NMR Well Logging Depth Saturation Estimation
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Solution Overview
Problem
Nuclear magnetic resonance (NMR) well logging instruments typically measure properties at shallow depths, which may not represent natural water saturation in subsurface rock formations due to drilling fluid infiltration, especially with oil-based drilling fluids displacing connate hydrocarbons, leading to uncertainties in hydrocarbon saturation estimation.
Innovation Solution
A method to estimate fluid saturation by measuring NMR properties at multiple lateral depths, calculating bound and free water volumes, and determining a relationship between depth and water saturation to extend estimates beyond the instrument's measurement depth, using a wireline or logging-while-drilling NMR instrument.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NMR measurements are made at shallow depths near the wellbore, then measurement precision is improved, but the water saturation becomes unrepresentative of natural formation saturation due to drilling fluid infiltration
Solution Approach 1:
The patent transitions from single-depth measurements to multi-depth measurements by acquiring NMR data at multiple radial distances from the wellbore. This dimensional expansion allows differentiation between invaded zone (drilling fluid affected) and uninvaded zone (natural formation) saturations, resolving the contradiction between measurement accessibility and representativeness.
Solution Approach 2:
The method performs preliminary measurements at multiple depths before making the final estimation. By collecting NMR data at several radial positions and establishing the depth-saturation relationship in advance, the system prepares the necessary information to extrapolate accurate deep formation saturation values that are not directly measurable.
2Reliability
If measurements are extended to greater lateral depths, then representativeness of natural water saturation is improved, but measurement capability is exceeded due to instrument depth limitations
Solution Approach 1:
The patent introduces an intermediate mathematical model (the relationship between lateral depth and water saturation) that acts as a mediator between measurable depths and unmeasurable depths. This model, derived from measurements at accessible depths, enables indirect estimation of saturation at greater depths where the instrument cannot directly measure, thus extending measurement capability through mathematical interpolation/extrapolation.
Solution Approach 2:
The system performs preliminary measurements at multiple depths within the instrument's capability range, establishes the depth-saturation relationship model in advance, and then uses this pre-established model to estimate saturation at greater depths. This preliminary action allows the system to overcome instrument depth limitations through mathematical extrapolation.
3Productivity
If oil-based drilling fluids are used, then drilling efficiency is improved, but hydrocarbon displacement and saturation estimation uncertainty increase
Solution Approach 1:
The patent segments the formation into multiple radial zones (invaded zone and uninvaded zone) based on drilling fluid penetration depth. By measuring and analyzing saturation separately in each zone, the method identifies the boundary where drilling fluid effects cease, allowing accurate estimation of original hydrocarbon saturation in the uninvaded zone despite the presence of oil-based drilling fluid in the invaded zone.
Solution Approach 2:
The depth-saturation relationship model serves as an intermediary that connects measurements from the invaded zone to the uninvaded zone. This model accounts for the gradual transition of saturation values with depth, enabling accurate extrapolation to the original formation saturation beyond the drilling fluid influence, thus resolving the uncertainty caused by oil-based drilling fluid usage.
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 method provides more accurate estimation of water saturation and hydrocarbon content at greater depths, improving the evaluation of fluid production properties in subsurface rock formations by minimizing the impact of drilling fluid infiltration.
Implementation Method 1
Nuclear magnetic resonance (NMR) well logging instruments known in the art make measurements related to certain nuclear magnetization properties of subsurface fluids in the rock formations
Data Source
AI summary
A method for estimating fluid saturation in a formation penetrated by a wellbore from nuclear magnetic resonance measurements made at a plurality of lateral depths into the formation from the wellbore includes estimating a bound water volume, a total porosity and a free water volume at each of the lateral depths from the nuclear magnetic resonance measurements. A minimum water saturation is estimated at each lateral depth from the total porosity, the free water volume and the bound water volume at each lateral depth. A value of water saturation is estimated at each lateral depth from the minimum water saturation at each lateral depth. A relationship between lateral depth and water saturation is determined. Water saturation is estimated at a selected lateral depth greater than the greatest lateral depth of the nuclear magnetic resonance measurements.