Thixotropic Cement Slurry for Lost Circulation Plugging
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Solution Overview
Problem
Conventional cement compositions and placement methods for isolating lost circulation zones during well construction often result in high fluid loss to the formation, increasing costs and downtime.
Innovation Solution
A thixotropic cement slurry comprising cement, viscosifier, mix water, and strength accelerating additives, combined with a 'pump and pull' placement method, is used to create a plug in the wellbore, reducing lost circulation by increasing viscosity with no shear and decreasing viscosity with shear, allowing the slurry to harden and form a effective seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cement compositions and placement methods are used to isolate lost circulation zones, then the wellbore can be sealed, but high fluid loss to the formation occurs, increasing costs and downtime
Solution Approach 1:
The patent applies parameter changes by modifying the rheological properties of cement slurry through thixotropic additives, changing its viscosity behavior from conventional to thixotropic. This allows the slurry to maintain low viscosity during pumping (reducing fluid loss) while developing high viscosity at rest (improving sealing effectiveness). The power law exponent is specifically controlled to be between -0.5 and 0.3 to achieve this thixotropic behavior.
Solution Approach 2:
The patent implements dynamics by using a cement slurry whose viscosity dynamically changes based on shear conditions. During pumping operations, the slurry exhibits low viscosity for easy flow and minimal fluid loss. Once placed in the wellbore, the slurry transitions to high viscosity to maintain plug integrity and prevent fluid loss. This dynamic rheological adaptation resolves the contradiction between sealing effectiveness and fluid loss.
2Reliability
If conventional cement placement methods are used, then the wellbore can be plugged, but excessive hydrostatic pressure and overbalance are experienced, reducing placement effectiveness
Solution Approach 1:
The patent applies parameter changes by utilizing the thixotropic property of the cement slurry to alter its flow characteristics. The slurry maintains low viscosity during pumping, enabling placement at lower pressures and reducing hydrostatic pressure buildup. Once placed, the viscosity increases to ensure effective plugging. This parameter change resolves the contradiction between plugging effectiveness and pressure management.
Solution Approach 2:
The thixotropic cement slurry acts as an intermediary material that mediates between the pumping system and the wellbore formation. Its unique rheological properties allow it to be pumped at low pressure while still achieving effective placement and plugging. The slurry bridges the gap between low-pressure delivery requirements and high-integrity plugging requirements, resolving the pressure-effectiveness contradiction.
3Reliability
If multiple plugging attempts are made to isolate losses, then the lost circulation zone can be sealed, but rig non-productive time increases
Solution Approach 1:
The patent applies preliminary action by incorporating thixotropic additives into the cement slurry formulation before placement. This preliminary modification ensures the slurry has the optimal rheological properties for single-attempt successful plugging. The pre-engineered thixotropic behavior eliminates the need for multiple attempts, thereby reducing rig non-productive time while maintaining reliable lost circulation isolation.
Solution Approach 2:
The patent uses parameter changes in the cement slurry's rheological properties (specifically the power law exponent between -0.5 and 0.3) to achieve effective plugging in a single attempt. This parameter optimization ensures proper flow during pumping and adequate set characteristics, eliminating the need for repeated plugging operations and reducing time loss.
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 reduces the number of plugging attempts needed, lowers rig non-productive time, and effectively isolates lost circulation zones without excessive hydrostatic pressure, applicable in both onshore and offshore environments.
Implementation Method 1
thixotropic means the thixotropic cement slurry will increase in viscosity with no shear and decrease in viscosity with shear
Data Source
AI summary
Embodiments of methods for reducing lost circulation in a wellbore comprise inserting a conduit comprising a first and second end and an outer diameter and an inner diameter into the wellbore, and pumping a thixotropic cement slurry, wherein the thixotropic cement slurry will increase in viscosity with no shear and decrease in viscosity with shear, and have a power law exponent value of less than or equal to 0.3 when the thixotropic cement slurry has a density of greater than 12.69 pounds per gallon, through the conduit into the wellbore, in which the thixotropic cement slurry comprises at least one cement, at least one viscosifier, mix water, and one or more than one strength accelerating additives. The method further comprises allowing the thixotropic cement slurry to harden in the wellbore to create a plug, removing the conduit from the wellbore, and reducing lost circulation via the plug in the wellbore.