Nuclear Well Logging Organic Carbon Estimation
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Solution Overview
Problem
Current well logging systems face challenges in accurately determining the organic carbon content of geological formations, particularly in distinguishing between inorganic and organic carbon, which is crucial for identifying hydrocarbon source rocks and assessing hydrocarbon potential.
Innovation Solution
A method and apparatus that utilize nuclear well logging techniques to measure and analyze gamma radiation from earth formations, estimating organic carbon content by differentiating between inorganic carbon associated with known minerals and organic carbon present in pore spaces, using a Th/U ratio to characterize organic carbon as a source rock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gamma ray spectroscopy is used to measure total carbon content, then carbon quantification is achieved, but differentiation between inorganic and organic carbon is not possible
Solution Approach 1:
The patent segments the carbon measurement problem into two distinct components: inorganic carbon (from carbonate minerals) and organic carbon (from hydrocarbons and source rocks). It measures total carbon via gamma ray spectroscopy, then separately quantifies inorganic carbon using mineralogical data from the same spectroscopy, and finally calculates organic carbon by subtraction. This segmentation allows precise organic carbon estimation while managing complexity through systematic decomposition of the measurement problem.
Solution Approach 2:
The patent uses an intermediary approach by introducing mineralogical parameters (carbonate mineral content) as a mediator between the total carbon measurement and the organic carbon calculation. The gamma ray spectroscopy provides both total carbon and mineralogical information simultaneously, with the mineral content serving as an intermediary that enables separation of inorganic and organic carbon components through mathematical relationship.
2Measurement precision
If neutron bombardment is used to excite gamma rays, then elemental identification is achieved, but measurement time is increased
Solution Approach 1:
The patent employs periodic action by using pulsed neutron sources that bombard the formation in cyclic intervals. The neutron source is activated for brief periods to generate gamma rays, then allowed to decay, creating a periodic measurement cycle. This enables elemental identification through gamma ray spectroscopy while controlling measurement time through the pulsing duration and frequency, balancing data quality with time efficiency.
3Adaptability or versatility
If multiple logging tools are used to measure different formation parameters, then comprehensive formation evaluation is achieved, but device complexity increases
Solution Approach 1:
The patent merges multiple measurement capabilities into a single integrated logging tool that combines gamma ray spectroscopy for elemental analysis, neutron porosity measurement, and formation evaluation functions. By consolidating these previously separate tools into one unified system, it achieves comprehensive formation evaluation (versatility) while reducing operational complexity through integrated data acquisition and processing.
Solution Approach 2:
The patent creates a universal logging tool that performs multiple functions: measuring total carbon content, identifying carbonate minerals, determining porosity, and evaluating hydrocarbon potential. This multi-functional approach allows a single tool to replace multiple specialized tools, enhancing adaptability across different formation types and evaluation objectives while managing system complexity through unified design.
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 precise estimation of organic carbon content, including hydrocarbons, bitumen, coal, and biogenic matter, facilitating better decision-making in hydrocarbon exploration by accurately identifying source rocks and their potential.
Implementation Method 1
These systems measure gamma rays in the formation caused by bursts of neutrons into the formation by a neutron source carried by the tool and pulsed at a preselected interval
Implementation Method 2
Different elements in the formation may thus be identified from characteristic gamma ray energy levels released as a result of this neutron bombardment
Implementation Method 3
reliance is made upon the physical phenomenon that the energies of gamma rays given off by nuclei resulting from natural radioactive decay or induced nuclear radiation are indicative of the presence of certain elements within the formation
Implementation Method 4
when high-energy neutrons on the order of 14.2 MeV collide with the nuclei of the formation elements
Implementation Method 5
measure gamma rays in the formation caused by bursts of neutrons into the formation by a neutron source carried by the tool and pulsed at a preselected interval
Implementation Method 6
Well logging systems for measuring neutron absorption in a formation use a pulsed neutron source providing bursts of very fast, high-energy neutrons
Implementation Method 7
As the neutrons are slowed to the thermal state, they may be captured by atoms in the surrounding matter. Atoms capturing such neutrons are also caused to be in an excited state, and after a short time gamma rays are emitted
Implementation Method 8
Neutrons leaving the pulsed source interact with the surrounding environment and are slowed down. Such collisions may impart sufficient energy to these atoms to leave them in an excited state, from which after a short time gamma rays are emitted
Implementation Method 9
Such emitted gamma rays are labeled inelastic gamma rays
Implementation Method 10
it is frequently useful to obtain data regarding the time spectral distributions of the occurrence of the gamma rays. Such data can yield extremely valuable information about the formation, such as identification of lithologies that are potentially-hydrocarbon producing
Data Source
AI summary
Elemental analysis of an earth formation is obtained using measurements from a gamma ray logging tool. From the elemental analysis, an estimate of the Calcium, Magnesium and Carbon content of the formation is determined. The amount of organic carbon in the formation is estimated from the total Carbon content and the inorganic carbon associated with minerals in the formation. An indication of source rock may be obtained from the Th/U ratio.