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Theory of Transgressive and Regressive Reef (Bioherm) Development and Origin of Oil

1950; American Association of Petroleum Geologists; Volume: 34; Linguagem: Inglês

10.1306/3d933ed8-16b1-11d7-8645000102c1865d

1558-9153

Theodore A. Link,

Hydrocarbon exploration and reservoir analysis

PART I The established geological principle of transgression and regression of epi-continental seas, the resultant sediments, and their fauna and flora, is applied to or bioherm-forming organisms. (Coral reef and are regarded as synonymous.) Bioherms which develop during a transgression are differentiated from those of a retreating sea by the associated sediments. A transgressive bioherm is surrounded and overlain by marine clastics deposited during submergence, while the regressive type of bioherm is associated with evaporites and/or other types of sediments deposited during withdrawal of the sea. PART II It is suggested that hydrocarbons found within or bioherm reservoirs are indigenous, because of the obvious concentration and accumulation of organisms in them. The porosity and permeability of or bioherm reservoirs are attributed not only to the hollow corallites et cetera, but also to the helter-skelter accumulation of them so that, in many instances, such porosity is greater, more effective, and more continuous. Partial or entire obliteration of porosity is, in part, due to infiltration of evaporites associated with the regressive type of bioherm. DEFINITION OF TERMS BIOHERM AND BIOSTROME A is an accumulation of the secreted hard parts of sessile types of primitive invertebrates and plants such as corals, bryozoans, crinoids, sponges, algae, et cetera, which accumulation is greater than the surrounding contemporaneously deposited sediments, thus giving rise to mounds, ridges, or reefs. Therefore, coral-reefs and are, in a sense, one and the same. According to what organism predominated to cause it, such an accumulation is termed a coral-reef or coral bioherm; a bryozoan reef or bryozoan bioherm; an algal reef or algal bioherm, et cetera. When in doubt one should refer to them as or reefs without commitment as to composition. A is an accumulation of the same or similar sort of material as a or reef, but the accumulations are in layers or strata which are no greater in vertical dimensions than the contemporaneously deposited surrounding sediments. Obviously there is a gradation zone between biostromes and bioherms for, no matter how thin or how thick the accumulation may be, it pinches or lenses out somewhere, and thus any biostrome must be regarded as a lens even though it may be only 2 feet thick and 100 miles or more in areal extent. Also, it may have irregularities or humps on top of it, of varying sizes, which could be termed bioherms. One could, in a sense, look upon these primitive bioherm- or biostrome-forming organisms as catalysts in the sea which cause excessive precipit tion or concentration of carbonates from the sea-water wherever the environment is favorable.