Shallow Heavy-Oil Deposit in a Pennsylvanian Fluvial Sandstone Reservoir, Eastburn Field, Missouri
Published:January 01, 1987
J. F. Weber , Jr., W. J. Ebanks, 1987. "Shallow Heavy-Oil Deposit in a Pennsylvanian Fluvial Sandstone Reservoir, Eastburn Field, Missouri", Exploration for Heavy Crude Oil and Natural Bitumen, Richard F. Meyer
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Eastburn field/ Vernon County, Missouri, produces heavy, 21° API, crude oil at a depth of 33 m (110 ft) from a thin, 6-9 m (20-30 ft), sandstone stratigraphic trap in the Cherokee Group of middle Pennsylvanian age. Sedimentary structures, grain size trends, geometry of the sandstone, and the nature of associated sediments indicate the fluvio-deltaic origin of the reservoir.
Development drilling at very close spacing, 60 m (200 ft) between wells, provided information from which a sedimentologic model of porosity and permeability distribution in the Eastburn field reservoir could be developed early in project life. From this model, strategies were proposed that guided further drilling and completion of wells, extension of the field, and placement of production facilities. Development drilling guided by the fluvial sandstone model resulted in tripling the known volume of the heavy-oil resource, with a minimum number of dry development wells being drilled.
The reservoir sandstone is composed mostly of medium to very fine quartz sand, rock fragments, and mica, with abundant interstitial detrital silt and clay. Authigenic kaolinite clay and calcite and siderite cements reduce reservoir quality and contribute to problems in production, such as low injectivity of steam and exhaust gases in the thermal recovery process. Identification of the permeability-reducing minerals aided in design of well-stimulation treatments and contributed to increased productivity.
In a few cases, where contouring of the sandstone thickness was doubtful, production performance of individual wells provided additional data to guide the geologic interpretation. This synergistic approach helped to minimize the cost and maximize the efficiency of the field development.
Figures & Tables
Exploration for Heavy Crude Oil and Natural Bitumen
Gross volumes of oil, which must be kept in mind to address the volume/size framework, may be thought of in order from largest to probably smallest volumes as follows: (1) generated; (2) dissipated; (3) degraded/ partially preserved; and (4) trapped and conventionally producible. Basic knowledge of these volumes may be from greatest to least in essentially reverse order.
The 332 largest known accumulations (less than 1% of the total number) account for more than three-quarters of the known 7.6 trillion bbl of oil and heavy oil or tar in more than 40,000 accumulations in the world. About 2.4 trillion bbl of estimated undiscovered conventional oil added to the known volume of 7.6 trillion bbl yields a total of 10 trillion bbl known or reasonably estimated. World-wide cumulative production of about 500 billion bbl of oil accounts for only 5% of the gross.
Oil in place must be estimated for conventional oil fields before comparison with heavy oil and tar accumulations. The size range of accumulations considered in the size distribution of the 332 largest known accumulations is from 0.8 to 1850 billion bbl of oil. The smallest conventional fields in the distribution are about 1 billion bbl because the size cut-off is 0.5 billion bbl of oil recoverable. The size distribution of the 332 largest known accumulations approaches log normal and is overwhelmed by the largest three supergiant tar deposits that hold nearly half of the total 5495 billion bbl.
Globally, the largest three accumulations, all heavy oil or tar, are in South and North America; the two largest conventional oil fields are in the Middle East. Prudhoe Bay and East Texas fields rank 18 and 34, respectively, in descending size order.