HYDRAULIC FRACTURING EVALUATION UTILIZING SINGLE-WELLS-WAVE IMAGING: IMPROVED PROCESSING METHOD AND FIELD EXAMPLES

摘要

produces artificial fractures and creates oil and gas seepage channels. It has now grown into an indispensable technology for oil and gas exploration and development, which leads to the evaluation of hydraulic fracturing effects, ie the development of hydraulic fractures, as well as the connection with natural fractures, becoming necessary. In this paper, we introduce the single-well S-wave imaging method, commonly used to recognize reflectors such as natural fractures and caves outside the well, to do the hydraulic fracturing evaluation. The specific implementation is to acquire array acoustic logging data once in the open hole before fracturing, and then to measure again in the cased hole after fracturing. The difference between the two imaging results reflects the development of hydraulic fractures. However, the normal processing steps of S-wave imaging cannot meet the demand, due to the complex hydraulic fracture network and the interaction with natural fractures. For this purpose, five types of noises that affect the signal-to-noise ratio of S-wave imaging are concluded: low-frequency and high-frequency noise, multiple wave, formation boundary wave, and random noise. A set of improved processing methods for suppressing noise in S-wave imaging are further developed.Field applications demonstrate the improved processing methods that noise is suppressed effectively and imaging of real reflectors becomes clear. By comparing migration image before and after hydraulic fracturing, artificial fractures growing along the borehole wall can be observed. More importantly, we can see the extension of artificial fractures radially into the formation as far as 25 meters and even the connection with natural fractures. It should be pointed out that S-wave imaging cannot directly identify main hydraulic fractures almost vertical to the well, but can identify the numerous secondary hydraulic fractures almost parallel to the well, which always accompany the main fractures.As we all know, microseismic monitoring is a widely used technology to image hydraulic fractures. So in this paper, we attempts to combine S-wave imaging of high resolution but short detection distance with microseismic imaging of low resolution but far detection distance to evaluate hydraulic fracturing. In an actual well, the corresponding depth positions and directions of natural fractures are determined by S-wave imaging before hydraulic fracturing, and microseismic events representing hydraulic fractures are recorded during hydraulic fracturing period. Comparing S-wave imaging and microseismic imaging, it is found that the layer that microseismic events appearing most frequently is also the layer with numerous natural fractures, and the extension azimuths of both artificial fractures and natural fractures are consistent, which indicates that it is practicable to use S-wave imaging and microseismic imaging to jointly evaluate hydraulic fracturing.