The Mississippian Barnett Shale reservoirs have opened a new era for US gas production. Many reservoir characterization efforts have been made and completion practices established to help understand the Barnett Shale reservoirs. The borehole image interpretation, drilling-induced fractures and conductive/healed fractures, reveals stress regime orientation, fracture morphology and their orientations. The interpreted results guide the design of horizontal wells to control hydraulic fracture directions and intensities. Conventional logs and cores have been used to classify lithofacies and estimate petrophysical and geomechanical properties for well positioning and reserve calculations. The seismic survey is not only interpreted for structure horizons and faults, but also analyzed for 3D property evaluations such as lithofacies distribution, discrete fracture network, and stress field. On the operation side, longer horizontal wells are drilled and massive multistage, multicluster hydraulic fracturing treatments (HFT) are executed. Various well placement and HFT schemes are performed. The microseismic (MS) has played an important role in understanding the estimation of hydraulic fracturing stimulated reservoir volume (ESV) and fracture intensities.
In spite of this tremendous effort and progress, a systematic methodology appears lacking in the literature to integrate the variety of information and obtain accurate reservoir characterizations. In this paper, we present an integration workflow that incorporates seismic interpretations and attributes, borehole image and log interpretations, core analysis, HFT, and microseimic data to construct reservoir models and discrete fracture networks that are then upscaled to dual-porosity reservoir models for numerical simulation. The application of this workflow in field studies has revealed important observations and provided better understanding of the reservoirs.
This integration workflow demonstrates an effective methodology for capturing the essential characteristics of Barnett Shale gas reservoirs, and offers a quantitative means and platform for optimizing shale gas production.
Introduction
Driven by gas consumption demand and rising oil and gas prices in the past several years, Barnett Shale gas production has gained momentum. The characteristics of the Barnett Shale reservoir can be typically described as extremely low permeability (100-600 nano-Darcys), low porosity (2-6%), and moderate gas adsorption (gas content 50-150 scf/ton). The general Barnett Shale reservoir deposition settings, lithofacies, natural fracture characterization, and production evaluation can be found in Louks et al. (2007), Gale et al. (2007), and Frantz et al. (2005). In order to achieve economical production and enhance productivity, a large number of horizontal wells have been drilled and massive multistage HFT jobs have been performed. Due to the complex nature of the Barnett reservoirs which is vastly different than that of conventional or other types of unconventional reservoirs, it is difficult to obtain a clear understanding and an accurate description of the reservoir. To quickly acquire knowledge and guide imminent placement (well spacing and pattern) designs, various well spacing pilots (e.g., 500 ft, 1,000 ft, and 1,500 ft, etc.) were drilled and various hydraulic fracturing operation schemes such as "zipper-frac" and "simul-frac" have been invented and tested (Waters et al., 2009).
