Drilling Fluid Polymer Blend Shear Thinning Viscosity Control
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Solution Overview
Problem
Conventional drilling fluids face challenges in controlling fluid and cutting loss during borehole drilling, particularly in unconsolidated or fractured formations, leading to increased tool wear, decreased drilling rates, and borehole instability.
Innovation Solution
A drilling fluid comprising a blend of xanthan gum, low molecular weight partially-hydrolysed polyacrylamide (PHPA), and low viscosity polyanionic cellulose (Pac-LV), which exhibits a unique shear thinning property, increasing viscosity in low shear rates to block loss zones while maintaining low viscosity at high shear rates for efficient cutting transport.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional drilling fluids with solid bridging agents are used to control fluid loss, then fluid and cutting loss is reduced, but downhole motors are damaged and pore throats are plugged
Solution Approach 1:
The patent replaces solid bridging agents (mechanical particles) with a polymer-based chemical system that controls fluid loss through viscosity modification and gel structure formation. The polymer blend creates a gel network that plugs loss zones without requiring solid particles, thereby preventing damage to downhole motors and avoiding plugging of pore throats.
Solution Approach 2:
The patent utilizes shear-dependent viscosity changes of the polymer blend to control fluid loss. The fluid exhibits high viscosity at low shear rates (blocking loss zones) and low viscosity at high shear rates (allowing circulation). This parameter change enables fluid loss control without solid particles that could damage equipment.
2Productivity
If drilling fluid viscosity is increased to suspend and transport cuttings, then cutting removal is improved, but fluid loss into formations increases
Solution Approach 1:
The patent employs a dynamic viscosity system where the polymer blend's viscosity changes with shear rate. During circulation (high shear), viscosity is low for efficient fluid flow and cutting transport. When fluid contacts loss zones (low shear), viscosity increases to block fluid loss. This dynamic adaptation resolves the contradiction between cutting transport and fluid loss control.
Solution Approach 2:
The patent changes the viscosity parameter of the drilling fluid based on flow conditions. The polymer blend exhibits shear-thinning behavior, maintaining low viscosity during high-speed circulation for cutting removal, while increasing viscosity at low shear rates to seal loss zones, thereby simultaneously achieving both cutting transport and fluid loss control.
3Loss of substance
If solid particles are added to control fluid loss, then permeability of loss zone decreases, but tool wear increases and drilling rate decreases
Solution Approach 1:
The patent substitutes solid particle-based fluid loss control with a polymer-based chemical system. The polymer blend forms gel structures and modifies fluid rheology to control loss without introducing solid particles that would cause tool wear and reduce drilling rate. This eliminates the harmful effects of solid bridging agents while maintaining fluid loss control 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
The fluid effectively reduces fluid and cutting loss, enhances drilling stability, and prevents borehole instability by selectively increasing viscosity in loss-prone formations while maintaining operational efficiency.
Implementation Method 1
the drilling fluids disclosed herein comprise natural and synthetic polymer blends that are effective to provide the fluid with a high viscosity under low shear rates and a low viscosity under high shear rates
Data Source
AI summary
The present invention relates to drilling fluids which reduce fluid and cutting loss during the drilling of subterranean wells. More specifically, the drilling fluids disclosed herein comprise natural and synthetic polymer blends that are effective to provide the fluid with a high viscosity under low shear rates and a low viscosity under high shear rates. The present invention also relates to methods for using the drilling fluids for reducing fluid and cutting loss during drilling.