Importance of borehole deviation surveys for monitoring of hydraulic fracturing treatments

Abstract

A B S T R A C TDuring seismic monitoring of hydraulic fracturing treatment, it is very common to ignore the deviations of the monitoring or treatment wells from their assumed positions. For example, a well is assumed to be perfectly vertical, but in fact, it deviates from verticality. This can lead to significant errors in the observed azimuth and other parameters of the monitored fracture-system geometry derived from microseismic event locations. For common hydraulic fracturing geometries, a 2 • deviation uncertainty on the positions of the monitoring or treatment well survey can cause a more than 20 • uncertainty of the inverted fracture azimuths. Furthermore, if the positions of both the injection point and the receiver array are not known accurately and the velocity model is adjusted to locate perforations on the assumed positions, several-millisecond discrepancies between measured and modeled SH-P traveltime differences may appear along the receiver array. These traveltime discrepancies may then be misinterpreted as an effect of anisotropy, and the use of such anisotropic model may lead to the mislocation of the detected fracture system. The uncertainty of the relative positions between the monitoring and treatment wells can have a cumulative, nonlinear effect on inverted fracture parameters. We show that incorporation of borehole deviation surveys allows reasonably accurate positioning of the microseismic events. In this study, we concentrate on the effects of horizontal uncertainties of receiver and perforation positions. Understanding them is sufficient for treatment of vertical wells, and also necessary for horizontal wells.

Challenges for microseismic monitoring

“…An alternative explanation of stage-to-stage changes in velocity model calibration was offered by Bulant et al (2007) who pointed out that errors in deviation surveys of both treatment and monitoring boreholes may cause significant and systematic changes in velocity model calibration (resulting in systematic bias in locations of microseismic events, as explained above). They show that VTI parameters of up to 20% (i.e.…”

Understanding acquisition and processing error in microseismic data: An example from Pouce Coupe Field, Canada

“…Failure to account for uncertainty and the limitations of a survey can lead to overinterpretation or misinterpretation of results (Bulant et al . ). Velocity model building has a significant effect upon estimated event locations and errors (Grechka and Yaskevich ; Grechka and Heigl ).…”

Microseismic Imaging of Hydraulically Induced-Fractures in Gas Reservoirs: A Case Study in Barnett Shale Gas Reservoir, Texas, USA

“…Furthermore, Reference [12] indicated that the prior knowledge of velocity structure can optimize the downhole geophone configuration within the available well geometry to provide a better location image. For accurate definition to the geophone placement and orientation in a vertical monitoring well, surveys including the deployment of a coil-tubing string charge in a nearby borehole are important [13]. It is a common practice in hydraulic fracturing jobs to use offset wells to install the microseismic monitoring array, but the treatment well can also be utilized for this purpose [14] with notable increase in the background noise resulting from sensors position close to the injection spot.…”