Fracture-Injection Falloff Test for Reservoir Transmissibility
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Solution Overview
Problem
Conventional methods for evaluating reservoir properties in subterranean formations, such as pressure-transient testing and fracture-injection/falloff analysis, are inefficient, inaccurate, and impractical for low permeability or multi-layered formations, particularly due to the need for extended test times and inability to quantify reservoir transmissibility effectively.
Innovation Solution
A method and system for determining reservoir transmissibility using a fracture-injection/falloff test, which involves isolating a subterranean layer, injecting fluid at pressures exceeding fracture pressure, shutting in the well, and analyzing pressure falloff data with a fracture-injection/falloff test model to quantify transmissibility, allowing for rapid estimation of formation properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional pressure-transient testing is used to evaluate reservoir properties, then measurement precision is improved, but test duration becomes excessively long (several days to weeks)
Solution Approach 1:
The patent applies preliminary action by performing a fracture treatment (injection) before the evaluation test. The fracture creates enhanced communication between the wellbore and formation, allowing pressure transient data to be obtained much more quickly while still providing accurate reservoir property evaluation. The fracture is created in advance to eliminate the need for long test durations.
Solution Approach 2:
The patent changes the physical state of the formation by inducing fractures through injection pressure exceeding fracture pressure. This parameter change (from intact to fractured formation) fundamentally alters the pressure transient response characteristics, enabling rapid evaluation while maintaining measurement precision through analysis of the modified pressure falloff behavior.
2Measurement precision
If conventional fracture-injection/falloff analysis is used, then reservoir evaluation is performed, but only small portions of pressure decline data can be quantitatively analyzed and extended shut-in periods are required
Solution Approach 1:
The patent applies dynamics by using a variable-rate injection approach during the fracture creation phase, followed by a controlled falloff period. The injection rate is dynamically adjusted to create the fracture efficiently, then stopped to allow pressure falloff. This dynamic approach enables complete utilization of pressure decline data for transmissibility calculation without requiring extended shut-in periods for pseudoradial flow observation.
Solution Approach 2:
The patent ensures continuity of useful action by analyzing the entire pressure decline curve from the moment injection stops until pressure stabilizes. Unlike conventional methods that only analyze specific portions, this approach continuously utilizes all available pressure falloff data points to calculate transmissibility, maximizing information extraction from the test while minimizing required shut-in time.
3Measurement precision
If conventional methods are used for low permeability formations, then formation evaluation is attempted, but test times extend to weeks or months and cost-effectiveness deteriorates
Solution Approach 1:
For low permeability formations, the patent applies preliminary action by creating a fracture treatment before the evaluation test. This pre-created fracture provides enhanced communication pathways that allow pressure transient signals to propagate and be detected much more quickly in low permeability rock, enabling accurate formation property evaluation within hours rather than weeks or months, thereby restoring cost-effectiveness.
4Measurement precision
If conventional pressure-transient testing is used in multi-layered formations, then reservoir evaluation is performed, but isolated-layer testing requires weeks to months to evaluate all layers
Solution Approach 1:
The patent applies segmentation by isolating individual layers using packers or other isolation devices before performing the fracture-injection/falloff test on each layer separately. This segmentation allows each layer to be evaluated independently and quickly (in hours rather than weeks), while maintaining accurate layer-specific reservoir property measurement. The cumulative testing time for multiple layers is dramatically reduced compared to conventional sequential testing.
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 enables rapid and accurate determination of reservoir transmissibility, reducing test time and improving cost-effectiveness, making it suitable for evaluating both low permeability and multi-layered formations.
Implementation Method 1
introducing an injection fluid into the at least one layer of the subterranean formation at an injection pressure exceeding the subterranean formation fracture pressure
Implementation Method 2
measuring pressure falloff data from the subterranean formation during the injection period and during a subsequent shut-in period
Data Source
AI summary
Methods and systems are provided for evaluating subsurface earth oil and gas formations. More particularly, methods and systems are provided for determining reservoir properties such as reservoir transmissibilities and average reservoir pressures of a formation layer or multiple layers using fracture-injection/falloff test methods. The methods herein may use pressure falloff data generated by the introduction of an injection fluid at a pressure above the formation fracture pressure in conjunction with a fracture-injection/falloff test model to analyze reservoir properties. The fracture-injection/falloff test model recognizes that a new induced fracture creates additional storage volume in the formation and that a fracture-injection/falloff test in a layer may exhibit variable storage during the pressure falloff, and a change in storage may be observed at hydraulic fracture closure.