Rapid Analysis of Offset Well Pressure Response during Fracturing:Distinguishing between Poroelastic,Hydraulic and Frac-Hit Responses in Field Data Using Pattern Recognition

摘要

During fracturing,pressure responses are often observed in a nearby offset monitor well as hydraulic fractures propagate from the treatment well towards the monitor well.These pressure responses can be caused by,(a)purely poroelastic interactions between the treatment and monitor well fractures,(b)a combination of poroelastic interaction and hydraulic connection between the fractures(mixed response)or(c)massive direct frac-hits from the treatment into the monitor well fractures.In this work,we demonstrate an automated pattern recognition workflow to systematically identify and interpret the different types of pressure responses observed in field data from the Permian Basin.An automated pattern recognition workflow based on Python scripting has been developed that parses field offset well pressure data during fracturing from multiple wells,stage-by-stage,in each well.The script develops overlay-plots containing treatment and monitor well pressure for each stage,which can be stored in a directory of the user's choice(for future reference).The script then automatically determines the magnitude of pressure response as well as the type of pressure interference-“purely-poroelastic”,"mixed"[poroelastic + hydraulic] or"direct frac-hit”-and the output is automatically stored stage-by-stage in a user-friendly text delimited(“.txt”,".csv"or".xlsx”)format while the script executes.In addition,the script can also calculate the fracture azimuth based on relative distance between interacting stages and the magnitude of the observed pressure response.In case of a purely poroelastic response,pressure fall-off is observed in the monitor well as soon as the nearby treatment well is shut-in(Seth et al.,2019a).This is an important distinction between purely poroelastic responses and other types of pressure responses where a pressure increase is observed even after the nearby treatment well is shut-in.The magnitude of pressure response also varies with the type of pressure response.Typically,purely poroelastic pressure responses range between 1-100 psi(sometimes higher)depending upon the distance and overlap between the interacting fractures,whereas mixed pressure responses range between 10s-100s of psi.Direct frac-hits usually cause a massive increase in the offset monitor well pressure(100s-1000s of psi)and are relatively easy to spot visually as they disrupt the pressure response trend.It is crucial to correctly identify and interpret the type of pressure interference observed in field offset well pressure data before using this data for further analysis(such as fracture geometry estimation).This work details the different types of pressure responses typically observed in field data and provides guidelines on identifying and characterizing these responses correctly.In addition,the demonstrated automated workflow introduces a novel tool to systematically parse and characterize field offset well pressure data efficiently and calculate fracture azimuth based on magnitude of observed pressure response and distance between the interacting stages.