Abstract

This invention relates a method and apparatus for studying the desorption of gases from coals using optical microscopy. Such desorption reveals the ways in which production of gas from coal occurs under various completion and production scenarios. It can also reveal the efficacy of various stimulation and enhancement methods. The invention discloses methods and apparatus that enable simulation of coalbed reservoirs in a laboratory, and teaches how correlating various analytical techniques with said microscopy can allow researchers to readily evaluate coalbed reservoir properties and production factors.

Introduction

Recent advances in laboratory simulations of coalbed methane (CBM) reservoirs allow for the examination and video capture of the coal-water interface during dewatering. Laboratory simulations of CBM reservoirs allow for the scientific investigation of reservoir properties. Sub-saturated coal samples are carefully prepared by means of a mass flow controller (which counts the number of methane molecules added to the cell) and over-pressurized by means of an air-driven water piston pump. In addition, reservoir properties and/or production factors may be varied in order to evaluate their relative effects. Once the sample cell has had adequate time to achieve equilibrium, a close focus telescope with CCD imager plane is used to capture the depressurization of the sample cell and desorption of methane from the coal surface. In addition to providing the first visual evidence of methane desorbing from coal, the ability to capture video microscopy of the depressurization of simulated reservoirs provides a new method for the examination of the effect of various reservoir parameters on dewatering.

Statement of Theory and Definitions

The study of desorption of gases from coals reveals the ways in which production of gas from coal occurs under various completion and production scenarios. It can also reveal the efficacy of various stimulation and enhancement methods.

Laboratory simulation of CBM reservoirs allows variation of pertinent reservoir parameters, such as temperature, pressure, and salinity. This provides a method for thorough experimentation and interpretation of the coal of interest. Reservoir parameters can then be independently examined and best practices for specific areas may be developed from the results.

Description and Application of Equipment and Procedures

The capture of video microscopy of the desorption of gases from coal requires two parts:

  1. a high-pressure sample cell with coal loaded to specific reservoir conditions (i.e. temperature, pressure, salinity) equipped with an optical window and

  2. a video microscopy camera capable of focusing through the sample cell's optical window onto the coal surface (Figure 1). (For additional information on the preparation of simulated CBM reservoirs see Laboratory Simulations of CBM Reservoirs; Patent #).

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