What are the key petrophysical parameters and workflows for characterizing unconventional gas resources?

1 Porosity and permeability

Porosity and permeability are the most fundamental petrophysical parameters that measure the storage and flow capacity of a reservoir. However, unconventional gas resources have very low porosity and permeability, often in the nanodarcy range, which makes them difficult to measure and analyze. To estimate porosity and permeability, you need to use advanced logging and core analysis techniques, such as nuclear magnetic resonance, mercury injection capillary pressure, and digital rock physics. You also need to account for the effects of stress, fractures, clay content, organic matter, and gas adsorption on these parameters.

2 Gas-in-place and recovery factor

Gas-in-place (GIP) and recovery factor (RF) are the key parameters that determine the economic potential of an unconventional gas resource. GIP is the amount of gas that is initially present in the reservoir, while RF is the fraction of GIP that can be produced. To estimate GIP and RF, you need to use different methods than those used for conventional reservoirs, such as the volumetric method, the modified material balance method, the decline curve analysis method, and the simulation method. You also need to consider the factors that affect GIP and RF, such as pressure, temperature, gas composition, rock properties, fracture properties, and completion and stimulation techniques.

3 Mineralogy and geochemistry

Mineralogy and geochemistry are the parameters that describe the composition and quality of the reservoir rock and the organic matter. Mineralogy and geochemistry affect the petrophysical properties, the gas generation and storage mechanisms, and the completion and stimulation performance of unconventional gas resources. To measure mineralogy and geochemistry, you need to use various logging and laboratory techniques, such as X-ray diffraction, X-ray fluorescence, pyrolysis, and gas chromatography. You also need to interpret the data using appropriate models and correlations, such as the TOC (total organic carbon) model, the kerogen type model, and the vitrinite reflectance model.

4 Fractures and natural fractures

Fractures and natural fractures are the parameters that describe the geometry and distribution of the induced and pre-existing cracks in the reservoir rock. Fractures and natural fractures are essential for enhancing the permeability and productivity of unconventional gas resources, as they create pathways for gas flow and storage. To characterize fractures and natural fractures, you need to use various logging and imaging techniques, such as acoustic, electrical, and microseismic logging. You also need to analyze the data using appropriate methods and tools, such as fracture orientation, fracture density, fracture aperture, fracture conductivity, and fracture network modeling.

5 Completion and stimulation

Completion and stimulation are the parameters that describe the design and execution of the wellbore and the hydraulic fracturing operations. Completion and stimulation are critical for optimizing the performance and recovery of unconventional gas resources, as they affect the contact area, the conductivity, and the pressure of the reservoir. To evaluate completion and stimulation, you need to use various data sources and techniques, such as well logs, production data, pressure data, tracer data, and microseismic data. You also need to apply appropriate models and software, such as fracture propagation models, reservoir simulation models, and production forecasting models.

6 Petrophysical integration

Petrophysical integration is the workflow that combines and synthesizes all the petrophysical parameters and data from different sources and scales. Petrophysical integration is necessary for building a comprehensive and reliable characterization of unconventional gas resources, as it enables the identification of sweet spots, the estimation of reserves, the optimization of development plans, and the evaluation of uncertainties. To perform petrophysical integration, you need to use a multidisciplinary approach and a systematic process, such as data acquisition, data quality control, data analysis, data integration, data visualization, and data interpretation.

7 Here’s what else to consider

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