Case Study: Horizontal Well Campaign Increases Production 280% and Eliminates Production Decline Rate for CNOOC

PeriScope mapper and EcoScope service enable precise well placement for exploitation of remaining reservoirs in mature fields

Challenge: Drill horizontal well program to access thin oil-column attic reserves and unproduced thin laminated reservoirs in mature reservoirs with declining production rates.

Solution: Geosteer lateral drain placement using PeriScope bed boundary mapper and real-time images from EcoScope multifunction LWD service.


  • Successfully drilled five horizontal wells within the target zones.
  • Achieved average 3,180 bbl/d initial production per well and 1% water cut, overshooting set targets by 280%.
  • Reduced the production decline rate from 15 to 0%.

Developing a mature oil field experiencing production decline

Chinese National Offshore Oil Corporation (CNOOC) had developed highly mature oil fields in the XiJiang block offshore South China, which produced for 17 years before starting to show signs of production decline at the rate of 15%. CNOOC decided to execute a horizontal well program to access and exploit the remaining undeveloped marginal reservoirs of the field. The main targets of the new development campaign were the thin oil column attic reserves as well as the unproduced thin laminated reservoirs in the area. The primary objective of this operation was to reduce the production decline rate of the field and to ultimately increase the oil reserve recovery.

Since the reservoir targets were much thinner compared with original drilling conditions, the standoff between lateral sections and oil/water contact was very sensitive to well performance and reserve recovery. Precise landing and lateral placement of the horizontal wells was critical to the success of the campaign.

Using LWD for landing and lateral section placement

Schlumberger recommended a complex suite of LWD services for accurate horizontal placement in the thin sands, channel sands, and thin oil column reservoirs with strong bottom-water. The BHA would include EcoScope multifunction LWD service for real-time formation evaluation and structural dip interpretation using density images and PeriScope bed boundary mapper for distance-to-boundary measurements. The PeriScope service provided deep azimuthal measurements for geosteering, giving drillers the ability to delineate multiple boundaries simultaneously. Along with these LWD services, the BHA would incorporate a rotary steerable system to maintain directional control in the demanding horizontal sections.

Increasing production 280%, eliminating production decline

EcoScope and PeriScope services delivered consistent and high-quality data that enabled the CNOOC and Schlumberger teams to drill five horizontal wells in the target zones. The horizontal well campaign achieved an average 3,180 bbl/d initial production per well and 1% water cut. This production rate is 280% higher than set targets. During this new horizontal well campaign in XiJiang oil field, the production decline rate of the fields was reduced from 15 to 0%.

Download: Horizontal Well Campaign Increases Production 280% and Eliminates Production Decline Rate for CNOOC (1.24 MB PDF)

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Geosteering Service Hits Targets, Halts Production Decline

XiJiang fields showed a 0% production decline rate as a result of the horizontal well campaign.The well trajectory was successfully placed within the thin channel sand target despite finding the actual structural profile differed significantly from the predrill model.
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"The applications of EcoScope service and PeriScope mapper for well placement ... enabled the team to make effective real-time decisions for placing the trajectory in the best place to drain the remaining hydrocarbon and to keep the trajectory away from the OWC."
Gao Xiao Fei
Chief G&G
CNOOC XiJiang, South China

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