Shale Gas: Nanometer-Scale Observations and Well Modelling

Abstract

Our studies of the underlying fundamental gas-recovery mechanisms from shale gas are motivated by expectations of the increasing role of shale gas in national energy portfolios worldwide. We use pore-scale analysis of reservoir shale samples to identify critical parameters to be employed in a gas-flow model used to evaluate wellproduction data. We exploit a number of 3D-imaging technologies to study the complexity of shale pore structure: from lowresolution X-ray computed tomography (CT) to focused ion beam and scanning electron microscopy (FIB/SEM). We observe that heterogeneity is present at all scales. The CT data show fractures, thin layers, and density heterogeneity. The nanometer-scale-resolution FIB/SEM images show that various mineral inclusions, clays, and organic matter are dispersed within a volume of few-hundred lm 3 . Samples from different regions differ sharply in the shape, size, and distribution of pores, solid grains, and the presence of organic matter. Although the samples have clearly distinguishable signatures related to the regions of origin, extremely low permeability is a common feature. This and other pore-scale observations suggest a bounded-stimulated-domain model of a horizontal well within fractured shale that accounts for both compression and adsorption gas storage. Using the method of integral relations, we obtain an analytical formula approximating the solution to the nonlinear pressure diffusion equation. This formula makes fast and simple evaluation of well production possible without resorting to complex computations. It defines a decline curve, which predicts two stages of production. During the early stage, the production rate declines with the reciprocal of the square root of time, whereas later, the rate declines exponentially. The model has been verified by successfully matching monthly production data from a number of shale-gas wells collected over several years of operation. Under appropriate conditions, scaling can collapse the data from multiple wells on a single type curve. Pore-scale image analysis and the mesoscale model suggest a dimensionless adsorption-storage factor (ASF) to characterize the relative contributions of compression and adsorption gas storage.

Water and Methane in Shale Rocks: Flow Pattern Effects on Fluid Transport and Pore Structure

“…Understanding these interactions and how they affect the fluid transport is crucial to design effective stimulation practices and optimal gas production strategies, as well as for reducing the environmental impact of shale gas. 3,5 Building on the results obtained by those scientists devoted to study the behaviour of fluids in narrow pores (i.e., the adsorption community), it is our goal to better understand the mechanism of fluid migration, in particular when two phases form, through shale formations using various modeling approaches.…”

An Analysis for the Influences of Fracture Network System on Multi-Stage Fractured Horizontal Well Productivity in Shale Gas Reservoirs

“…As Hill reported [8], approximately 30-60% of the gas occurs by adsorption mechanism. Based on the analysis of experiments, the majority of current research uses Langmuir's isotherm to describe the adsorbed gas [36][37][38][39]. Moreover, the theory is also adopted in many commercial simulators [40].…”

Molecular Dynamics Simulations of Adsorption of CH4 in Nanocone

“…China has shale gas resource of 3.16×10 13 m 3 and has the great potential for developing shale gas in the world [5,6]. Most of gas in coal seam is in adsorbed state, generally between 70% and 85% [7,8]. A significant part of the pores distributed in the shale is on the nanometer scale [9][10][11].…”