Mud Temperature Effects on Lost Returns

1
Mud Temperature Effects on Lost Returns

• For Deepwater Wells

2
Original Concept
3
Temperature Effects on Borehole

• Higher borehole temperatures (from hot drilling
  fluids) will cause the rock to try to expand.
• Since it cannot expand outward it tries to expand
  radially and towards the inside of the borehole.
• Since it cannot expand, the hoop stress level in
  the rock will increase.
• This higher stress will increase the rocks
  resistance to fracture.

4
Temperature Effects on Borehole
Another way to look at the effect is with an
established crack in the borehole. The higher
temperature will act to close any existing cracks
and increase the pressure needed to open the
fracture.

• Above is an unheated simulated borehole (at STP)
  with a fracture 0.10 wide.

At left is the borehole (that has been heated)
closing the fracture.
5
Increasing the Drilling Window
Or in-other-words, not let the bore-hole get
weaker due to the cooling of the rock by the
circulating mud.
The seawater (and mud in the riser) at the
mudline will cool-down to very low temperatures
when not circulating. It averages anywhere from
32 to 36 F.
6
Lost Returns Problems

• The lost return problems are seen in many
  different worldwide operations. Among these are
• Deep Water wells
• Areas with high geothermal formation temperatures
• Steam flood operations
• Drilling through naturally fractured formations

7
Production Field Data
This chart shows how the injection pressure
dropped 400 psi (on a fractured water disposal
well) when the temperature dropped 17 degrees F
from 78F to 61F. From SPE paper 52738 (Joe
Schmidt)
8
Temperature Effects on Borehole

• This effect has been well known in
  stimulation/production operations.
• The higher the temperature of fracturing fluids,
  the harder it is to breakdown a formation.
• Thomas Perkins and Jay Gonzalez published an SPE
  paper (SPE 10080) in October 1981 where they
  said
• This paper gives examples which illustrate the
  effect of injecting a large volume of liquid
  which is cooler than the in situ reservoir, as is
  common when waterflooding. The cooling can have a
  large effect on lateral earth stresses, and for
  some conditions vertical hydraulic fracturing
  pressures can be significantly reduced.

9
More Documentation

• SPE 25732. " predicts an increase of the actual
  LOT value at the shoe when deepening the hole,
  with respect to the measurements made at the
  beginning of the drilling phase.
• SPE 71366. States that " the breakdown mud weight
  decreases by .03 ppg for every 1 deg centigrade
  of cooling of a vertical well."
• SPE 29428. Says " Borehole stress evaluation
  shows how the near well-bore fracture gradient
  can be exceeded, when cooling is combined with
  ECD."

10
The Well Test

• Guerrera 90

11
Test Well Procedure

• Circulate the well (Guerrera 90) by the 13-3/8
  shoe at 3000 with muds at different
  temperatures (90F, 130F, 150F)
• We used an electric line to record the downhole
  temperature and pressures during circulation and
  LOT.
• We used 45,000 lbs of crushed ice to lower the
  pit temperatures from 115F to 75F. We circulated
  the mud until we achieved a BHT of 90F.
• We used two hot oil trucks to increase the
  downhole circulating mud temperature from 90F to
  130F and 150F
• We Performed an LOT test (at each temperature) to
  determine near breakdown pressure.

12
Well Test Results

• We tested 81 of shale and sand sequence on the
  test well. We obtained the following results
• Surface mud pit temperatures can be managed and
  controlled
• Increasing the BHT significantly increases the
  Leak-Off Test (LOT) effective mud weight.
• This effect was quantified. A 1.0 ppg increase
  for a change in BHT of 61F.
• We tested using downhole temp and pressure gauges
  at 92F, 133F, and 153F.

13
Well Test Results
LOT 16.2
LOT 15.2
LOT 16.0
14
Test Well
Mud Pits
15
Test Well
Mud pits and ice blower hose
Ice and crushers
16
Test Well
Hot oil truck Two trucks heated 100 bbls from 80F
to 150F in 45 minutes
17
Historical Data InDeepwater
18
Well 1
Bottom of salt
Lost returns
19
Well 2
Bottom of salt
Lost returns
20
Cementing
21
Frac Gradient Plus For Cementing
Current Technique cools down formation and causes
the cement to frac away early
Circulating mud down DP (inside liner) will heat
formation and add 200 psi resistance to fracturing
Now an additional 2500 of cement column can be
placed before fracturing occurs
Increase in Cement height
Mud Circulation
Cement
Lost returns
22
Frac Gradient Plus For cementingModeling Tahiti
South
Heating and then cementing the 10-1/8, 79 ppf,
Q125 liner in 12-1/4 hole
23
Circulating Hot MudsResults in a total formation
temperature increase of 50F