The Brenda field development: a multi-disciplinary approach

Ian F. Jones, Rod Christensen, Jamie haynes, John Faragher, Ika Novianti, Henry Morris, and Giles Pickering show how a multi-disciplinary combination of modern processing, imaging and inversion techniques can identify overlooked hydrocarbon prospects. Recent initiatives in the North Sea and UKCS such as the introduction of the Fallow Field initiative and offering of Promote licences have started to generate activity by attracting new entrants who can provide new capital and new ideas to focus on exploration and appraisal. Fields which had been abandoned, or considered of insufficient commercial interest, have been offered a new lease of life by allowing proactive companies to identify and exploit latent commercial prospects by tying in to existing infrastructure. Here, we showcase one such recent discovery, made by Oilexco, where a multi-disciplinary approach was taken to identify potential targets using state-of-the-art pre-processing and high resolution velocity model building and pre-stack imaging, combined with detailed calibrated reservoir attribute analysis based on elastic impedance inversion. This field could prove to be one of the largest finds in the North Sea for three years. Introduction Oilexco’s UK North Sea drilling programme on Licence P1042 (Block 15/25b) in the Outer Moray Firth, targeted oil in the Paleocene Upper Balmoral sandstone. Initially three wells were proposed: one on the structure previously drilled by the 15/25b-3 well, one on a structural high with classic four-way closure, and one on a channel sand feature, whose prospectivity was indicated by an anomalously low elastic impedance (EI) response on the far-offset stack. The surface location of the first new well, 15/25b-6 is approximately 150 m west of Conoco’s 15/25b-3 undeveloped discovery, which tested 2690 b/d of 39o oil from the Upper Balmoral sandstone from 20 ft of net pay in 1990. The 15/25b-6 well encountered the Brenda oil find announced by Oilexco on 26 January 2004. The well intersected a series of oil-bearing Paleocene Upper Balmoral sands, the thickest of which has 26 ft of high quality oil pay. In addition to this sand, several other thin bedded oil bearing sands were also intersected. The entire section was tested and yielded 40o API oil from the Upper Balmoral sandstone at an average rate of 2980 b/d, over an 18-hour test under stable flowing conditions, from 56 ft of perforations (evaluated with open-hole wire-line logs and formation fluid sampling tools). Associated natural gas flowed at an average rate of 600 million ft3/d throughout the test. No water or sand was produced during the test period. The surface location of the second well (15/25b-7) is approximately 4 km northwest of 15/25b-6. The vertical hole encountered ~ 50 ft of good quality Upper Balmoral sand which was logged as water bearing. The side-track (15/25b- 7Z) encountered another very porous clean Paleocene Upper Balmoral sand with a thin oil column at the top of the sand and a mud log gas response. The results of the well suggest that the Sheryl structure is separate from the Brenda oil accumulation which is at a structurally lower position. As a consequence, the well was abandoned. The third well, (15/25b-8) targeted the low EI anomaly. It was located 0.50 km west of the 15/25b-6 well, acting as an appraisal well to the Brenda oil accumulation. The well encountered 69ft of high quality oil pay in the Upper Balmoral sand, and also tested 40o API oil, but at rates up to 4785 b/d.