Mary L. Barrett

Landscape Modification of the Smackover Field, Arkansas

ABSTRACT The Smackover oil field in south central Arkansas remains the largest oil field in Arkansas. In the early to middle 1920s it was one of the biggest oil fields in the United States. With such success came oil field waste and land destruction. This study characterizes the landscape modification and healing that has occurred in the Smackover Field since the years of peak production. Aerial photography from 1936 and 1996 was used to study landscape change. The major features mapped were earthen storage pits and associated landscape scars. The pits held millions of barrels of oil and unwanted saltwater, which commonly leaked into drainage areas. GIS software was used to evaluate pit distribution through time. Digital mapping allowed for quick comparison of surface topography and drainage plus production distribution. Two types of pits were defined: active pits and scars. Intact pits were areas that still held the basic shape of the original pit. Scars were defined as areas that were leveled out, but retained the basic shape of the original pit due to a lack of vegetation. A variety of comparisons can be made from two sets of photographs. The areas of the pits and scars in 1936 and 1996 were compared to determine the percent of reduction of the pits and vegetative healing that has occurred over 60 years. The distribution of scars has a direct relationship to the density of wells in the field. Areas where the well sites are denser produce more scars and pits.

Predicting the Permeability of Unconsolidated Sediments From Grain Size Measurements

ABSTRACT Laser diffraction particle size measurements are shown to be superior to porosity-permeability correlations in predicting the permeability of unconsolidated samples. For slightly laminated, deep water, Plio-Pleistocene, medium silt to very fine-grained sand samples from an offshore Louisiana well, there are good correlations between the grain size parameters and measured permeability. Although the permeabilities calculated from the Krumbein and Berg equations are well correlated with permeability, the Carman-Kozeny equation is preferred because it comes the closest to a one-to-one fit. For samples with significant laminations, a good fit between measured and calculated permeability was obtained by modifying the Carman-Kozeny equation for the proportional amount of the coarser layers. For samples with median grain diameters of 90 microns or less (very fine-grained sand) sieve analysis does not adequately resolve the grain size for prediction of permeability.

Distribution of Thermal Maturity in Central Graben, North Sea: ABSTRACT

The distribution of oil and gas fields in the northern North Sea closely reflects the structural patterns of Mesozoic-graben development. Late Mesozoic-Tertiary basin subsidence in the Central Graben has resulted in a very favorable burial history for source rock maturation. Time-stratigraphic information and present-day average temperature gradients were used from several wells to calculate depths of oil and gas windows in the area. By intersecting this depth-to-generation trend with the Late Jurassic-Cretaceous unconformity surface, the resulting map view reflects thermal maturation at this structural level plus the underlying Kimmeridge Clay. Average depths to the onset of moderate hydrocarbon generation range from 8000 to 10,000 ft (2.438 to 3048 m). A combination of rapid sedimentation and sufficient subsurface temperatures in the Central graben promoted early source rock maturity as compared with the northern North Sea as a whole. The absolute timing of oil generation could in part be dependent on the magnitude of paleotemperature changes possibly associated with thermal subsidence of the basin. Early oil generation and migration may have promoted preservation of high chalk porosities as discussed in published works on the Ekofisk area.