Asphaltene Evaluation Using NMR Temperature Pressure Cycling
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Solution Overview
Problem
Current methods for determining asphaltene content in crude oil, such as SARA analysis, are time-consuming and not suitable for rapid deployment in downhole or surface configurations, necessitating a more efficient technique for quantifying asphaltene fractions in hydrocarbon-bearing rock samples.
Innovation Solution
A method involving NMR measurements before and after temperature and/or pressure changes across the asphaltene precipitation onset condition is used to evaluate asphaltene content, utilizing downhole or surface NMR tools to compare diffusion-relaxation measurements and detect significant asphaltene presence through signal shifts indicative of irreversible behavior on rock surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SARA analysis is used to determine asphaltene content, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent replaces the mechanical/chemical SARA analysis system with an NMR (nuclear magnetic resonance) measurement system. The NMR tool measures diffusion and relaxation properties of fluids in the rock sample, and asphaltene content is determined by comparing NMR measurements taken before and after temperature/pressure cycling, eliminating the need for time-consuming chemical separation and analysis
Solution Approach 2:
The patent changes the physical parameters (temperature and/or pressure) of the rock sample to induce asphaltene precipitation. By cycling temperature and/or pressure across the asphaltene precipitation onset condition, the method creates measurable changes in NMR signal properties that correlate with asphaltene content, enabling rapid quantitative assessment
2Ease of operation
If downhole NMR measurement is performed, then ease of operation is improved, but measurement precision may worsen due to harsh conditions
Solution Approach 1:
The patent performs preliminary NMR measurements downhole at reservoir conditions before the rock sample is brought to surface. This captures the initial state of fluids in-situ. The same sample then undergoes temperature/pressure cycling and subsequent NMR measurements, allowing comparison that reveals asphaltene content while preserving the benefits of both downhole and laboratory measurements
Solution Approach 2:
The patent adds the dimension of temperature/pressure cycling to the NMR measurement process. By measuring NMR properties under multiple thermal and pressure states, the method enhances signal resolution and enables differentiation of fluid components, particularly asphaltenes, that would be difficult to distinguish under single static conditions
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 allows for a rapid and accurate estimation of asphaltene content, improving signal resolution and enabling in-situ evaluation of hydrocarbon-bearing rock samples, calibrated with SARA analysis for precise results.
Implementation Method 1
making a first NMR measurement representative of the hydrocarbon-bearing rock sample
Implementation Method 2
The first and second NMR measurements are diffusion-relaxation NMR measurements, such as Diffusion-T1 or Diffusion-T2 measurements
Implementation Method 3
lowering temperature and/or pressure of the hydrocarbon-bearing rock sample below an expected asphaltene precipitation onset condition
Implementation Method 4
The expected asphaltene precipitation onset condition is the critical point for asphaltene flocculation-dissolution on the asphaltene-precipitation envelope
Data Source
AI summary
Asphaltene content and its spatial distribution in a reservoir containing crude oil is an important factor in determining the potential for formation damage and pipeline impairment, as well as planning for processing and refining of the oil. Exemplary uses include: reservoir modeling, development and depletion planning, pressure maintenance, and surface facilities management. A convenient method has been developed which uses two-dimensional NMR techniques during a temperature and/or pressure cycle to quantify the asphaltene content of the crude oil without the need for extracting the oil from the reservoir rock. The technique can be applied to core, down-hole logs, or, a combination of both.