Halfdan: Developing Non-Structurally Trapped Oil in North Sea Chalk

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMaersk Olie og Gas AS has as operator for the Danish Underground Consortium (DUC) discovered and initiated the development of the Halfdan accumulation located in the southern part of the Danish North Sea. The accumulation comprises oil and gas in a low permeability chalk reservoir located outside structural closure. This paper describes how the phased, fast track development of Halfdan was planned and executed while testing a new concept for constructing an aligned sweep pattern.Tilted oil-water and gas-oil contacts across the Halfdan area are indicative of non-equilibrium conditions. The nonstructural trapping in the Halfdan area is provided by a combination of up dip thinning of the hydrocarbon bearing section, late structural tilting and the slow re-adjustment caused by the low permeability.Accelerated a nd stepwise development was pursued to allow continuous optimisation of the development in light of the significant uncertainties associated with the fluid distribution and reservoir production characteristics. Appraisal drilling from a template and tie-back of the appraisal wells to temporary production facilities via the drilling rig and early deployed pipelines enabled production from the Halfdan 10 months after finalising the discovery well. Furthermore, a temporary water injection package installed on the drilling rig enabled evaluation of water injection before the installation of permanent facilities including determination of displacement efficiency, fracturing pressure and induced fracture orientation. Halfdan was produced through permanent facilities less than 18 months after finalising the discovery well.

Diagenetic characteristics of low permeability, non-reservoir chalks from the Central North Sea

“…Brasher and Vagle, 1996;D'Heur, 1984) and the chalk reservoirs of the Danish Sector (e.g. Albrechtsen et al, 2001). Alternatively vertical migration through the chalk could be largely through fractures, and is regarded as a crucial factor by many (e.g.…”

“…Hydrocarbons migrating through the chalk have also been trapped non-structurally by intra-chalk seals. Accumulations of this kind (such as the Halfdan Field- Albrechtsen et al, 2001;Megson and Tygesen, 2005) have recently been found and there is potential for others to exist. Such accumulations may be more common in a situation where the permeability structure of the chalk is lower than previously envisaged.…”

Rapid Determination of MIC in Oil Production Facilities with a DNA-based Diagnostic Kit

“…The Halfdan oil field (Jacobsen et al, 1999;Albrechtsen et al, 2001) is a chalk field with a permeability of 0.2-2 mD Water injection commenced in January 2001 from one injector, HDA-04. Injection seawater is supplied from the Dan FF platform via a 9 km long sub-sea pipeline.…”

Problems Caused by Microbes and Treatment Strategies The Effect of Nitrate Injection in Oil Reservoirs – Experience with Nitrate Injection in the Halfdan Oilfield

“…The Halfdan field is laterally extensive and comprises a high porosity (25-30%), low permeability (0.5-2 mD) chalk reservoir located outside structural closure (Albrechtsen et al, 2001). The producing horizon is the Maastrichtian Age Chalk with a reservoir temperature and pressure of typically 80 • C and 4,200 psi, respectively.…”