GYDA: Recovery of Difficult Reserves by Flexible Development and Conventional Reservoir Management

Abstract

Gyda is a 200MMstb field, located in the North Sea Central Trough, offshore Norway. The field was discovered in 1980, and first oil was produced in 1990. It is one of the deepest, hottest and poorest quality oilfields in the North Sea. The structurally complex field contains three different fluid types, and the crude is asphaltene rich. The shallow marine sandstone reservoir is gently dipping, wedge-shaped, with an oil column of 500m. The field receives no aquifer support and is being developed by waterflood. The connate water/injection water mix has a severe scaling tendency.Development of the field is set against a background of tight cost control within the industry generally, and within the Operating company in particular. With six wells drilled per year, a current offtake rate of 70Mstbpd, and areas of the field showing early mature performance, the challenge is to maintain production whilst keeping costs low. The development is therefore managed by maintaining maximum flexibility in drilling locations, sequence and well use, by use of appropriate technology, and by the innovative use of conventional techniques to exploit the field's characteristics. This paper describes: 1. reservoir complexity; 2. the technologies employed to meet the reservoir management challenges; 3. development philosophy; 4. field management history; and 5. value generation.

Petroleum geology features and research developments of hydrocarbon accumulation in deep petroliferous basins

“…The genesis of deep-buried high-quality reservoirs mainly includes dissolution by organic acids (Surdam et al 1984), effects of hydrocarbon charging and deep thermal fluids (Navon et al 1988), clay mineral membranes (Ehrenberg 1993;Dolbier 2001), temperature and depth (Ezat 1997), faulting (Moretti et al 2002), abnormal pressure (Wilkinson et al 1997;Osborne and Swarbrick 1999), effects of fractures (Harris and Bustin 2002), sedimentary environment (Amthor and Okkerman 1998;Khidir and Catuneanu 2003;Pape et al 2005;Rossi et al 2001), and tectonics (Watkinson and Ward 2006). Preservation mechanisms mainly include early hydrocarbon charging (Gluyas et al 1990;Robinson and Gluyas 1992;Rothwell et al 1993), grain coating (Heald and Larese 1974;Ramm et al 1997), and overpressure (Ramm et al 1997;Osborne and Swarbrick 1999). Geothermal gradient, °C/100m Fig.…”

The Effect of Grain-Coating Microquartz on Preservation of Reservoir Porosity

“…The reservoirs of both fields are Upper Jurassic shallow-marine sandstones, with the Gyda Sandstone in the Gyda field and the Ula Sandstone in the Ula field (Spencer et al, 1986;Home, 1987). The Gyda Sandstone reservoir is relatively deep (3650-4165 m), hot (155°C at 4155 m), and overpressured (605 bar) (Rothwell et al, 1993). The Ula Sandstone is located at a depth of 3400-3800 m, with a reservoir temperature of 143°C and a pressure of 483 bars at 3450 m (Spencer et al, 1986;Home, 1987).…”

“…The Ula Sandstone is located at a depth of 3400-3800 m, with a reservoir temperature of 143°C and a pressure of 483 bars at 3450 m (Spencer et al, 1986;Home, 1987). The Upper Jurassic sandstones are predominantly fine and medium grained, moderately well sorted, relatively homogeneous, and variably argillaceous, and were deposited in offshore marine-shelf settings (Brown et al, 1992;Rothwell et al, 1993). The thickness of the Upper Jurassic section varies considerably as a result of erosion during the middle-late Volgian, and also as a result of differential subsidence.…”

“…Diagenetic quartz cementation is commonly regarded as the most important porosity-reducing process at depths greater than 2500 m (Bjørlykke et al, 1992;Giles et al, 1992), and anomalously high porosity and permeability values in deeply buried sandstones commonly have been explained by early hydrocarbon trapping in the reservoir (e.g., Selley, 1978;Sommer, 1978;Gluyas, 1985;Gluyas et al, 1990Gluyas et al, , 1993Robinson and Gluyas, 1992b;Burley, 1993;Rothwell et al, 1993) or highly overpressured sandstones (Bjørlykke et al, 1989(Bjørlykke et al, , 1992Ramm and Forsberg, 1991;Ramm, 1992;Ramm and Bjørlykke, 1994). High-quality sandstones in the Gyda and Ula fields commonly have been explained by early hydrocarbon trapping (Bjørnseth and Gluyas, 1991;Rothwell et al, 1993); however, Giles et al (1992), Ramm (1994), and Walderhaug (1994a) concluded that there was no relationship between the presence of hydrocarbons and high porosities. Walderhaug (1994b) also concluded that there was no relationship between overpressure and the amount of quartz cement, and Bjørkum (1984Bjørkum ( , 1994Bjørkum ( , 1996 showed that the dissolution of quartz is not a pressure-driven process.…”