English Edition (6 MB pdf) - Saudi Aramco

tractor. The result is that the gripper element will not slip
under the maximum load of the tractor’s exertion. Retraction
of the gripper element is accomplished with redundant fail-safe
springs, ensuring that the elements return to their non-energized
state in all situations when the pump pressure falls below the
threshold value.
The operational walking sequence is as follows: Expand the
forward gripper; direct the cylinders to move inward toward
the CA, thereby forcing the forward tractor downhole;
collapse the forward gripper then expand the aft gripper;
direct the cylinders to move outward toward the tool joints,
again forcing the tractor downhole; and finally collapse the aft
gripper. This cycle repeats itself, producing a walking process
that continues until the load on the tractor is sufficient to stall
the tractor or the pressure differential is lowered below the
start valve pressure threshold, stopping the tractor.
HEALTH, SAFETY AND ENVIRONMENT (HSE)
The main concern related to the HSE aspects of the project
involved the high concentration of H 2 S observed in the Manifa
field, which could reach 10 wt% or 1,000 parts per million
(ppm). During the project execution a significant number of
personnel were expected in the area, performing tasks at
different sites from road construction to operating the drilling
rigs. The operator had identified areas of potential H 2 S releases
and put in place monitoring devices at designated zones of
maximum H 2 S concentration (10 ppm and 3 ppm zones).
The stimulation of the water injection wells was planned with
zero flow back strategy. No pressure bleed-off at the surface was
allowed to take place throughout the entire operation.
The H 2 S concern was also addressed through the use of H 2 S
scavengers. First, several H 2 S scavengers were extensively tested
to select the type and the concentration required to protect the
completions and the CT pipe during the entire intervention.
Second, the pump schedule was designed to include a large
volume of preflush fluids containing the H 2 S scavenger. During
the logging run, the injection of the treated water would help to
further reduce the risk of having H 2 S at surface.
JOB OPERATION
The generic program for the intervention in the Manifa field
wells could be summarized as:
1. Rig up.
2. Pressure test.
3. Slick line run.
4. Injection test (optional).
5. CT run to perform stimulation:
• Deployment of BHA and tractor.
• RIH and tractor operation to reach TD.
• Spot stimulation fluids while pull out of hole (POOH)
in alternated stages of preflush, acid and diverter.
• POOH and pressure retrieve BHA and tractor.
6 SUMMER 2010 SAUDI ARAMCO JOURNAL OF TECHNOLOGY
6. CT run with MPLT:
• Deployment of BHA and tractor.
• RIH and perform tractor operation to reach TD.
• Perform logging passes.
• POOH and pressure retrieve BHA.
7. Slick line run with gauges.
8. Injection test 10,000 barrels per day (bpd) at maximum
2,200 psi for 2 days.
9. Four days falloff test with downhole gauges in the well.
Table 3 shows the amount of fluids used for the treatment
in each well.
Well 1 (Deepest Well)
The TD of the well was 28,257 ft with 6,038 ft open hole
completed with 7” tubing. The objective was to increase the
injection rate of this well up to 10,000 bpm with a maximum
pressure of 2,200 psi. Since there was no record of
interventions in such ERWs in open hole, the operator set a
conservative goal for the CT to reach far enough to cover
50% of the open hole section.
A pre-stimulation injection test was done and showed that
the well could only take 1,750 bbl/day of water with wellhead
pressure (WHP) reaching up to 2,200 psi. The initial
simulation showed that without the aid of friction reducer or
a tractor, the CT would lock-up at 16,900 ft. A first attempt
to RIH with the tractor was aborted due to a failure with a
release valve in the CA of the tractor. In a second run, the CT
locked up at 22,200 ft. A pull test was performed and the
tractor was activated observing an increase of 8,000 lbs in the
CT weight, Figs. 4 and 5. The tractor pulled the CT without
interruption at an average speed of 10 ft/min to reach TD at
28,257 ft. At TD, the tractor was de-activated to reduce the
pressure drop at the BHA and maximize the pumping rate.
Over 1,500 bbls of acid fluid stages were then pumped and
injected in the formation as the CT was POOH.
After reaching the TD and completely pumping the acid
treatment fluid, a post-injection test was done to evaluate the
stimulation effectiveness and understand the well performance.
Fig. 4. Simulation of CT lock-up in Well 1.