Nested Drill String for Thermally Insulated Geothermal Well Completion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional geothermal well construction methods face challenges such as mineral scaling and corrosion, thermal energy loss, groundwater pollution risk, limited fluid use, and soil instability, particularly in arctic regions, along with directional drilling difficulties and high Non Productive Time (NPT) in constructing long-reach horizontal wells.
Innovation Solution
The use of a nested drill string with an inner and outer pipe, where drilling fluid is pumped through the annular space between the pipes and drill cuttings are returned through the inner pipe, allowing for a low thermal conductivity fluid or vacuum in the annular space to minimize heat loss and enable a thermally insulated completion conduit, combined with a permeability barrier to stabilize the well.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional drilling and completion methods are used with fluid return in the well annulus, then drilling and completion can be performed, but thermal energy is lost and hot wellheads are created causing soil instabilities
Solution Approach 1:
The wellbore is segmented into two separate flow paths: one for circulating fluid through the formation (production) and another for returning drilling fluid or providing thermal insulation (annulus). This segmentation allows thermal energy to be retained in the production fluid while the annulus can be dedicated to insulation or separate fluid return, eliminating the mixing of hot production fluid with cooler annulus fluid that causes thermal losses and wellhead heating.
Solution Approach 2:
A nested conduit system is implemented where an inner production tubing is placed within an outer well casing, creating concentric annular spaces. The inner pipe carries production fluid while the outer annulus can be filled with insulation material or used for thermal isolation. This nested configuration provides thermal insulation between the hot production fluid and the wellhead environment, preventing soil instability and permafrost damage while minimizing thermal energy loss.
2Productivity
If a long-reach horizontal well is constructed with nested conduit, then geothermal heat extraction is improved, but Non Productive Time increases due to fluid loss, hole cleaning, high torque and drag
Solution Approach 1:
The nested conduit system utilizes hydraulic principles to manage drilling fluid circulation through the annular space between inner and outer pipes. By optimizing fluid flow characteristics, pressure gradients, and viscosity management in the annulus, the system reduces torque and drag on the drill string, improves hole cleaning efficiency, and minimizes fluid loss during drilling of long-reach horizontal sections, thereby reducing Non Productive Time.
3Loss of energy
If the annular space is evacuated or filled with low conductivity fluid, then thermal insulation is improved, but drilling and completion complexity increases
Solution Approach 1:
The thermal insulation performance is optimized by changing the physical parameters of the annular space medium. The annulus can be evacuated to create a vacuum (eliminating conduction and convection), or filled with gases or liquids having low thermal conductivity. This parameter change dramatically reduces heat transfer from the production fluid to the wellhead environment, providing effective thermal insulation while the added complexity is managed through standardized completion procedures.
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 method reduces drilling risks, minimizes heat loss, and enhances cost efficiency by enabling long-reach horizontal wells with reduced maintenance and environmental impact, facilitating geothermal energy production.
Implementation Method 1
a low thermal conductivity fluid or vacuum in the annular space to minimize heat loss and enable a thermally insulated completion conduit
Data Source
AI summary
A method to establish a well using a nested drill/completion string. The nested drill/completion string includes an inner pipe nested in an outer pipe, a flow crossover disposed at an end of the nested drill string and a drill bit disposed to one side of the flow crossover. Drilling fluid is pumped into the well through a first annular space between the inner pipe and the outer pipe, and drill cuttings created by the drill bit are returned to surface through in inner pipe. For the completion of the well, either (i) fluid in the annular space is displaced with a lower conductivity fluid or (ii) the annular space; is evacuated. Fluid to be heated is pumped through a second annular space between the well and the exterior of the nested drill string and geothermally heated fluid is moved from the subsurface to the surface through the inner pipe.