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Technical Paper: Evaluating Hydraulic Fracture Effectiveness in a Coal Seam Gas Reservoir From Surface Tiltmeter and Microseismic Monitoring

Society: SPE
Paper Number: 133063
Presentation Date: 2010
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Abstract

In developing new coalbed methane (CBM) or coal seam gas (CSG) fields or reservoirs, a good understanding of the potential impact of reservoir parameters is crucial in determining the success of hydraulic fracturing treatments. Estimating fracture geometry relative to the reservoir’s architecture is critical to understanding production variability. The Walloon Coal Measures, in the Surat Basin of Eastern Queensland, Australia, are a complex reservoir containing interbedded sandstone, siltstone, carbonaceous shale and coal seams. Initial attempts at hydraulic fracturing, in early pilot areas of the Surat Basin, yielded poor results; thus, when a hydraulic fracturing program was planned for this reservoir, it was decided to integrate diagnostics that would be useful in understanding past results as well as identifying future improvements.

Data is presented from two wells in the Walloon Sub Group (WSG) where tiltmeters and microseismic monitoring were used to evaluate fracture effectiveness relative to the reservoir architecture and to assist further design work. The treatments carried out in the studied wells were typical of CSG frac treatments used in other producing areas, incorporating stages of treated, gelled and crosslinked-gelled water with increasing concentrations of sand, up to six (6) lbm/gal. During the treatments, complex fractures were inferred based on analyses of data from both tiltmeter and microseismic monitoring methods. The collaborative data set for these wells also included a large amount of other analytical and diagnostic data. It was only possible to fully explain the treatment results through a combination of multiple diagnostics and an in-depth understanding of how the created fracture interacted with the complex reservoir and stress environment.

In this paper, we outline the steps used to plan the monitoring program and describe how geological data was integrated to better understand the results observed during the treatments. We describe each of six  stages performed across the two wells, and how the diagnostics did or did not support the overall conclusions as to the effectiveness of each stage. Finally, this paper presents a logical framework to evaluate and integrate these technologies for use in future CSG well stimulation.

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