doing more with less - unconventional
TRANSCRIPT
DOING MORE WITH LESS -
UNCONVENTIONAL
Russell Gray - Total E&P UK Ltd.
Tushar Patil - BHGE
THE CHALLENGE
● Determining pressures in tight formations above and below reservoir
intervals is critical information to define the pore pressure gradient
● Defines the drilling window
● Defines the well architecture
● Pore pressure estimated by models often lack definition of over
pressure ramps with limited tie in points (LOT, FIT)
● Requirement to define the pore pressure in the Cretaceous to
Kimmeridge Formations in very low porosity and permeability matrix
to constrain drilling windows.
CHALLENGES OF PRESSURE TESTING IN VERY
LOW MOBILITY FORMATIONS
● Issues with supercharging - Low volume
extraction
● High drawdown – Pre test rate &
volume dependency
● Slow build-up times - Tool storage/ Poor
stability / Poor repeatability
● Accurate Mobility calculation
Pre
ssure
Distance Away from
Wellbore
Flushed Virgin
Pres
PSC
RATE DEPENDENCY
PR
ES
SU
RE
TIME
Flo
wli
ne
de
co
mp
ressio
n
Pretest duration
Longer storage
dominated early
time build-up
Late time formation
response
Low Mobility Pretest
PR
ES
SU
RE
TIME
Flo
wli
ne
de
co
mp
res
sio
n
Pretest duration
Steady State Flow
(formation flow =
drawdown rate)
Storage
dominated
early time
build-upLate time formation
response
High Mobility Pretest
Fluid Flow Rate =
Drawdown Rate Rate
Fluid Flow Rate < Drawdown
RateRate
TIMETIME
PRESSURE TESTERS – THE OPTIONS
• Straddle packer tools
Long time to obtain a test and even longer for sampling.
Swabbing potential.
Limited life span – some reinforced straddle packers are good for ~6 tests.
High stuck in hole potential.
• Recent developments of large face probes available for formation testers
Increase surface area for testing.
Reduce time for pre tests.
More tests per run and significantly lower risk of stuck tools.
• FTeX new generation formation tester
Small internal tool volume.
Very precise and capable of very low rate drawdown.
Smart drawdown control.
PRESSURE TESTERS – TOOL AND PROBE SELECTION
FTeX:
0.1 psi/min RCX with XXR:
0.91 psi/min
FTeX vs XXR Overlay at Same Depth - FTeX Faster PBU at 0.008mD/cP
FTeX & XXR Overlay
FRA mobility: 0.008 mD/cP
- FTeX
- XXR
Efficiency – more data in less time (reduced rig time)
More confidence in data
TIME
PR
ES
SU
RE
FTEX: LARGER TEST AREA – FURTHER IMPROVEMENT
IN EFFICIENCY
Stability 1.8 psi/min
TIME TAKEN FOR TEST IS HALVED
BY INCREASING PROBE AREA.
Stability 0.91 psi/min
Stability 1.8 psi/min
Mobility = 0.003 mD/cP
37 tests (30 dry) in
13 hours with the
Standard packer
34 tests (18 dry) in
18 hours with the
Elongated packer
Straddle packer 4 tests (3 uncertain) 25 hours
XXR probe 16 tests in 18 hours
TIME
PR
ES
SU
RE
Volu
me
VALIDATION
8
Drawdown
pump
Isolation Valve
Quartz Gauge
Probe
Time since end of drawdown (s)
Theoretical Flow Regimes + Build Up Derivative Analysis
Spherical Radial
0.01
0.1
1
10
100
0.01 0.1 1 10 100 1000 10000
Radial
Spherical
Tool Storage
Slope = 1
Pre
ss
ure
dif
fere
nc
e a
nd
Deri
va
tive
(p
sia
)
Log-log plot
Skin effect
Probe type tools do not develop a
real radial flow, since pressure
transient lines propagate around the
wellbore. During a pressure test ,
only a few cc is drawn from
formation.
• Real time during the test evaluation and post job
• Using both linear and derivative plots.
• Mobility from Flow Rate Analysis –FRA (Area under methods tend to over estimate mobility – particularly in lower mobilities)
VALIDATION OF DATA
AREA UNDER METHOD FOR MOBILITY (SPE115825)
Shape factor is a function of
the tool geometry.
An error in the determination of
pretest volume will transform
linearly to an error in mobility
Time
Pre
ssu
re
Fluid Flow Rate
Pre
ssu
re
Slope
FORMATION RATE ANALYSIS (FRA)
DRAWDOWN MOBILITY MEDIUM/HIGH PERMEABILITY
CASEP
RE
SS
UR
E
Fluid Flow Rate =
Drawdown Rate
MAX RATE – DRAWDOWN MOBILITY
LOW PERMEABILITY
● Stable Pressure
● Drawdown Mobility Equation
k/μ = C * rate
● Rate
- Piston Rate (DDR)
- Fluid Flow Rate (FR)
DDR
FR
(Pf – Pmin)
Fluid Flow Rate vs Piston Rate
C = Constant, depends on probe
DD Rate Mobility 2.9 mD/cP vs Fluid Flow Rate Mobility 1.8 mD/cP
PRESSURE TEST – LOW PERMEABILITY
Pre
ssu
re
Dra
w D
ow
n R
ate
1st DD 2nd DD 3rd DD
Very precise control of drawdown rate allows
tool to monitor formation fluid flow = faster tests
INVERSE - RATE & VOLUME TO PRESSURE: SMART
TOOL
LOW MOBILITY TEST
Time
Formation flow rate
Pre
ssure
P
ressure
Efficiency factors:
• Pre job planning (tool selection /
probe selection)
• Real time job monitoring
• Minimum two draw downs
• Real time validation and QC –
ensure seeing formation response
not tool storage / static filtration
• Team work
• Experience
DOING MORE WITH LESS - CONCLUSION
• More pressure tests in less time and with considerably lower risk (probe
over packer tools)
• Valid pressures in very low mobility formations where no previous data
was possible
• Significant reduction in uncertainty in pore pressure prediction
• More accurate mobility calculations