Method for monitoring seafloor movements
View Patent ↗Seafloor movements are monitored by measuring the ambient seawater pressure at a plurality of locations adjacent to the seafloor using asynchronous pressure signals generated by a plurality of pressure sensors mounted at different locations on the seafloor over a prolonged period of time(t), wherein harmonic tide-related pressure variations on the asynchronous pressure signals are corrected by an algorithm comprising a mathematical equation that models spatial and temporal pressure variations in an objective function. The method is unconstrained with regard to the synchronicity of depth and/or pressure measurements and does not require additional stationary short tem local reference measurements.
1. A method for monitoring vertical seafloor movements by measuring the ambient seawater pressure at a plurality of locations adjacent to the seafloor comprising generating asynchronous pressure signals by a plurality of pressure sensors mounted at different locations on the seafloor over a prolonged period of time(t), and deriving tide-free relative height differences from the asynchronous pressure signals wherein the asynchronous pressure signals are corrected for harmonic tide-related pressure variations by an algorithm comprising a mathematical equation that models spatial and temporal pressure variations in an objective function and minimizing said objective function.
2. The method of claim 1 , wherein the algorithm comprises the mathematical equation:
p
(
t
,
x
)
=
A
0
(
x
,
t
)
+
A
T
(
t
)
+
∑
k
=
1
M
A
k
sin
(
ω
k
t
+
Φ
k
)
,
wherein x denotes the locations of the sensors, A 0 denotes a depth dependent offset which depends on location, A T denotes long-time or non-oscillatory variations, and the oscillatory terms:
∑
k
=
1
M
A
k
sin
(
ω
k
t
+
Φ
k
)
are determined by the amount M of tidal cycles k over the prolonged period of time(t), wherein ω k denotes frequencies of the tidal cycles, which are dictated by the motion of the earth with respect to the moon and the sun, and Φ k denotes phases of the tidal cycles that are associated with the location of the area in question.
3. The method of claim 2 , wherein the algorithm further comprises a non-linear least squares algorithm to estimate the parameters A 0 , A T , A k , and Φ k , where (k=1, . . . , M) solving the objective function S which is expressed as:
S
=
∑
j
(
p
i
j
-
A
0
j
)
-
∑
k
=
1
M
A
k
sin
(
ω
k
t
i
+
Φ
k
)
,
wherein the subscript i denotes distinct measurement times by applying the non-linear least squares algorithm whereby the objective function S is minimized by varying A and Φ.
4. The method of claim 2 , estimating the harmonic tide-related pressure variations in the algorithm with a combination of asynchronous pressure signals generated by all pressure sensors.
5. The method of claim 1 , wherein monitoring non-vertical movements of the seafloor by measuring distances between the pressure sensors at selected intervals of time throughout the prolonged period of time(t).
6. The method of claim 5 , wherein measuring the distances by a time of flight measurement of wireless signals transmitted by a wireless signal transmitter connected to one of the pressure sensors to wireless signal receivers connected to each of the other pressure sensors.
7. The method of claim 6 , wherein the wireless signals comprise acoustic signals.
8. The method of claim 7 , wherein the wireless signals comprise electromagnetic and/or photonic signals.
9. The method of claim 1 , wherein the pressure sensors are mounted on tripods which are mounted on or at least partly penetrate into the seafloor.
10. The method of claim 1 , wherein monitoring seafloor movements above a hydrocarbon containing formation from which hydrocarbons are produced.
11. The method of claim 10 , wherein monitoring vertical and horizontal seafloor movements above the hydrocarbon containing formation and managing, optimizing and/or otherwise controlling the production of hydrocarbons from the formation based on the vertical and horizontal seafloor movements.
12. The method of claim 11 , wherein monitoring contraction and/or expansion of the hydrocarbon containing formation in a geomechanical reservoir model based on the monitored seafloor movements.
13. The method of claim 12 , wherein providing data from the geomechanical reservoir model as input to a mathematical reservoir model and calculating the flux of hydrocarbon and other fluids through the hydrocarbon containing formation with the mathematical model, and managing, optimizing and controlling of the production of hydrocarbon fluid from and/or the injection of production stimulation fluids into the hydrocarbon containing formation based on the mathematical reservoir model.
14. The method of claim 6 , wherein the wireless signal transmitter and wireless signal receivers are mounted on tripods which are mounted on or at least partly penetrate into the seafloor.
15. The method of claim 14 , wherein the pressure sensors are mounted on the tripods.