Evaluating Hydraulic Fracture Effectiveness in a Coal Seam Gas Reservoir from Surface Tiltmeter and Microseismic Monitoring

Abstract

In developing new coalbed methane (CBM) or coal seam gas (CSG) fields or reservoirs, the effect of many parameters are important in understanding the success or potential areas for improvement of hydraulic fracturing treatments. Estimating fracture geometry relative to the reservoir 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 where 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 a group of diagnostics that would be useful in understanding past results as well as deriving 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 analyses and diagnostic data. It was only possible to fully explain the treatment results through the 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 (6) 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.2 SPE 133063 growth that would limit fracture extension or might lead to wellbore failures following hydraulic fracturing (Jeffrey et al. when a program to incorporate hydraulic fracturing was considered, it was decided that an integrated diagnostics program would be essential in understanding the fracture geometry and overall stress environment in order to improve treatment designs and to help understand past treatment results. Ridgewood Frac Pilot AreaThe area of investigation, the Ridgewood pilot (see Figure 2), was drilled on a localized structural high that appears to be a southwestern continuation of the Kogan Anticline. This area was investigated to determine if enhanced natural fracturing and associated higher permeability might exist east of the...

A Validation Assessment of Microseismic Monitoring

“…Fault identification is discussed later in the paper. A study in a coalbed methane reservoir in the Surat basin of Queensland (Johnson et al 2010) compared microseismic azimuths to those derived from surface tiltmeters. Although the fractures were complex (both horizontal and vertical components), the general azimuth from the two technologies reasonably agrees for several of the tests.…”

Stimulation of Unconventional Reservoirs using Graded Proppant Injection

“…Where ␤ is dimensionless aspect ratio (9) Dimensionless aspect ratio ␤ values calculated by Eq. 9 are presented in Table 2 for all three particle placement tests (Fig.…”

“…Hydraulic fracturing of coal seams is mainly a process that interconnects the natural fracture network to a wellbore (Holditch et al, 1988;Xu et al, 2013a;Xu et al, 2013b). However, based on highly instrumented experiments in coals, varying dimensions of the created hydraulic fractures unlikely would result in accepting the main body of proppant introduced into fractures at latter stages of the treatment to maintain hydraulic fracture conductivity (Johnson et al, 2010a;Johnson et al, 2010b;Scott et al, 2010). Any process that can maintain post-frac conductivity throughout the initial, complex and pressure dependent created fractures, natural fractures and cleat networks surrounding the main hydraulic fracture could significantly increase the efficiency of hydraulic fracturing in CBM reservoirs.…”

Lessons Learned from Engineering Analysis of Fracture Injection Tests from Different CBM Reservoirs

“…The complexity and the effects of hydraulic fracture design parameters like injection rate, fluid viscosity, proppants used, etc, can be simulated with unconventional fracture models ( Xiaowei et al 2011). The application of the microseismic technique has also been tried on CBM fracturing in Australia (Johnson et al 2010).…”