Cryogenic Acid Fracking for Carbonate Reservoirs

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Solution Overview

Problem

In deep, hot reservoirs, acid fracturing is economically uneconomic due to the rapid reaction of hydrochloric acid with the formation, leading to shallow acid penetration and high costs associated with chemical retardants, and existing methods struggle to effectively create long etched fractures in high permeability and naturally fractured carbonate formations.

Innovation Solution

The use of cryogenic carrier fluids to decrease the reaction rate of acid with carbonate-rich formations, allowing deeper penetration and creating thermal and mechanical stresses that form a rubble zone aiding in fracture propagation, thereby reducing blockages and increasing fracture network and hydrocarbon desorption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If conventional acid fracturing is used in deep, hot reservoirs, then the acid reacts rapidly with the formation, but this results in shallow acid penetration and high costs

Engineering Contradiction:

Improveacid penetration depthVSAvoidacid reaction rate control

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent changes the temperature parameter of the acid fluid by using cryogenic temperatures (e.g., liquid nitrogen at -196°C) to slow down the chemical reaction rate between acid and carbonate formation. This parameter change allows the acid to penetrate deeper into the formation before reacting, directly resolving the contradiction between penetration depth and reaction rate control.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces liquid nitrogen as an intermediary carrier fluid that delivers the acid to the formation. The liquid nitrogen maintains cryogenic temperatures during injection and phase changes, acting as a mediator that controls the acid's reaction rate while enabling deep penetration. This intermediary solution resolves the contradiction by providing temperature control without requiring complex chemical retardants.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Quantity of substance

If chemical retardants are added to slow acid reaction, then penetration depth improves, but treatment cost increases significantly

Engineering Contradiction:

Improveacid penetration depthVSAvoidtreatment cost

Core Design Contradiction:

Quantity of substanceVSEase of manufacture

Solution Approach 1:

The patent replaces the chemical system (chemical retardants) with a physical system (cryogenic temperature control using liquid nitrogen). This substitution eliminates the need for expensive chemical additives while achieving the same goal of slowing acid reaction and increasing penetration depth, thereby resolving the contradiction between penetration depth and treatment cost.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the fundamental parameter from chemical composition modification (adding retardants) to physical state modification (using cryogenic temperatures). This parameter change achieves deep acid penetration through physical temperature control rather than chemical additives, directly addressing the cost issue while maintaining effective penetration depth.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If high concentration acid is used to increase etching capability, then fracture conductivity improves, but reaction rate with formation increases, reducing penetration

Engineering Contradiction:

Improvefracture etching qualityVSAvoidacid penetration depth

Core Design Contradiction:

Manufacturing precisionVSQuantity of substance

Solution Approach 1:

The patent simultaneously optimizes two parameters: acid concentration (maintaining high etching capability) and temperature (using cryogenic conditions to slow reaction rate). This dual parameter control allows high concentration acid to penetrate deeper while maintaining strong etching capability, resolving the contradiction between etching quality and penetration depth.

Inventive Principle:

Principle #35Parameter changes

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

Cryogenic acid fracking slows down acid reaction, allowing deeper penetration, reduces water usage, eliminates hydraulic fracture-induced water blockage, increases fracture surface area, and forms rubblized shale particles that act as a natural proppant, enhancing production from carbonate-rich reservoirs.

Implementation Method 1

The use of cryogenic carrier fluids to decrease the reaction rate of acid with carbonate-rich formations

Methodology Applied

Scientific EffectThermal energy reduction: Cooling

Implementation Method 2

creating thermal and mechanical stresses that form a rubble zone aiding in fracture propagation

Methodology Applied

Scientific EffectThermal stress: Thermal Shock

Implementation Method 3

freezes immobile in situ water increasing pore pressure driving the reservoir rock into shear failure

Methodology Applied

Scientific EffectPhase change (freezing): Freezing

Data Source

PatentUS9644137B2Method of cryogenic acid fracking

Publication Date: 2017.05.09 CONOCOPHILLIPS CO

AI summary

A method of fracking carbonate-rich reservoirs, comprising injecting a cryogenic or chilled fluid followed by an acid into the reservoir, allowing the acid to etch the reservoir, and thereby increasing production of a fluid, such as water, oil or gas, from the reservoir. Further, injecting a preflush into the reservoir and later injecting a postflush into the reservoir to displace the acid from the tubulars into the reservoir.