good accuracy and reliability of the micromaterial tracer monitoring method.