NMR Logging Tool Permeability Measurement in Tight Formations
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Solution Overview
Problem
Current NMR logging tools face challenges in accurately measuring permeability and pore pressure in tight formations like shale gas, where low permeability prevents significant gas flow to the borehole, and existing methods are inefficient in differentiating between drilling-induced micro-fractures and natural permeability.
Innovation Solution
An NMR logging tool system is deployed with packers to isolate a wellbore section, evacuate, and inject fluid to specific pressures, allowing time-dependent NMR measurements to differentiate between micro-crack and natural permeability contributions, enabling accurate permeability and pore pressure determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional NMR logging tools are used to measure permeability in tight formations, then the measurement process is simple, but the measurement precision is poor due to low gas flow to the borehole
Solution Approach 1:
The wellbore is segmented into isolated sections using packers, creating distinct measurement zones. This allows separate characterization of micro-fracture permeability and natural permeability by isolating different formation regions, thereby improving measurement precision without requiring complex multi-tool systems
Solution Approach 2:
The formation is pressurized before NMR measurement to ensure gas flow into the borehole, creating favorable flow conditions. This preliminary pressurization action enables accurate permeability measurement in tight formations where gas flow would otherwise be insufficient, improving measurement precision while maintaining relatively simple tool geometry
2Measurement precision
If NMR measurements are made without pressure control, then the operation is simple, but the measurement precision is poor due to inability to differentiate micro-fracture and natural permeability
Solution Approach 1:
The system dynamically controls formation pressure during measurement sequences, transitioning between different pressure states to activate different flow pathways. By varying pressure conditions, the system can isolate and measure micro-fracture permeability separately from natural permeability, achieving precise differentiation while maintaining straightforward operational procedures through automated pressure control
Solution Approach 2:
Pressure sensors provide real-time feedback on formation pressure during NMR measurements, enabling automated adjustment of pressure conditions to optimize gas flow. This feedback mechanism ensures accurate permeability differentiation between micro-fractures and natural pathways while simplifying operation through automated control rather than manual intervention
3Reliability
If gas is injected at high pressure to improve signal strength, then the NMR signal strength increases, but the formation may experience pressure-induced fractures or fluid injection problems
Solution Approach 1:
The formation is pre-pressurized to a controlled level before NMR measurement, establishing stable pressure conditions that prevent sudden pressure shocks. This preliminary action ensures reliable NMR signaling while avoiding pressure-induced fractures or fluid injection problems that would occur with abrupt high-pressure injection
Solution Approach 2:
The system carefully controls and varies pressure parameters within safe limits, using optimized pressure levels that maximize NMR signal strength without exceeding formation integrity thresholds. By precisely managing pressure as a variable parameter, the system achieves reliable measurements while preventing harmful pressure-induced effects in the formation
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
The system effectively measures permeability and pore pressure by analyzing the time-dependent NMR signal build-up, distinguishing between micro-crack and natural permeability contributions, providing reliable data even in low-permeability formations.
Implementation Method 1
Nuclear Magnetic Resonance (NMR) tools used for well-logging and downhole fluid characterization measure the response of nuclear spins in formation fluids to applied magnetic fields
Implementation Method 2
Downhole NMR tools typically have a permanent magnet that produces a static magnetic field at a desired test location
Implementation Method 3
The static magnetic field produces a magnetization in the fluid. The magnetization is aligned along the direction of the static field
Implementation Method 4
A transmitter antenna produces a time-dependent radio frequency magnetic field that has a component perpendicular to the direction of the static field
Implementation Method 5
The rotation results in the magnetization vector developing a component perpendicular to the direction of the static magnetic field. This causes the magnetization vector to precess around the static field at the Larmor frequency
Implementation Method 6
Packers are provided and actuated to hydraulically isolate a section of the wellbore and form a cavity between the NMR logging tool and the wall of the isolated section of the wellbore
Implementation Method 7
The cavity is evacuated until a first desired pressure within the cavity is attained. Fluid is injected into the cavity until a second desired pressure within the cavity is attained
Implementation Method 8
For a fluid of unit viscosity, these quantities are related to the sample permeability, k, through Darcy's law: q = k * ΔP
Data Source
AI summary
A NMR logging tool is provided and disposed in a wellbore at some desired depth. Packers are provided and actuated to hydraulically isolate a section of the wellbore and form a cavity between the NMR logging tool and the wall of the isolated section of the wellbore. The cavity is evacuated until a first desired pressure within the cavity is attained. Fluid is injected into the cavity until a second desired pressure within the cavity is attained. A plurality of NMR measurements is made on the region of the formation, each of the plurality of measurements being made at different times. Formation properties are inferred using the measurements. A baseline NMR measurement may be made when a first desired pressure is attained. A time-zero NMR measurement may be made when a second desired pressure is attained. Similar measurements may be made in a laboratory on a sample.