Low Salinity Waterflood Ion Diffusion Control
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Solution Overview
Problem
The effectiveness of low salinity waterflooding in hydrocarbon-bearing reservoirs with interbedded permeable and impermeable layers is reduced due to ion diffusion from high salinity connate water in shale layers into the injected low salinity water, leading to increased salinity and reduced oil recovery, especially when large volumes of high salinity connate water are present.
Innovation Solution
A computer-implemented method to determine the effectiveness of low salinity waterflood by calculating an ion diffusion distance value and comparing it to the thickness of permeable layers, and adjusting the injection velocity to maintain a target velocity, thereby optimizing the low salinity waterflood process and maximizing oil recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If low salinity water is injected into the reservoir to displace oil, then oil recovery is improved, but ion diffusion from shale layers increases salinity of the injected water reducing effectiveness
Solution Approach 1:
The patent calculates ion diffusion distance and compares it to permeable layer thickness before initiating the waterflood operation. This preliminary assessment allows operators to determine whether a low salinity waterflood will be effective, preventing waste of resources on unfavorable reservoirs where ion diffusion would quickly degrade the injected water quality
Solution Approach 2:
The patent identifies reservoirs where ion diffusion would harm the waterflood effectiveness (when diffusion distance is large relative to layer thickness) and prevents the harmful action by not conducting low salinity waterflood in these cases. The method proactively avoids the problem rather than trying to mitigate it during operation
2Productivity
If injection velocity is increased to improve oil production rate, then productivity increases, but ion diffusion from shale layers increases reducing water quality
Solution Approach 1:
The patent establishes a relationship between injection velocity and residence time, and consequently between injection velocity and ion diffusion distance. By controlling the injection velocity parameter, operators can manage the residence time of water in the permeable layers, thereby controlling the extent of ion diffusion from shale layers and maintaining water quality within acceptable ranges
3Productivity
If low salinity water is used to displace oil from sandstone layers, then oil recovery from sandstone improves, but shale layers remain saturated with high salinity connate water
Solution Approach 1:
The patent uses analytical solutions to Fick's law of diffusion to create a simplified model that replicates the complex ion diffusion behavior between shale and sandstone layers. This copying approach allows rapid evaluation of diffusion effects without requiring full numerical simulation, enabling quick assessment of whether ion diffusion will significantly impact waterflood effectiveness
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 the efficient use of limited low salinity water by ensuring only effective low salinity waterfloods are performed, maintaining optimal velocity to balance oil recovery and water flow, and determining well locations to minimize ion diffusion impacts, thereby enhancing the incremental oil recovery.
Implementation Method 1
the diffusion of ions from higher salinity connate water present in the pore space of the shale layers into the low salinity water that is flowing through the adjacent sandstone layer
Data Source
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AI summary
Methods, apparatuses and computer readable instructions for determining the effectiveness of, and for performing, a low salinity waterflood. An ion diffusion distance value is determined based on the rate of diffusion of ions within the rock of a reservoir and the residency time of floodwater within the reservoir. The thickness of the layers of the reservoir are compared to this ion diffusion value to determine the effectiveness of performing a low salinity waterflood and also to enable the effective control of a waterflood and to assist in the determination of locations of wells.