Rayleigh Frequency Shift Distributed Strain Sensing (RFS-DSS) has been proven to be an insightful tool for investigating effective fracture geometry, production profiles, and drainage reservoir volume during stable production and well interference test. Recently, Hydraulic Fracturing Test Site1 Phase III (HFTS 1-III) in Eagle Ford has extended the application of this technique to monitoring strain responses in an adjacent well during preloading a parent well. The dataset shows similar patterns with the data acquired during stable production and shut-in periods. This study, for the first time, aims to analyze the acquired data and intents to relate measured strain responses to effective fracture geometry and sweep efficiency during preload.
In HFTS 1-III, a horizontal monitoring well has been drilled to monitor preload of a parent well and subsequent fracturing and production activities. Water was injected into the parent well for 24 hours to build up pressure. The monitoring well, about 225 ft to 250 ft away, acquired strain change data during the preload period and 6 hours after preload. The data has been pre-processed and visualized to identify the fiber slippage issue. The strain signals are interpolated according to the chosen slippage criteria to further process the data and remove the slippage effect. Location of perforation clusters from adjacent wells are projected to the monitoring well. Perforation locations are analyzed and correlated to positive peaks of strain responses.
The post-processed strain signals show stronger strain responses with obvious peaks and less small, scattered peaks. The strain peaks are statistically summarized, and the strain peak distributions are analyzed and correlated well with the existing perforation clusters projected onto the monitoring well. Positive peaks of strain responses have only been identified along the monitoring well where the vertical distance between the parent well and the monitoring well is less than 45 ft and the total distance between the parent well and the monitoring well is less than 260 ft, which may imply the magnitude of effective fracture geometry.
This study, for the first time, analyzes strain responses in the monitoring well during preload, highlights the value of the acquired dataset, and advances our understanding of field observations. In addition, we also demonstrate the potential to obtain effective fracture geometry by further analyzing the dataset.
