Fracture Diagnostics Research at the GRI/DOE Multi-Site Project: Overview of the Concept and Results
Authors: Peterson R.E. , Wolhart S.L. , Frohne K.H. , Branagan P.T. , Warpinski N.R. , Wright T.B. 
Published: December 2007

The Multi-Site Hydraulic Fracture Diagnostic Project was initiated to develop independent diagnostic technologies and methodologies that will result in increased accuracy in measuring hydraulic fracture dimensions. Through a series of field experiments, the project has provided key insights into the time-dependent growth and total dimensions of hydraulic fractures. Wire line-retrievable and cemented-in triaxial accelerometer arrays provide the basis for plan and profile maps of microseismic events associated with the hydraulic fracture. A vertical inclinometer array provides data on the earth's mechanical response to fracture opening and closure.

A directionally drilled wellbore remotely intersected the hydraulic fracture interval, verified the accuracy of microseismically imaged hydraulic fracture azimuth, and provided ground-truth observations on the far-field character of hydraulic fractures. Although eleven far-field hydraulic fractures were observed, it cannot be definitively determined if they are the result of multiple injections. Collectively, data resulting from M-Site research indicate that hydraulic fracture wings are not always symmetrical, rapidly attain their full length extent with only limited fracture height growth, and that hydraulic fractures propagated only with fluid retain their width for a long time period. Although these results apply to the zones being tested at the M-Site, they should also transfer to other zones with comparable thickness and stress contrast.

Introduction

Project Objective and Initiation Logic. The jointly funded Gas Research Institute (GM) and U.S. Department of Energy (DOE) Multi-Site (M-Site) Project is focused on performing field-scale experiments and gathering high-quality, independent diagnostic data that will result in increased accuracy in measuring hydraulic fracture dimensions. The ultimate goal of the project is to develop the hardware and methodology necessary to establish a microseismic-based system that can be used as the foundation for a commercial hydraulic fracture mapping capability.

Several inter-related technology- and economics-based reasons prompted GRI and DOE to initiate a project of this magnitude. Each organization has a long history of supporting research directed toward determining the size and shape of hydraulic fractures. These research efforts include the development of real-time models for history matching of fracture treatment pressures, the collection and analysis of rock and reservoir properties that control fracture growth (e.g., in-situ stresses and rock properties), the estimation of fracture length and conductivity based on production, and the development of various fracture diagnostics for azimuth and height measurement. However, throughout all of these efforts, no reliable tool or technique was developed for determining the total fracture extent, primarily because of the difficulty in estimating fracture length.

Fracture modeling is currently the most common method for estimating hydraulic fracture extent. However, without a definitive method for imaging or mapping the hydraulic fracture extent there is no field-scale ground-truth measurement with which to compare fracture model results. Lacking an accurate measurement of fracture dimensions, modelers and stimulation treatment designers are likely to continue to have diverse opinions regarding the importance of various fracturing mechanisms (e.g., tip effects, complex fracturing and height growth) and controlling parameters (e.g., closure stress measurements and in-situ modulus).

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