Inferred production rates of a rod pumped well from surface and pump card information
View Patent ↗A method for inferring production of a rod pumped well. Inferred production is estimated in a well manager which not only performs pump-off control with a down-hole pump card, but also estimates liquid (oil-water) and gas production using the subsurface pump as a meter. Methods are incorporated in the well manager for identifying and quantifying several conditions: pump leakage, unanchored tubing, free gas and oil shrinkage. Quantifying such conditions in the well manger enables accurate inferring of production thereby eliminating the need for traditional well tests.
1. A method for managing production of a rod pumped well by using a subsurface pump ( 44 ) as a meter comprising the steps of,
generating a down hole pump card ( 212 ) from surface load and position measurements ( 208 , 210 ) of a rod pumping unit ( 10 ),
determining a position of traveling valve (TV) opening ( 214 ) from said down hole pump card;
determining from said down hole pump card a stroke distance S n ( 232 ) traveled by said plunger from said position of TV opening to a bottom of the stroke,
determining the volume of free gas ΔV gas ( 220 ) remaining in the pump at TV opening,
determining a distance S gas ( 222 ) of the stroke distance S n that corresponds to the volume of free gas ΔV gas remaining in the pump at TV opening,
determining a distance S l ( 224 ) of the stroke distance that corresponds to the liquid stroke distance in the pump at TV opening from the equation, S l =S n −S gas ,
determining net liquid production ( 226 ) at pump pressure and temperature for said pumping cycle from the equation,
Δ
V
1
=
π
4
d
2
S
l
where
ΔV 1 is net liquid production measured in cubic dimension at the pump,
d is the diameter of the pump measured in length dimension, and
S l is measured at the pump in length dimension,
converting ΔV l ( 228 ) at pump conditions to stock tank conditions, and
producing a report of liquid production of said well ( 230 ).
2. The method of claim 1 further comprising the steps of
identifying fluid load L f (lbs) ( 214 ), gross pump stroke S g (inches) ( 214 ), and tubing stretch S t (inches) ( 204 ) in addition to said net pump stroke S n (inches) from said pump card,
determining leakage in equivalent inches of stroke ( 216 ),
S
leakage
=
stroke
(
inches
)
=
bpd
0.1166
(
d
2
)
SPM
where
S leakage =pump stroke lost by pump leakage
SPM=pumping speed, stroke per minute
bpd=volume production lost by pump leakage, barrels per day
determining adjusted gross stroke ( 218 ),
S g adj =S g −S t −S leakage ,
iteratively solving a pump intake pressure equation ( 206 ),
P
i
=
P
a
-
L
f
A
p
where,
P i =pump intake pressure
P a =pressure above the pump plunger due to tubing head pressure and hydrostatic effects of oil-gas-water in the tubing
L f =fluid load derived from pump card
A p =area of plunger
by
(a) first assuming a low-trial P i , P i start ( 300 ),
(b) calculating an oil shrinkage factor F shrinkage and the gas remaining in solution (SCF/bbl of oil) at P i-start ( 302 ),
(c) computing the distance S gas using gas laws based on P i start pressure ( 318 ),
(d) computing S l ( 316 ) from
S l =S n −S gas ,
(e) determining oil cut at pump conditions ( 320 ) from shrinkage factor F shrinkage and measured oil cut at surface conditions,
(f) determining BOPD and BWPD at P i start ( 322 ) using oil cut at pump conditions, S l and
pump
stroke
=
bpd
0.1166
(
d
2
)
(
SPM
)
(g) determining free gas equivalent stroke ( 304 ),
S free gas =S g adj −S l ,
(h) determining dissolved gas volume (SCF/day) ( 326 ) at P i start using BOPD and gas remaining in solution,
(i) determining total gas (SCF/day) ( 306 ) passing through the pump into tubing by adding free gas volume to dissolved gas volume,
(j) determining tubing Gas Liquid Ratio, GLR, ( 308 ) from
GLR
=
total
gas
BOPD
+
BWPD
,
(k) determining P a start from said GLR ( 310 ),
(l) determining P a cal ( 311 ) from said pump intake pressure equation,
P
a
cal
=
P
i
start
+
L
f
A
P
(m) determining if P a start =P a cal ( 312 ),
(n) if so, P i n =P i start ( 328 ), if not, increasing P i start ( 314 ) and repeating steps (b) through (m) with P i n
where P i n is an nth iteration until
P a cal =P a n , and
P i true is equal to P i n ,
(o) determining ΔV gas ( 220 ) from P i true , and
(p) determining said S gas ( 222 ) from ΔV gas from,
Δ
V
gas
=
π
4
d
2
S
gas
where ΔV gas is measured in cubic dimensions at pump conditions
d is the diameter of the pump measured in length dimensions
S gas is measured in length dimensions.
3. The method of claim 1 further comprising the step of calculating inferred daily liquid production rate ( 228 ) in barrels per day from the equation,
R
IP
=
8.905
∑
Δ
V
I
T
P
+
T
d
where
R IP is inferred daily production rate in barrels per day at stock tank conditions
T P is the cumulative producing time in a day
T d is the cumulative down time in a day, if any,
and each ΔV 1 corresponds to a known instantaneous intake pressure P i .
4. The method of claim 3 further comprising the step of determining
daily free gas rate ( 200 ) in standard cubic dimension per day is determined from the equation
G
IP
free
=
50
T
p
+
T
d
(
P
i
P
s
)
(
z
s
z
i
)
(
T
s
T
i
)
∑
Δ
V
gas
where P i , z i , T i are pressure, compressibility and temperature at pump intake conditions,
P s , z s , T s are pressure, compressibility and temperature at standard conditions, and
ΔV gas is measured on each stroke of the pump while instantaneous P i is known, in standard cubic dimensions.
5. The method of claim 1 further comprising the steps of determining Traveling Valve (TV)/plunger leakage L TV rate ( 202 ) for said pumping cycle, and
determining net liquid production ( 227 ) from the equation
Δ V net =ΔV l −( L TV )( T )
where T is the cycle time of said pumping cycle.
6. The method of claim 5 wherein said step of determining Traveling Valve/plunger leakage L TV for said pumping cycle is derived by finding V crit by observing an increase in pump velocity ( 406 ) from said pump card and from the equation ( 408 ),
L TV =6.99 d 2 C p V crit
where
C p is a coefficient derived from the pump card
d is the pump diameter measured in length dimension, and
V crit is the pump velocity at standing valve opening measured in velocity dimension, and
L TV is leakage rate of the TV/plunger assembly in BPD.
7. The method of claim 5 wherein,
said step of determining Traveling Valve/plunger leakage L TV for said pumping cycle is determined by the substeps of
observing the rod string slowing down ( 428 ) and determining L TV ( 412 ) from the equation
L TV =6.99 d 2 C p V crit
where
C p is a coefficient derived from the position curve
d is the pump diameter is measured in length dimension
V crit is the pump velocity at standing valve closing.
8. The method of claim 5 wherein,
said step of determining Traveling Valve/plunger leakage L TV for said pumping cycle is determined by the substeps of
observing a maximum load loss rate of the traveling valve ( 432 ), and
determining L TV ( 434 ) from the equation
L
TV
=
6.99
d
2
C
p
k
rt
(
ⅆ
F
ⅆ
t
)
max
where
L TV is the leakage rate of the TV/plunger assembly
k rt is the combined stretch constant for the rod string and unanchored tubing and
(
ⅆ
F
ⅆ
t
)
max
is the maximum rate of traveling valve load loss (lb/sec).
9. The method of claim 8 wherein standing valve leakage is determined ( 436 ) from the surface load curve, and the equation
L
SV
=
6.99
d
2
(
1
-
C
P
)
K
rt
(
ⅆ
F
ⅆ
t
)
max
where
(
ⅆ
F
ⅆ
t
)
max
is the maximum rate of traveling valve load increase
(
lb
sec
)
.
10. A method for managing a rod pumped well by using the subsurface pump ( 44 ) as a meter comprising the steps of,
generating a down hole pump card ( 212 ) from surface load and position measurements ( 208 , 210 ) of a rod pumping unit ( 10 ),
determining the gross stroke S g ( 214 ) of the plunger of the subsurface pump ( 44 ) which pumps oil, water and gas to the surface via a production tube, where gross stroke S g is the distance measured from the lowest position where the Traveling Valve TV closes to the highest position where the standing valve SV closes,
identifying a characteristic of unanchored tubing by determining a distance S t ( 204 ) between TV closure to SV opening on said pump card,
determining a distance S n ( 232 ) as the distance traveled by the pump from TV opening to the bottom of the stroke from the equation
S n −S g −S t ,
determining liquid production for said pumping cycle ( 226 ) from the equation
Δ
V
l
=
π
4
d
2
S
l
,
where
ΔV l is measured in cubic dimension
d is the diameter of the pump measured in length dimension, and
S l is measured in length dimension, and
producing a report of liquid production of said well ( 230 ).
11. A method for managing a rod pumped well by using the subsurface pump ( 44 ) as a meter comprising the steps of,
generating a down hole pump card ( 212 ) from surface load and position measurements ( 208 , 210 ) of a rod pumping unit ( 10 ),
determining the gross stroke S g ( 214 ) of the plunger of the subsurface pump ( 44 ) which pumps oil, water and gas to the surface via a production tube, where gross stroke S G is the distance measured from the position where the traveling valve TV closes to the position where the standing valve SV closes,
determining fluid load ( 214 ) from said pump card,
determining tubing stretch ( 204 ) from the equation
S
t
=
K
L
f
D
p
E
t
A
t
where
S t is tubing stretch in length dimension
K is a dimensional constant
L f is fluid load in lb
D p is the pump setting depth in length dimension
E t is the modulus of elasticity of the tubing (Psi)
A t is the cross sectional area of the tubing (area dimension),
determining a distance S n ( 232 ) as the distance traveled by the pump from TV opening to the bottom of the stroke from the equation,
S n =S g −S t ,
determining liquid production ( 226 ) for said pumping cycle from the equation
Δ
V
l
=
π
4
d
2
S
l
,
where
ΔV l is measured in cubic dimension
d is the diameter of the pump measured in length dimension,
S l is measured in length dimension, and
producing a report of liquid production of said well ( 230 ).
12. A method for managing a rod pumped well by using the subsurface pump ( 44 ) as a meter comprising the steps of,
generating a down hole pump card ( 212 ) from surface load and position measurements ( 208 , 210 ) of a rod pumping unit ( 10 ),
determining the position of traveling valve (TV) opening ( 214 ) of said pump from said down hole pump card,
determining the distance S l ( 224 ) of the stroke distance of said pump that corresponds to the liquid stroke in the pump at TV opening,
determining traveling valve (TV)/plunger leakage L TV rate ( 202 ) for said pumping cycle,
determining liquid production ( 226 ) for said pumping cycle from the equation
Δ
V
l
=
π
4
d
2
S
l
where
ΔV l is measured in cubic dimension
d is the diameter of the pump measured in length dimension,
S l is measured in length dimension,
determining net liquid production ( 227 ),
Δ V net =ΔV l −L TV ( T )
where T is the cycle time of said pumping cycle, and
producing a report of liquid production of said well ( 230 ).
13. The method of claim 12 further comprising the step of inferring daily liquid production rate ( 228 ) in barrels per day from the equation,
R
IP
=
8.905
∑
Δ
V
l
T
P
+
T
d
where R IP is inferred daily production rate in barrels per day, and
T p is the cumulative producing time in a day, T d is the cumulative down time in a day, if any.