Detecting Shale Discontinuity between Different Layers Using Waterflood Tomography

Abstract

AbstractThis paper presents a novel signal processing method to detect the existence and location of shale discontinuities between layers with distinct permeabilities by using only waterflood injection and production data. Continuing the work by Y. Lin, et. al (SPE-132699-PP), we use a new waterflood tomography concept to analyze cross-flow behavior among different layers and estimate the hydraulic transmissivity via tomography mapping. With designed injection rates, we estimate the response times at the producers by monitoring production rates. The response time represents the ‘cost’ for the fluid to travel between well-pairs and we can use it to model the virtual path through different layers. We consider the case of waterflooding in the presence of permeability contrast in different layers. The fluid in the low permeability layer tends to flow through the shale discontinuity to the higher permeability layer thus forming vertical `high permeability cross-flow channels between the wells. With the response time, we are able to identify these 3D high perm channels to estimate the location of shale discontinuities causing the cross-flow. To the best of our knowledge, we are the first to propose this waterflood tomography method. Without significantly affecting daily operation and without the cost associated with tracer testing and seismic tomography, our technique only involves applying scheduled changes to the injection rates and analyzing the relationship between these changes and those in production rates.To demonstrate the application, using a commercial simulator, we build a double layer reservoir model with different permeabilities. We test a line drive case with injectors and producers having perforations in both lower and upper layers. By applying our designed injection and shut-in schedule, we show our method can provide a very accurate estimate of shale discontinuity location by recording accurate response times between well-pairs.