Evaluating the connectivity of shale gas wells by new rare element tracers

Abstract

Three types of rare earth elements, Pr, Yb and Sm, in shale gas well and fracturing fluid, which showed a low content and are environmentally friendly and chemically stable, formed complexes with ethylenediamine tetra-acetic acid and di-picolinic acid, both of which were applied as tracers in the determination of the connectivity of shale gas wells. A case study was made in two shale gas wells (Jiaoye 66-Z1HF and Jiaoye 66-Z2HF) of the middle gas reservoir in the Jiaoye No. 66 extended platform well group in the Fuling shale gas field of SINOPEC. We first injected rare element tracer into the wells, and then evaluated the connectivity of the Jiaoye No. 66 extended platform after fracuring by monitoring whether there was rare element tracer in the tracer-injected wells and the flow-back fluid from adjacent wells, and finally discussed the feasibility of three-dimensional development of the lower, middle and upper gas layers of the Fuling shale gas field. The results of flow-back fluid monitoring showed that a high content of Sm tracer, which had been injected into well Jiaoye 66-Z2HF, was occasionally found in well Jiaoye 66-Z1HF, indicating that there might be a connection between the middle gas layers of the two wells. There is no abnormal Pr, Yb or Sm concentrations in the monitoring wells of the lower gas layers, indicating that they were not connected with the central gas layers. A high concentration of Sm tracer was detected in the mixed back-flow fluid samples of wells Jiaoye 5-S2 and Jiaoye 5-S3 in the upper gas layer, indicating that they were connected to the central gas layers. The present investigation has verified that rare element tracer technology is a facile and effective method for the connection determination between shale gas wells and has broad application prospects.

Keywords

• rare elements
• tracer
• shale gas well
• connectivity