Continuous Oil Density Log Determination via C/O and Porosity Logs
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Solution Overview
Problem
Existing carbon-oxygen (C/O) techniques assume a constant oil density value, leading to errors and uncertainties in oil saturation determinations for hydrocarbon reservoirs.
Innovation Solution
A method is developed to determine a continuous oil density log by combining carbon/oxygen (C/O) logs with water saturation logs and porosity logs, using carbon and oxygen density values associated with reservoir rock and pore fluids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a constant oil density value is assumed in C/O techniques, then the measurement process is simplified, but the accuracy of oil saturation determination deteriorates
Solution Approach 1:
The patent transforms the static assumption of constant oil density into a dynamic approach by determining continuous oil density values at multiple depths along the wellbore. The oil density is calculated as a function of depth using the formula: ρo(z) = (Yc/Yo) × (1-φ) × ρo,rock + φ × Sw(z) × ρo,water - (1-φ) × ρo,rock, where density values vary with depth-based parameters Yc/Yo and Sw(z).
Solution Approach 2:
The patent changes the parameter approach by transitioning from a single constant density value to multiple depth-dependent density values. By incorporating depth-varying parameters (carbon yield ratio Yc/Yo and water saturation Sw at different depths), the oil density ρo becomes a variable parameter that adapts to local reservoir conditions at each depth interval.
2Ease of operation
If constant oil density is used in C/O logging, then operational simplicity is maintained, but oil saturation monitoring accuracy deteriorates
Solution Approach 1:
The patent performs preliminary determination of oil density as a continuous function of depth before conducting oil saturation monitoring. By pre-calculating ρo(z) using available C/O log data and water saturation information, the method prepares accurate density values that can then be directly applied to saturation calculations, improving monitoring accuracy without adding operational complexity during the monitoring phase.
Solution Approach 2:
The patent introduces oil density as an intermediary parameter that mediates between C/O log measurements and oil saturation determination. By first determining continuous oil density values from C/O ratios and then using these density values to calculate oil saturation, the method creates a two-step process that improves overall accuracy while maintaining operational simplicity through systematic data processing.
3Device complexity
If a single oil density value is assumed, then data processing is simplified, but uncertainties in petrophysical parameters increase
Solution Approach 1:
The patent segments the reservoir into multiple depth intervals, determining a separate oil density value for each interval. By dividing the continuous wellbore into discrete depth segments and calculating ρo(z) for each segment based on local C/O ratios and water saturation values, the method transforms a single uncertain value into multiple localized accurate values, reducing overall uncertainties in petrophysical parameters.
Solution Approach 2:
The patent adds the depth dimension to oil density determination, transforming the problem from determining a single scalar density value to determining a continuous density function ρo(z) across the vertical dimension of the wellbore. This dimensional expansion allows the method to capture spatial variations in oil density and reduce uncertainties by considering depth-dependent reservoir heterogeneity.
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 provides accurate and representative in-situ continuous oil density logs, reducing uncertainties and improving the accuracy of oil saturation monitoring, which is crucial for operational decision-making and reservoir development.
Implementation Method 1
conducting a pulsed neutron (PN) logging operation in the well to generate a carbon/oxygen (C/O) log for the well
Implementation Method 2
Carbon/oxygen (C/O) logging may be used for reservoir saturation monitoring and may show a particular sensitivity to changes in oil properties due to changes in the carbon content of the molecular structure of oil
Data Source
AI summary
A determination of a continuous oil density log for a hydrocarbon reservoir accessible via a well drilling into the formation having the reservoir. The logging operations may be conducted in the well to generate a carbon-oxygen ratio (C/O) log, a water saturation log, and a porosity log. A continuous oil density log may be determined using the C/O log, the water saturation log, the porosity log, and carbon and oxygen density values. The continuous oil density log may be used in further characterization and development of the hydrocarbon reservoir.