Estimating Adsorbed Gas Volume via NMR and Dielectric Logs

Solution Overview

Problem

Current methods for estimating adsorbed gas volume in Coal Seam Gas (CSG) or Coal Bed Methane (CBM) are time-consuming and yield inaccurate results due to lost gas during core sampling, requiring up to six months for accurate measurement.

Innovation Solution

Combining Nuclear Magnetic Resonance (NMR) data correction with dielectric permittivity measurements to estimate formation porosity and water-filled porosity, allowing for the calculation of gas volume using an equation of state, thereby providing a timely and more accurate assessment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If core sampling method is used to estimate adsorbed gas volume, then measurement accuracy is improved, but time required increases significantly (up to six months)

Engineering Contradiction:

Improvegas volume measurement accuracyVSAvoidtime required for measurement

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent replaces the mechanical core sampling and laboratory analysis system with an in-situ NMR logging system that measures gas volume directly in the formation. The NMR tool uses magnetic fields and radio frequency pulses to detect hydrogen nuclei in adsorbed gas, eliminating the need for physical core retrieval and lengthy laboratory desorption measurements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The NMR measurement is performed in-situ while the formation is still in its natural state, before any gas can be lost. The measurement is conducted immediately during the logging operation, eliminating the delay between core sampling and measurement that causes gas loss in traditional methods.

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If core sampling method is used to estimate adsorbed gas volume, then measurement accuracy is improved, but cost increases due to lost gas and extended measurement period

Engineering Contradiction:

Improvegas volume measurement accuracyVSAvoidcost associated with lost gas and extended measurement

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

The patent replaces the mechanical core sampling and laboratory analysis system with an in-situ NMR logging system that measures gas volume directly in the formation. The NMR tool uses magnetic fields and radio frequency pulses to detect hydrogen nuclei in adsorbed gas, eliminating the need for physical core retrieval and lengthy laboratory desorption measurements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Quantity of substance

If traditional core sampling and desorption measurement is used, then gas volume can be measured, but gas loss during sampling reduces measurement accuracy

Engineering Contradiction:

Improvegas volume measurementVSAvoidgas lost during core sampling

Core Design Contradiction:

Quantity of substanceVSLoss of substance

Solution Approach 1:

The patent replaces the mechanical core sampling and laboratory analysis system with an in-situ NMR logging system that measures gas volume directly in the formation. The NMR tool uses magnetic fields and radio frequency pulses to detect hydrogen nuclei in adsorbed gas, eliminating the need for physical core retrieval and lengthy laboratory desorption measurements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enables rapid estimation of adsorbed gas volume, reducing the time and cost associated with traditional core sampling methods while improving the accuracy of in-situ gas volume estimates.

Implementation Method 1

Nuclear Magnetic Resonance (NMR) tools used for well-logging or downhole fluid characterization measure the response of nuclear spins in formation fluids to applied magnetic fields

Methodology Applied

Scientific EffectNuclear Magnetic Resonance: Magnetism

Implementation Method 2

A dielectric permittivity tool measures the dielectric permittivity of a material. The dielectric permittivity is related to the ability of electric dipoles in a material to form and align themselves with an alternating electric field

Methodology Applied

Scientific EffectDielectric permittivity: Dielectric

Data Source

PatentUS9753176B2Estimating adsorbed gas volume from NMR and dielectric logs

Publication Date: 2017.09.05 SCHLUMBERGER TECH CORP

AI summary

Adsorbed gas in a formation may be estimated. Nuclear magnetic resonance (NMR) data for a subsurface geological formation is obtained, and at least a portion of the NMR data is corrected to produce corrected NMR data. A NMR-based estimate of formation porosity is determined using the corrected NMR data. Dielectric permittivity data for the subsurface geological formation is obtained, and a dielectric permittivity-based estimate of the formation water-filled porosity is determined using the dielectric permittivity data. A gas volume is determined using the determined NMR-based estimate of the formation porosity and the determined dielectric permittivity-based estimate of the formation water-filled porosity. The gas volume may be determined by subtracting the determined dielectric permittivity-based estimate of the formation water-filled porosity from the determined NMR-based estimate of the formation porosity. The gas volume per unit volume of the formation may be determined using an equation of state.