Characterization of lithology and reservoir rock for deep gas drilling in Siljan Impact Structure, Sweden

Conference · Fri Jan 01 00:00:00 EST 1988

OSTI ID:6678143

Castano, J R; Sneider, R M; Bolger, G W

The Gravberg 1 well in the Siljan impact structure in Sweden has been drilled entirely in granite and dolerite intrusions of Precambrian age to a present depth of 6.6 km. Study of the cuttings at the well site included a lithologic description, with emphasis on quantifying mineralogical, textural, and pore-space parameters that affect porosity and permeability and that can indicate the potential presence of a fractured reservoir. Important mineral parameters are epidote, reddish feldspar, chlorite, and other alteration products. Textural parameters include the presence of fractures, cataclastic and brecciated graikns, vugs, and drusy crystals. Although rare, the presence of drusy crystals clearly shows that open fractures are present. The study is also geared to identify minerals that affect wireline logs (e.g., alteration products such as chlorite,sericite, and illite, and heavy minerals such as pyritic and magnetite4). Cuttings examination is crucial as relatively few cores or sidewalls have been recovered. Laboratory studies incorporating capillary pressure tests, SEM, and thin-section petrography (in polarized and fluorescent light) reveal that the samples contain a bimodal pore structure composed of larger pores representing the microfractures and smaller pores representing the intercrystalline microporosity developed within altered grains. Porosity in the granites averages 0.96% (typical Swedish granite is 0.5%), and the permeability is 0.003-0.027 md.

• OSTI ID: 6678143
• Report Number(s): CONF-880301-
• Resource Relation: Conference: Annual meeting of the American Association of Petroleum Geologists, Houston, TX, USA, 20 Mar 1988
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
36 MATERIALS SCIENCE
NATURAL GAS DEPOSITS
GEOPHYSICS
RESERVOIR ROCK
LITHOLOGY
SWEDEN
DOLOMITE
EXPLORATION
FRACTURED RESERVOIRS
GRANITES
MICROSTRUCTURE
MINERALOGY
PERMEABILITY
PETROGRAPHY
POROSITY
PRECAMBRIAN ERA
SCANNING ELECTRON MICROSCOPY
STRUCTURAL CHEMICAL ANALYSIS
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CRYSTAL STRUCTURE
ELECTRON MICROSCOPY
EUROPE
GEOLOGIC AGES
GEOLOGIC DEPOSITS
IGNEOUS ROCKS
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MICROSCOPY
MINERAL RESOURCES
MINERALS
OXYGEN COMPOUNDS
PLUTONIC ROCKS
RESOURCES
ROCKS
SCANDINAVIA
WESTERN EUROPE
030200* - Natural Gas- Reserves
Geology
& Exploration
360602 - Other Materials- Structure & Phase Studies