Dumbarton Field, UKCS: Rapid Redevelopment of a Complex, Mature North Sea Asset Using New Rotary-Steerable and Geosteering Technologies

摘要

The Dumbarton Field, operated by Maersk Oil North Sea in Block 15/20 has a number of drilling and well placement challenges, which hampered development during the 80's and 90's when operated by the previous owner. These include formation instability, directional-drilling control issues and thin complex reservoirs which are poorly imaged on seismic. Reservoir overburden is fast drilling formations with hard stringers. The field pore-pressure gradient is at 9.07ppg EMW but mud density needed for wellbore stability is greater than 11.6ppg. This resultant high overbalance and other issues such as hole cleaning, complex directional profile, ECD management at high ROPs, can lead to inefficient motor drilling. The soft formations also create limitations for push-the-bit rotary steerable systems to deliver the required directional performance to land wells. To overcome these drilling challenges a new point-the-bit, rotary steerable system with a high dogleg capability has been utilised for successful landing of these wells into reservoir sections without need for pilot holes or mechanical sidetracks. Additionally a new LWD tool that allows monitoring of the distance and direction to formation boundaries up to 15 ft away from the wellbore has been used to proactively guide the wells along the thin oil reservoir units/sands. These tools also enabled the wells to be placed as close to the reservoir roof shales as possible to maximize stand-off from the waterleg and hence increase overall oil recovery. Distance and direction to boundary data displays are intuitive to interpretation allowing better geosteering decisions without compromising ROP and drilling efficiency. Within six months six wells were delivered including three sidetracks (One top hole and two horizontal sections). All wells penetrated more reservoir sand than prognosed and all were drilled faster than prognosed. Initial production testing was higher than expectation.