Abstract

A real time data link has been employed recently on the Ula Field (Norway), with new data loaded directly to the subsurface database. The data were used to assist in the optimal placement of two geosteered wells. Onshore staff were therefore able to participate fully in the steering process, focusing on rapid data interpretation rather than data management. Well results were highly positive.

Introduction

Ula is a mature waterflooded oil-field in block 7/12 (licence PL19a) of the Norwegian sector of the North Sea (Fig. 1), operated by BP Norge AS on behalf of partners Svenska Petroleum AS and DONG Norge AS. The oil accumulation is moderately deep (3350–3800 m TVDSS) and hot (150 deg C). The reservoir consists of upper Jurassic shallow marine sediments (Ref. 1) in a 4-way dip closure above a salt structure (Ref. 2) (Fig. 2). The field was first discovered in 1976, and first oil was produced in 1986. Plateau oil production of between 100 to 150 mbd was maintained until late 1993. Production over the last 5 years has been between c. 25 mbd, sustained by infill drilling in the upper unit 1A reservoir, and by injecting water and gas. A water-alternating gas (WAG) scheme has recently commenced.

This paper describes recent experience on the last two unit 1A infill wells, which were geosteered, near-horizontal wells on the crest of the field structure. During the drilling of these wells, a real time data link connected the Ula platform with BP's offices in Stavanger. This link enabled data from a directional drilling / LWD vendor and a mudlogging company to be loaded directly into BP's corporate subsurface database on a regular and automatic basis. The drilling and LWD data were also made available for the entire drilling and completions team through use of a web-based browser.

The real time loading of trajectory, mudlog and loggingwhile- drilling data enabled the onshore team to assist the offshore geosteering specialists in the optimal placement of the borehole. The real time link ensured that offshore data was available close to 24 hours a day in the office, updated typically every few minutes. This allowed the onshore team to be involved in the geosteering process on a frequent basis. The onshore focus was on interpretation of new data within the seismic volumes and the 3D surface model. The onshore team were able, therefore, to advise the team offshore in a timely fashion of the optimal placement of the wellbore, having rapidly interpreted the newly-acquired drilling data in a 3D context.

Ula Reservoir Background

The Ula reservoir is a shallow marine reservoir of Upper Jurassic age, similar to the nearby Gyda and Tambar Fields and the Fulmar Field (Ref. 3) in the UKCS. The stratigraphic framework and reservoir layering scheme are described in Fig. 3 (Ref. 4). The majority of the reservoir layers are present over the entire field area, as a result of being deposited in a shallow marine setting with minimal syn-depostional faulting. The Upper Jurassic shallow marine depositional system responded to changes in relative sea-level and sediment supply by first prograding (unit 3), then retrograding (unit 2B), then prograding (unit 2A) before finally retrograding (unit 1)(Ref. 5). The water depth finally rose at the end of the Jurassic, covering the reservoir by deeper marine mudstones of the Farsund and Mandal Formations (Fig. 3), with the latter being the source rock (Ref. 6). Intervals of high / low reservoir quality can be traced over a significant distances, with little evidence for lateral facies changes. This facilitates using geosteering techniques to maximise well productivity.

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