This paper presents a case of cluster well development in swamp wetland in high pressure salt gypsum formation of N.A Oilfield of Iran and analyzes the advantages and challenges of cluster drilling and completion. Experience and lessons learned from cluster drilling and completion are issued.

The major challenges of cluster drilling and completion is anti-collision and higher torque and drag in three dimensional trajectory well. The cluster drilling and completion is more difficult due to the existence of high pressure salt gypsum with high pressure salt water in N.A Oilfield. This paper presents well trajectory optimization design, anti-collision design and technical treatment to decrease drag and torque in three dimensional trajectory well for cluster wells in N.A Oilfield. The above mentioned cluster drilling technology has been used in more than 50 wells in N.A Oilfield and solve the three dimensional trajectory well drilling and completion difficulties such as drill string stuck, casing stuck and so on.

The key technology of the cluster well is trajectory design and control to drill a smooth hole and decrease collision. The completed wells show that the duration of three dimensional trajectory well is 10 days longer than that of the two dimensional trajectory well for 3D trajectory is more difficult for drilling, running casing, completion, acidizing due to higher torque and drag. So the composite cost of the three dimensional trajectory well is 1 million dollars more than that of the two dimensional trajectory well. It is economically feasible to use three dimensional cluster well for the cost of construction of one pad is about 3-4 million dollars in the swamp wetland surface conditions. The technical difficulties and economic evaluation shall be considered in the design of cluster well development and not all the cluster well drilling is economically feasible.

Cluster well is a practical and economic development mode in offshore oil production, offshore oil on the land and some harsh surface conditions such as swamp. Considering the complexity and cost of drilling three dimensional trajectory well, it is recommended to design two dimensional trajectory well in cluster well deployment if there is no limitation in the land surface condition.

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