Drilling Engineering Association
Project Proposal
DEA #113 – Phase 2
“Drilling Gumbo Shale – A Study of
Environmentally Acceptable Muds to
Eliminate Shale Hydration and Related
Borehole Problems”
Some Aspects of Non-Aqueous Drilling Fluids
•
•
•
•
• Advantages
Can prevent problems caused by hydration of
shale, such as drill-string balling and borehole
instability.
Can provide excellent filtration control, lubricity and
stability at high temperatures.
• Disadvantages
Can result in excessive loss of mud because of low
fracture extension pressures.
Are subject to stringent environmental regulations,
and can result in costly liabilities.
Limitations of Commonly Used Laboratory
Tests of Shale Hydration
• Inadequate procedures such as swelling and
dispersion tests utilizing unconfined, unstressed
shale.
• Use of weathered shale core, cuttings or particles
containing air or water vapor in the exposed pore
spaces.
• Exposure of shale to muds at ambient temperature.
Unique Features of the
OGS Downhole Simulation Cell
• Preserved downhole shale core can be restored to in
situ stresses and temperature prior to being drilled
with the drilling fluid to be studied.
• Artifacts, such as air in shale pore spaces or
introduction of an arbitrary simulated pore fluid, can
be avoided.
• Fluid transfer between drilling fluid and shale can be
measured.
• Effects of drilling fluid on shale strength and stability
can be observed.
• Changes in shale composition can be observed.
Downhole Simulation Cell System Components
Downhole Simulation Cell Cross Section
Downhole Simulation Cell
Reports of Prior DSC Studies of Pleistocene
Shale from the Gulf of Mexico
• Gas Research Institute report, “Effects of Drilling
Fluid/ Shale Interactions on Shale Hydration and
Instability,” GRI 99/0213.
• Drilling Engineering Association Project #113 report,
“Drilling Gumbo Shale – A Study of Environmentally
Acceptable Muds to Eliminate Shale Hydration and
Related Borehole Problems.”
• Both reports are available from the OGS Laboratory,
Inc. website: www.ogslab.com .
Differential Pressure
• The differential between the borehole pressure and
the formation pore pressure is a driving force
affecting transfer of fluid from drilling mud to shale.
• Raising mud weight can contribute to shale hydration.
Chemical Osmosis
• Chemical osmosis is a driving force determined by
the relative water activities of the drilling mud and the
shale pore fluid at downhole conditions.
• Water tends to escape from a dilute solution (higher
water activity) to a more concentrated solution (lower
water activity).
• The chemical osmotic force and resulting transfer of
fluid is dependent upon the efficiency of the
semipermeable membrane at the drilling mud/shale
interface in blocking passage of ions and molecules
while allowing water molecules to pass.
Diffusion Osmosis
• Diffusion osmosis is determined by the differences in the
concentrations of the individual solutes in the drilling mud
and in the shale pore fluid. Ions and molecules of each
species tend to move from the high to low concentration.
• The flow of solute and associated water is dependent
upon the solute selectivity of the drilling mud/shale
interface at downhole conditions for each individual solute.
• When using a water-based mud, diffusion osmosis
opposes chemical osmosis. A lightly compacted shale
having large pore throats favors diffusion osmosis, while a
more compacted shale favors chemical osmosis.
Importance of Drilling Mud / Shale Membrane
• Non-aqueous based muds (diesel, mineral, synthetic)
can provide an ideal semipermeable membrane that
prevents diffusion of ions and molecules, eliminating
diffusion osmosis.
• Water-based muds do not provide an ideal semipermeable membrane. Even if chemical osmosis
predominates and is extracting water from a shale,
diffusion osmosis can cause solutes from waterbased mud to invade the shale and create instability.
Company Sponsors of DEA #113 – Phase 1
Amoco Prod. Co.
Arco E&P Tech.
Baker Hughes Inteq
Baroid Drlg. Fluids
Chevron Pet. Tech.
Exxon Prod. Res.
Gas Research Ins.
M-I Drlg. Fluids
Mobil E&P Tech.
National Silicates
Newpark Drlg. Fluids
Schlumberger Tech.
Shell E&P Tech.
Texaco E&P Tech.
Unocal Tech. & Oper.
Criteria for Muds to be Tested in DEA #113
• Environmentally suitable for discharge in U.S. waters
of the Gulf of Mexico
• Mud characteristics such as rheology, filtration
control, temperature stability and suspension of
weighting material suitable for drilling in the Gulf of
Mexico
• Mud to contain 20 lb/bbl of ground Pierre shale as
simulated drill solids
Parameters for DEA #113 DSC Tests
of Gulf of Mexico Pleistocene Shale
Axial Stress
Confining (Horizontal) Stress
Sandpack (Pore) Pressure
Borehole (Drilling Fluid) Pressure
Shale Temperature
Drilling Fluid Temperature
3,450 psi
2,650 psi
2,000 psi
2,000 or
2,200 psi
150 °F
Drilling
120 °F
Circulating 150 °F
(Sandpack fluid: Chloride solution having water activity of 0.89 and
cations in the same ratios as the cations in the exchange sites of the shale)
Fresh-Water Lignosulfonate
Water Activity of Drilling Fluid
Fluid Transfer into Shale, mL/hr
Relative Shale Stability, psi
1.00
0.85
1,500
Distance from
Borehole Surface
1/8” ½”
1–¼” Initial
Shale Moisture, % 29
20
15
12
Shale Hardness
0
0
20
90
Fresh-Water Lignosulfonate
Potassium / Lime
Water Activity of Drilling Fluid
Fluid Transfer into Shale, mL/hr
Relative Shale Stability, psi
1.00
1.20
1,550
Distance from
Borehole Surface
1/8” ½”
1–¼” Initial
Shale Moisture, % 25
14
14
12
Shale Hardness
30 30
30
90
Potassium / Lime
Synthetic
Water Activity of Drilling Fluid
0.74
Fluid Transfer into Shale, mL/hr -0.40
Relative Shale Stability, psi
2,000
Distance from
Borehole Surface
1/8” ½”
1–¼” Initial
Shale Moisture, % 16
13
12
11
Shale Hardness
0
55
55
90
Synthetic
Guidance for DEA #113 – Phase 2
• Only one water-based mud in Phase 1 was
successful in extracting fluid from the Gulf of
Mexico Pleistocene Shale
• Two muds having similar compositions
allowed hydration and weakening of the shale
• Technical Representatives of Sponsors of
Phase 1 identified several mud compositions
that warranted further study
DEA #113 – Phase 2
• Preserved downhole Pleistocene shale core from the
Gulf of Mexico is available for further DSC studies.
• Each company participating in Phase 2 can select a
mud composition for DSC testing.
• Cost of DEA #113 – Phase 2 is $20,000.
• Five Sponsors are required to initiate the program
and work can begin as early as April, 2002.
• Deliverables are comparisons of mud performance
under the best laboratory evaluation procedures
available to the industry.