depth, the limestone-dominated formation has dolomite streaks containing significant amounts of entrapped gas. Surface facilities were limited in the amount of gas that could be handled to a gas/oil ratio (GOR) of 440 m3/m3 [2,500 ft3/bbl]. Any stimulation to initiate flow in the well had to avoid gas production and keep the GOR below this limit by minimizing stimulation of the dolomite streaks.
Kepong/ Tiong/Bekok
MALAYSIA Kerteh Kuala Lumpur Tiong
Gas Oil
Singapore Bekok 0 0m 100
km 100 i
> Tiong field. The offshore Tiong field is located 260 km [162 mi] off the coast of central Malaysia. This sandstone field covers an area of about 20 km2 [7.7 mi2] and, along with nearby Kepong and Bekok fields, produces oil and associated gas (inset bottom). These fields send oil and gas by pipeline to a gathering point at Kerteh on the mainland. From Kerteh, oil and gas are sent by pipeline to Kuala Lumpur, Singapore and other processing facilities (not shown).
Kepong
A chelant from the HACA family was the obvious choice for the stimulation job. Chelants in the HACA group exhibit enhanced reaction rates with limestone and more limited reaction with dolomites—an important factor for the success of this treatment due to the entrapped gas. A treatment plan for this well was developed using the Schlumberger StimCADE software for acid placement. This plan called for using coiled tubing to place an HACA chelant into a narrow zone of the limestone matrix at 2,620 m. The software predicted a 1.5-m radial pene tration by the HACA chelant.
50,000 100,000 150,000 200,000 250,000 300,000 350,000 400,000
0 January 2007 April 2007 June 2007
> Tiong field stimulation results. The OneSTEP procedure performed on the Tiong well in April 2007 had immediate positive results from the chelant treatment. Oil production increased from about 16 m3/d [101 bbl/d] to more than 70 m3/d [440 bbl/d]. Similarly, gas production increased from less than 20,000 m3/d [0.7 MMcf/d] to about 85,000 m3/d [3 MMcf/d].
Oil flow Gas flow
10 20 30 40 50 60 70 80
0
Stimulation treatment was carried out without incident. A preflush of a solvent mixed with water preceded the chelant to aid flowback by making the formation water-wet. Treatment pressure averaged 8.3 MPa [1,200 psi], and the chelating injection rate was 0.056 m3/min [0.35 bbl/min]. After treatment was complete, the operator displaced the well with diesel and pulled the coiled tubing. Positive results from the treatment with the chelant were immediately apparent. Oil production increased from the initial nonflowing state to 96 m3/d [600 bbl/d]. This oil production increase was accompanied by a GOR increase of only 264 to 299 m3/m3 [1,500 to 1,700 ft3/bbl]—well within the operator’s limits. Results from these cases confirm that chelants are useful for stimulation of hot carbonate reservoirs. This capability is also present for sandstones.
Acidizing High-Temperature Sandstone Wells A West African well drilled in 1984 typifies the choices an operator must make when confront - ing the need for acidizing a high-temperature sandstone formation.24
This well, completed at a
depth of 2,360 m [7,743 ft] in a deltaic sandstone formation with 15% carbonates, had a bottomhole temperature of 128°C [263°F]. During a nearly 20-year period, oil production had declined from 490 m3/d [2,500 bbl/d] to 224 m3/d [1,408 bbl/d] with a corresponding increase in water output. The water, first noted in 1991, had increased to 30% by 2003. The effect of the water on comple - tion equipment had been observed during a prior
60
Oilfield Review
Gas flow, m3/d
Oil flow, m3/d
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