Monobore Drilling with Managed Pressure and Gas Draw
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Solution Overview
Problem
Conventional wellbore drilling operations require intermediate casings to prevent fracturing of shallower strata, increasing construction time and cost due to the need to pause drilling and trip out the drill string for casing installation.
Innovation Solution
A method involving drilling a first section with a specific fracture and pore pressure, applying backpressure, and drilling a second section using mud with a weight less than the pore pressure to draw gas from the formation, monitoring annulus pressure, and adjusting backpressure to maintain stability within the mud weight window.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If intermediate casings are installed to prevent fracturing of shallower strata, then wellbore stability is improved, but drilling time increases due to pausing operations for casing installation
Solution Approach 1:
The patent extracts the intermediate casing requirement by using gas draw to create a pressure regime that prevents fracturing of shallower strata without physical casings. The gas draw mechanism removes the need for intermediate casings by maintaining annulus pressure within the mud weight window throughout the wellbore, allowing continuous drilling through previously problematic depth zones.
Solution Approach 2:
The patent changes the pressure parameter by applying gas draw to reduce annulus pressure in shallower sections. By controlling the gas draw rate and monitoring annulus pressure, the system maintains pressure below fracture gradients in upper formations while enabling drilling through deeper, higher-pressure zones, thereby eliminating the need for intermediate casings.
2Reliability
If intermediate casings are installed to isolate strata from drilling mud, then pressure stability is improved, but operational complexity increases due to tripping out drill string
Solution Approach 1:
The patent removes the intermediate casing isolation function by using gas draw to create a stable pressure regime that naturally prevents formation fracturing. The gas draw mechanism replaces the physical isolation provided by casings with a pressure control mechanism, eliminating the need to trip the drill string for casing installation and cementing operations.
Solution Approach 2:
The gas draw mechanism serves multiple functions simultaneously: it controls annulus pressure to prevent fracturing, enables continuous drilling through varying pressure zones, and eliminates the need for intermediate casings. This multi-functional approach simplifies the overall drilling system by replacing multiple discrete operations (casing installation, tripping, cementing) with a continuous gas draw process.
3Strength
If mud weight is increased to prevent plastic deformation at greater depths, then wellbore strength is improved, but fracture risk increases in shallower formations
Solution Approach 1:
The patent changes the pressure parameter by using gas draw to reduce annulus pressure in shallower sections. By controlling the gas draw rate, the system maintains annulus pressure below fracture gradients in upper formations while enabling drilling through deeper, higher-pressure zones, thereby eliminating the need for intermediate casings.
Solution Approach 2:
The patent implements dynamic pressure control through gas draw rather than static mud weight selection. The gas draw rate can be adjusted in real-time based on depth, formation characteristics, and monitored annulus pressure, allowing the system to adapt to varying pressure regimes throughout the wellbore without requiring intermediate casings.
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 or eliminates the need for intermediate casings, maintaining wellbore and pressure stability while reducing drilling time and cost by allowing continuous drilling operations.
Implementation Method 1
using drilling mud having a mud weight less than the second pore pressure to draw gas from a formation around the second section into the wellbore
Implementation Method 2
applying a backpressure on the wellbore
Data Source
AI summary
A method for drilling a wellbore comprises using drilling mud having a mud weight less than the formation pore pressure while drilling the horizontal section, to release some formation gas to mix with the drilling mud. As the mixture flows up the wellbore annulus, the resulting pressure in the vertical section is within the mud weight window (MWW) of the weak zones, thereby maintaining wellbore stability without the need for intermediate casings. The wellbore is killed by introducing a volume of heavy mud via a circulation sub in the drill string and periodically introducing additional heavy mud to fill the void left behind by the drill string as it is pulled uphole. The ratio of light mud and heavy mud in the killed well is such that the resulting pressure in the vertical section is within the MWW of the weak zones.