Water production in northeast Syria has increased significantly in recent
years. As a result, costs per barrel of oil have increased and the field’s
production is currently constrained by the facilities capacity.
Production logging tool (PLT) surveys, combined with a reservoir study,
showed that good-quality sands were not properly swept by the water, probably
because of poor connectivity in the reservoir. It was anticipated that
these unswept sands could contribute to production if the watered-out sands
were shut off.
A newly developed gel/cement has been used to shut off the watered-out sands
in a cost-effective manner. The gel/cement system combines the properties
of two shutoff techniques:
• Cement for mechanically strong perforation shutoff.
• Gel for excellent matrix shutoff.
The gel, used as “mix water” of the cement, will be squeezed into the
matrix, creating a shallow matrix shutoff. The cement will remain in the
perforation tunnel as a rigid seal. This system showed superior shutoff
performance in the laboratory compared to normal cement squeeze techniques.
Selective perforation of the hydrocarbon zones will re-establish the oil
production. The shutoff zones can be reopened later in the well’s life when
artificial lift has been installed.
The system was tested in the field in two wells. In the first field trial,
84 m of perforations (gross) was squeezed off with the gel/cement in a single
attempt. After reperforation of the top and the middle zone, the well produced
at a strongly reduced water cut (i.e., 25 to 33% compared with 60 to 62% before
the treatment) and an increased oil production (i.e., 3,000 BOPD compared with
1,000 BOPD before the treatment). The oil production declined to 2,000 BOPD
over a year; the water cut gradually increased over that period to 56%. In the
second well, full shutoff was achieved but oil production could not be resumed
for reasons that are not fully understood.
Waterdrive, either natural or through water injection, is probably the most
important recovery mechanism for oil production from oil-bearing rocks. In
a layered reservoir, this will cause water breakthrough in the
high-permeability layers, leaving oil behind in the unswept layers. Generally,
oil production decreases with the maturity of an asset while the water
production increases. For 1999, the worldwide daily water production
associated with oil production has been reported as 33 million m3 or, roughly,
3 bbl of water for every barrel of oil (Bailey et al. 2000). The U.S. petroleum
industry generates 2.4 billion m3 of water annually (Sustainable Development
2004). This amounts to an average 7 to 8 bbl of water per 1 bbl of
oil. Water production within the one group has roughly increased from
350,000 m3/d in 1990 to more than 1,000,000 m3/d today (Khatib and Verbeek
The costs associated with handling produced water are typically proportional
to the amount of water produced. Consequently, costs per barrel of oil
produced continue to increase with increasing water
production. Ultimately, individual wells or complete fields are abandoned
when cash flows turn negative because of excessive water production.
The heterogeneous geologic nature of most oil reservoirs, however, provides
opportunities to prevent or reduce excessive water production. In layered
reservoirs with good vertical isolation between the layers, water production
can be managed either by controlling the injection profile in the injectors (if
water is injected) and/or by selectively producing different layers in the
producers. It is essential that the well integrity and cement bond are good to
prevent communication behind pipe and casing.
© 2006. Society of Petroleum Engineers
View full textPDF
- Original manuscript received:
8 December 2004
- Revised manuscript received:
13 June 2005
- Manuscript approved:
15 June 2005
- Version of record:
20 May 2006