Micro-proppant Sealing for Pressure Dependent Leak-off Mitigation
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Solution Overview
Problem
In unconventional formations like shale and tight sandstone, pressure-dependent leak-off (PDL) in secondary fractures hinders hydraulic fracturing efficiency, as conventional proppants cannot enter or prop open these small fractures, leading to fluid loss and increased pressures required for dominant fracture growth, which delays well completion and incurs financial losses.
Innovation Solution
The use of micro-proppants, specifically ceramic microspheres smaller than 149 μm, is introduced into the formation to seal and divert fluid flow from PDL fractures to primary fractures, either ahead of or behind acid treatments, thereby reducing fluid loss and maintaining acid effectiveness on dominant fractures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional proppants (100 mesh or 40/70 mesh) are used in hydraulic fracturing, then dominant hydraulic fractures can be propped open, but secondary PDL fractures cannot be entered or propped, leading to fluid loss and increased pressures
Solution Approach 1:
The patent segments the propping function by using two different proppant sizes: conventional proppants (100 mesh or 40/70 mesh) for dominant hydraulic fractures and micro-proppants (200-400 mesh) for secondary PDL fractures. This segmentation allows each proppant type to perform its specialized function in the appropriate fracture size range, resolving the contradiction between propping effectiveness and fluid loss.
Solution Approach 2:
The patent applies local quality by introducing micro-proppants specifically into secondary PDL fractures where their fine size (200-400 mesh) provides the appropriate bridging capability for these small fractures. Meanwhile, conventional proppants remain in dominant fractures where larger size is beneficial. This localized application of different proppant qualities optimizes both fracture types without compromise.
2Stress or pressure
If higher pressures are applied to propagate dominant hydraulic fractures, then fracture growth can be maintained, but fluid is diverted to secondary fractures causing treatment rate delays
Solution Approach 1:
The patent applies preliminary action by injecting micro-proppants into secondary PDL fractures before the main fracturing treatment. This pre-propping of secondary fractures prevents them from acting as fluid sinks during subsequent high-pressure injection, eliminating the need to apply excessive pressures to maintain dominant fracture growth and preventing treatment rate delays.
Solution Approach 2:
The patent converts the harmful effect of secondary PDL fractures (which normally cause fluid theft and pressure increases) into a benefit by using them as delivery pathways for micro-proppants. The same fractures that would normally harm productivity are utilized to place the fine proppants that subsequently prevent fluid loss, turning the problem into a solution.
3Strength
If HF/HCl or HCl acid mixtures are used to initiate hydraulic fractures in tight sandstone, then fracture initiation is improved, but PDL is exacerbated due to acid dissolving power
Solution Approach 1:
The patent applies preliminary anti-action by injecting micro-proppants into secondary PDL fractures before introducing HF/HCl or HCl acid mixtures. The micro-proppants create a physical barrier that prevents acid from excessively dissolving the formation in secondary fractures, thereby preventing PDL exacerbation while allowing the acid to effectively initiate dominant hydraulic fractures.
Solution Approach 2:
The micro-proppants serve as an intermediary between the acid mixture and the formation in secondary PDL fractures. They physically block the acid from直接接触 the formation, preventing the harmful dissolving effect that would exacerbate PDL, while still allowing the acid to reach and initiate dominant fractures where it is needed.
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 effectively reduces PDL, allowing for more efficient hydraulic fracturing by ensuring fluid is directed to primary fractures, reducing the need for elevated pressures and accelerating well completion, thus minimizing delays and operational costs.
Implementation Method 1
The micro-proppant can either be pumped ahead of the acid, behind the acid, or both. Other large proppants such as 100 mesh proppant can be used in conjunction with the micro-proppant.
Implementation Method 2
allowing a portion of the micro-proppant particulates in the first fluid to divert a flow of at least a portion of the acid from the PDL fractures to a primary fracture
Implementation Method 3
Hydraulic fracturing is a primary tool for improving well productivity by placing or extending channels from the wellbore to the reservoir. This operation is essentially performed by hydraulically injecting a fracturing fluid into a wellbore penetrating a subterranean formation and forcing the fracturing fluid against the formation strata by pressure. The formation strata or rock is forced to crack and fracture.
Data Source
AI summary
Methods for reducing pressure dependent leak-off (PDL) in PDL fractures of an unconventional subterranean formation are described. The methods include introducing a first fluid including micro-proppant particulates into the formation, allowing a portion of the micro-proppant particulates in the first fluid to seal one or more PDL fractures in the formation, pumping an acid into the formation, allowing a portion of the micro-proppant particulates in the first fluid to divert a flow of at least a portion of the acid from the PDL fractures to a primary fracture, introducing a second fluid including micro-proppant particulates into the formation, and allowing a portion of the micro-proppant particulates in the second fluid to seal one or more PDL fractures in the formation.