Reservoir sandstones, significance

Bloch S. (1994) Secondary porosity in sandstones significance, origin, relationship to subaerial unconformities, and effect on predrill reservoir quality prediction. In Reservoir Quality Assessment and Prediction in Clastic Rocks (ed. M. D. Wilson). Society for Sedimentary Geology (SEPM), vol. 30, pp. 137-159. 

Macaulay C. I., Fallick A. E., McLaughlin O. M., Haszeldine R. S., and Person M. J. (1998) The significance of dl3C of carbonate cements in reservoir sandstones a regional perspective from the Jurassic of the northern North Sea. In Carbonate Cementation in Sandstones (ed. S. Morad). International Association of Sedimentologists, Oxford, vol. 26,pp. 395-408. 

The significance of of carbonate cements in reservoir sandstones a regional perspective from the Jurassic of the northern North Sea... 

With a few exceptions reservoir rocks are sediments. The two main categories are siliciclastic rocks, usually referred to as elastics or sandstones , and carbonate rocks. Most reservoirs in the Gulf of Mexico and the North Sea are contained in a clastic depositional environment many of the giant fields of the Middle East are contained in carbonate rocks. Before looking at the significance of depositional environments for the production process let us investigate some of the main characteristics of both categories. 

In this sandstone aquifer, the estimation of the C activity,, in the total dissolved carbon (TDC) to 100% of modern carbon is justified by the absence of carbonates in the reservoir and by the C contents in the TDC. A significant relation could be determined between the C activity in the TDC and C = —7.7Si3 — 59.6%. This gradual en-... 

Fracturing and fault compartmentalization of sandstones fundamentally affects reservoir properties and may significantly influence the fluid migration pathways in a basin (Knipe, 1993). Open fractures may form high-permeability conduits, whereas cement-sealed fractures form barriers to fluid flow. Seismic, petrophysical and reservoir performance data allow regional (field-scale) effects of faulting on fluid flow to be constrained. However, much fracturing and associated cementation may occur at sub-... 

Energy dispersive X-ray analysis (EDXA) is of assistance in identifying the principal chemical elements in particular crystals. This information, along with crystal shape, enables one to identify reasonably well the minerals likely to be contacted by a surfactant slug when injected into a core or a reservoir formation. Thus, the basic sand matrix of these materials is revealed while the presence of particular clay minerals, such as kaolinite, can be seen in Berea sandstone and Glenn Sand dolomite appears to be present in significant amounts in the core from the San Andres formation. 

Table I shows some statistics on the types of reservoir subjected to enhanced recovery operations. Most EOR projects in Canada, particularly hydrocarbon-miscible projects, are being conducted in carbonate reservoirs, and hydrocarbon injection in the United States is mostly in sandstones. As will be evident from this chapter, the type of reservoir rock is of significance to surfactant propagation during foam-flooding.

Electrophoretic mobilities of quartz and clays, both isolated from Berea sandstone, and of calcite and dolomite in three different brines are shown as a function of pH in Figure 9 (74). These results are unique in that they were obtained with brines of higher ionic strength than are usually used in the measurement of solid surface charge. All three brines have the same ionic strength (0.406 mol/L) but differ in composition. The reservoir brine contains significant levels of divalent cations, which are mostly Ca2+. Electrophoretic mobilities at pH 7, also taken from reference 74, are listed in Table VI. 

CO2 was injected in the EFU 40 well above and below the calcite-cemented layers, but the previous producing wells, EFU 39 and 41, had no perforations in the Ramsey I sandstone below the calcite layers. The CO2 that was produced in the EFU 41R well probably represents banked-up energy that gave a first flush of CO2 when the well was completed. CO2 injected below the calcite-cemented layers in well EFU 40 became trapped, resulting in significantly higher reservoir pressure (energy). The CO2 could not dissipate to other portions of the reservoir, and there was no production below the cemented layers. 

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