The options for acquiring microseismic data to evaluate hydraulic fracture treatments have expanded in recent years to include surface and near-surface monitoring. However, there has been an absence of detailed and comprehensive validation and comparison of the various monitoring techniques, leading to misconceptions and uncertainties concerning the different alternatives. Traditional downhole monitoring is constrained by the requirement for adequately located deep monitor wells, which limits application in exploration and appraisal and other areas without suitable monitor wells. Surface monitoring provides a means to gathering important microseismic data without the need for observation wells, although the validity of the results is sometimes questioned.

This paper presents detailed "side-by-side" comparisons of surface and near-surface monitoring techniques and provides guidelines for the application of the various monitoring options. This multi-year journey was undertaken by comparing several surface/near-surface data sets with their downhole counterparts in a series of concurrent surveys in US shale plays. These comparisons answer the following questions concerning sensitivity, attenuation, and location uncertainty of surface monitoring options:

  • How do the microseismic events detected and located at the surface or near-surface compare with those detected and located downhole?

  • What is the best surface or near-surface design and what parameters are key to optimizing it?

  • How does the processing and analysis of surface data compare with that of downhole data?

The paper includes a rare dataset from a field laboratory in the Fayetteville shale that was instrumented with a 4000 geophone surface microseismic array, a 5 Shallow Hole Grid, and traditional downhole microseismic arrays located in both vertical and horizontal observation wells. In addition, a 71-level geophone array was deployed from TD to surface in a vertical observation well. This multifaceted monitoring provided an unparalleled dataset to compare the various microseismic monitoring options.

The paper documents how and when the surface or near-surface technique provides a meaningful alternative to downhole monitoring both technically and economically, presents candidate selection criteria and provides a comprehensive comparison of the relative technical and economic merits of each monitoring option.

Keywords:
reservoir characterization, noise level, detection, monitoring, upstream oil & gas, logistics, geometry, microseismic monitoring, hydraulic fracturing, microseismic event
Subjects:
Hydraulic Fracturing, Reservoir Characterization, Seismic processing and interpretation
Copyright 2012, Society of Petroleum Engineers
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