US2016305231A1PendingUtilityA1
System and Method for Drilling using Pore Pressure
Est. expiryApr 14, 2035(~8.8 yrs left)· nominal 20-yr term from priority
E21B 49/003E21B 47/06E21B 45/00E21B 44/06E21B 44/04
20
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Claims
Abstract
A system and method for drilling a borehole in a subsurface formation. A method includes rotating a drill bit to remove formation material from the subsurface formation at an end of the borehole. A value of mechanical specific energy applied to remove the formation material is calculated. A value of drilling efficiency is calculated based on the value of mechanical specific energy. Pore pressure of the subsurface formation in contact with the drill bit is calculated as a function of calculated drilling efficiency. Real-time operational decisions (such as adjusting density of drilling fluid or determining the final depth of the hole section) are made based on calculated pore pressure of the subsurface formation.
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1 . A method for drilling a borehole in a subsurface formation, comprising:
rotating a drill bit to remove formation material from the subsurface formation at an end of the borehole; calculating a value of mechanical specific energy applied to remove the formation material; calculating a value of drilling efficiency based on the value of mechanical specific energy; calculating pore pressure of the subsurface formation in contact with the drill bit as a function of calculated drilling efficiency; and controlling the drilling based on calculated pore pressure of the subsurface formation.
2 . The method of claim 1 , further comprising:
acquiring a measurement of downhole torque applied at the drill bit and weight on bit applied at the drill bit to perform the rotating; and calculating the value of mechanical specific energy based on the acquired measurement of torque and weight on bit at the drill bit.
3 . The method of claim 1 , further comprising:
calculating the pore pressure based on a product of the value of mechanical specific energy and the calculated drilling efficiency; and calculating the pore pressure based on an angle of internal friction derived from offset well data.
4 . The method of claim 1 , further comprising:
calculating confined compressive strength of the formation based on normal pore pressure; and calculating the value of drilling efficiency as a ratio of the calculated confined compressive strength to the value of mechanical specific energy.
5 . The method of claim 1 , further comprising:
calculating a trend of normal drilling efficiency based on pressure data from an offset well; and calculating the pore pressure as a function of a difference of the value of drilling efficiency and the trend of normal drilling efficiency.
6 . The method of claim 1 , further comprising:
determining whether the calculated pore pressure is within a predetermined pressure range; and controlling the drilling operation responsive to the calculated pore pressure being within the predetermined pressure range; wherein controlling the drilling comprises at least one of changing drilling fluid density and changing drill bit movement.
7 . The method of claim 1 , wherein the pore pressure of the subsurface formation is calculated prior to a formation parameter measurement tool disposed uphole of the drill bit reaching a location of the subsurface formation corresponding to the calculated pore pressure.
8 . A system for drilling a borehole in a subsurface formation, comprising:
a drill string; a drill bit positioned at an end of the drill string to extend the borehole into the subsurface formation; and a drilling control system comprising:
a pore pressure calculator configured to calculate pore pressure of the formation in contact with the drill bit, the pore pressure calculator configured to:
calculate a value of drilling efficiency for the drilling of the borehole based on a drilling parameter measured at the bit; and
calculate the pore pressure as a function of the calculated value of drilling efficiency; and
drilling control logic configured to control the drilling based on calculated pore pressure.
9 . The system of claim 8 , wherein the pore pressure calculator is configured to:
calculate a value of mechanical specific energy applied to drill the formation; and calculate the value of drilling efficiency based on the value of mechanical specific energy.
10 . The system of claim 9 , wherein the pore pressure calculator is configured to:
acquire a measurement of torque applied at the drill bit and weight on bit applied at the drill bit to drill the formation; and calculate the value of mechanical specific energy based on the acquired measurement of torque and weight on bit at the drill bit.
11 . The system of claim 10 , wherein the measurement of torque applied at the drill bit is acquired in a bottom hole assembly of the drill string; or the measurement of torque applied at the drill bit is a measurement of torque applied in a 1/10 of the drill string nearest the drill bit.
12 . The system of claim 8 , wherein the pore pressure calculator is configured to calculate the pore pressure based on mechanical specific energy.
13 . The system of claim 8 , wherein the pore pressure calculator is configured to:
calculate confined compressive strength of the formation based on normal pore pressure; and calculate the value of drilling efficiency as a ratio of calculated confined compressive strength to the value of mechanical specific energy.
14 . The system of claim 8 , wherein the pore pressure calculator is configured to:
calculate a trend of normal drilling efficiency based on pressure data from an offset well; and calculate the pore pressure as a function of a difference of the value of drilling efficiency and the trend of normal drilling efficiency.
15 . The system of claim 8 , wherein the drilling control logic is configured to:
determine whether the calculated pore pressure is within a predetermined pressure range; and change at least one of drilling fluid density and drill bit movement responsive to the calculated pore pressure being within the predetermined pressure range.
16 . A system for calculating pore pressure of a subsurface formation, comprising:
a processor; a storage device coupled to the processor and containing instructions that when executed cause the processor to:
calculate a value of mechanical specific energy applied at a drill bit to remove material from the subsurface formation;
calculate a value of drilling efficiency for drilling the formation; and
calculate pore pressure of the formation in contact with the drill bit as a function of the value of drilling efficiency and the mechanical specific energy.
17 . The system of claim 16 , wherein the instructions cause the processor to:
acquire a measurement of torque applied at the drill bit to remove the material from the subsurface formation; calculate the value of mechanical specific energy based on the acquired measurement of torque applied at the drill bit; and calculate the pore pressure based on a product of the value of mechanical specific energy and the value of drilling efficiency.
18 . The system of claim 16 , wherein the instructions cause the processor to:
calculate confined compressive strength of the formation based on normal pore pressure; calculate the value of drilling efficiency as a ratio of the calculated confined compressive strength to the value of mechanical specific energy; calculate a trend of normal drilling efficiency based on pressure data received from an offset well; and calculate the pore pressure as a function of a difference of the value of drilling efficiency and the trend of normal drilling efficiency.
19 . The system of claim 16 , wherein the instructions cause the processor to calculate the pore pressure as:
p
=
p
n
+
Δ
DE
×
MSE
×
(
1
-
sin
θ
1
+
sin
θ
)
,
where:
p is calculated pore pressure;
p n is normal hydrostatic pressure;
ΔDE is a difference of the value of drilling efficiency and a trend of normal drilling efficiency;
MSE is the value of mechanical specific energy; and
θ is angle of internal friction.
20 . The system of claim 16 , wherein the instructions cause the processor to calculate the pore pressure as:
p
=
ECD
-
(
DE
trend
×
MSE
-
UCS
)
×
(
1
-
sin
θ
1
+
sin
θ
)
,
where:
p is calculated pore pressure;
ECD is equivalent circulating density;
DE trend is a trend of normal drilling efficiency;
MSE is the value of mechanical specific energy;
UCS is unconfined compressive strength; and
θ is angle of internal friction.Cited by (0)
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