US 12,460,520 B2
Controller for suppressing slugs in petroleum production systems
Dinart Duarte Braga, Vitoria (BR)
Assigned to PETROLEO BRASILEIRO S.A.—PETROBRAS, Rio de Janeiro (BR)
Appl. No. 17/761,001
Filed by PETROLEO BRASILEIRO S.A.—PETROBRAS, Rio de Janeiro (BR)
PCT Filed Sep. 15, 2020, PCT No. PCT/BR2020/050365
§ 371(c)(1), (2) Date Mar. 16, 2022,
PCT Pub. No. WO2021/051178, PCT Pub. Date Mar. 25, 2021.
Claims priority of application No. BR 102019019350-6 (BR), filed on Sep. 17, 2019.
Prior Publication US 2022/0349281 A1, Nov. 3, 2022
Int. Cl. E21B 43/12 (2006.01); E21B 34/16 (2006.01)
CPC E21B 43/12 (2013.01) [E21B 34/16 (2013.01)] 14 Claims
OG exemplary drawing
 
1. A slug-suppressing controller, comprising a fuzzy inference system (FIS) hybridized with a classic Proportional-Integral-Derivative (PID) controller to control a choke valve of an oil production system,
wherein the slug-suppressing controller further comprises a block to estimate a severity of the slugging, and
wherein the block to estimate the severity of the slugging is based on determining a frequency of oscillation based on the following algorithm:
a. sampling an actual value of measured variable X(n), adding it to a buffer having a size L;
b. calculating an average of the buffer X(1:L), storing it in X;
c. determining a sequence of average zero, X0(1:L), using equation: X0(1:L)=X(1:L)−X;
d. calculating a variance of X0(1:L); if it is less than a threshold of σ2min, the oil production system is considered to be stable and the algorithm returns an oscillation frequency of zero;
e. calculating self-correlation for X(1:L), storing it in XX(1:L);
f. determining an index i of the element pertaining to XX(1:L), which has the greater value after the first crossover of zero;
g. calculating a period of oscillation Tg from the second equation, in which Ta is the sampling time:
Tg=Ta(i−1); and
h. returning a value of the oscillation frequency in mHz, calculated as 1000/Tg.