Sedimentology and unexpected pressure decline: the HP/HT Kristin Field

Abstract

Since production began in the HP/HT Kristin Field off mid-Norway, reservoir pressure in each of the three mid to late Jurassic reservoir units (the Garn, Ile and Tofte formations) has declined significantly more rapidly than was initially predicted. In the Garn Formation, the Tofte Formation and to some extent also the Ile Formation, this has occurred at least partly because an unusual distribution of reservoir properties led to bias in the four-well appraisal dataset and this in turn resulted in an overestimation of reservoir properties. Of particular importance to this bias was the fact that very good but unrepresentative reservoir properties were encountered in all three reservoir zones in the discovery well located in the centre of the field. These, it is now realized, are not even typical of most of the central part of the field but are, instead, restricted within one, small, anomalous area. Study of cores and thin sections indicates that in each reservoir unit this directly reflects a concentration of more energetic depositional facies in the area while less energetic facies are present on three sides. This pattern was not predictable from the original dataset and seems to have arisen because there was structural control upon facies positioning during accumulation of the reservoir section. This influenced the distribution of cleaner, coarser grained, more proximal depositional facies and, ultimately, reservoir quality distribution and pressure development. What is interesting about Kristin Field is that the structural influence upon sedimentation is observed within the footwall stratigraphy of a major relay structure where the primary provenance direction was on the hanging-wall side. This pattern is the reverse of what is normally reported in tectono-stratigraphic studies.

The deep Møre and Vøring basins of the Norwegian Sea as basement highs prior to Late Jurassic rifting

“…11). Observations onshore East Greenland suggest a relatively narrow western branch of the seaway with the Liverpool Land peninsula as part of the eastern and emergent basement (Doré, 1992;Brekke et al, 2001;Surlyk, 2003;Quin et al, 2010). Lower and early Middle Jurassic, tide-dominated sand intervals have been described (Fig.…”

Structural geology and basin development of the Norwegian Sea

“…However, the origin, position and areal extent of suggested land areas are poorly constrained. A local source area, represented by an elongate island or a belt of islands, has been suggested (e.g., Doré 1992;Quin et al, 2010), whereas Ravnås et al (2014) regarded the Sklinna Ridge as the source for the coarse clastics. However, land areas with limited areal extent would have had small water catchments, unlikely to form large river deltas.…”

“…Assuming a basement high between the Halten Terrace and the basin onshore East Greenland, the seaway was situated to the east of, rather than along, a wide Jurassic rift-basin between East Greenland and the Norwegian mainland. Observations from the Jameson Land Basin on East Greenland, suggest a narrow branch of the Jurassic seaway to the west (Doré, 1992;Brekke et al, 2001;Surlyk, 2003;Quin et al, 2010). Within this basin, located west of the Liverpool Land peninsula, deposition of Early to Middle Jurassic, tide-dominated sand intervals have been described (e.g., Surlyk, 1991;Dam & Surlyk, 1992;Koppelhus & Dam, 2003;Surlyk, 2003).…”

Nanomaterial-Based Drilling Fluids for Exploitation of Unconventional Reservoirs: A Review

“…Kristin field contains gas condensate in three sandstones (lower to Middle Jurassic paralic sandstones). The average depth of gas condensate reservoir was 4600 m and 4850 m [158]. For Kristin Development Field, it was decided earlier that the weighting agent would be micron-sized barite (MBS).…”