Page 133 - The Petroleum System From Source to Trap

6. Siliciclastic Reserooir Rocks 127

paleolatitudinal belts as the many modem deserts of the sediment and organic matter (Eugster and Surdam, 1973;
world (McKee, 1979). When overlain by transgressive Eugster and Hardie, 1975; Hardie et al., 1978). Nearly all
marine black shales, eolian sands can form both carrier lakes are ephemeral features that are ultimately
beds along regional dip and reservoir rocks in structural converted to fluvial plains as the lake basin fills with
trap, such as the Rotliegendes of the North Sea (Glennie, sediment (Picard and High, 1981).
1 9 72, 1 9 8 2, 1 9 87) and the Tensleep Sandstone of The lacustrine-related sandstones of the Uinta basin of
Wyoming (Moore, 1984; Kocurek, 1988). Some very thick Utah, and particularly of basins in China, are prolific
eolian sands, such as the Jurassic Navajo and Wingate hydrocarbon reservoirs (Table 6.3). These reservoirs are
sandstones do not appear to have been regional carriers, associated with lakes in which large amounts of lipid­
in spite of their 1600-km lateral extent, because they were rich organic matter were preserved that commonly form
isolated in largely continental sequences of rocks without oil shales (surface) and generate waxy oils (subsurface).
regional seals or source rock connections. Only in the In the Uinta basin, the marginal lacustrine facies contain
Wyoming thrust belt where the lateral equivalent of the the principal reservoirs for hydrocarbons (Fouch and
Navajo Sandstone, the Nugget Sandstone, lies in thrust Dean, 1982; Fouch et al., Chapter 25, this volume). At
contact with a mature source rock do hydrocarbon accu­ Red Wash field in the eastern Uinta basin, the reservoir
mulations occur. In summary, although eolian sands sandstones are formed in lacustrine delta front bars,
represent a small percentage of the world's sedimentary fluvial channels, and shoreface strata that are interstrati­
record, where present they form important, thick reser­ fied with impermeable lacustrine and overbank clay­
voirs of clean, laterally extensive sandstone. stones. This results in poor vertical and lateral connec­
tivity of reservoirs and requires close well spacing to
maximize oil recovery.
LACUSTRINE-RELATED RESERVOIRS Information on the Chinese lake deposits and the
associated hydrocarbon accumulations has become more
The reservoir strata in or adjacent to a lacustrine available in the past two decades (Chen et al., 1980; Li et
setting are deposited by processes that occur in a deltaic al., 1988). Reservoirs in the Chinese deposits include
or shallow water setting and include delta mouth bars, turbidites, lacustrine bar, deltaic sediments (Meyerhoff
fluvial channels, shoreface sands, offshore bars, and even and Willums, 1976), and alluvial fans (Cheng, 1981).
lacustrine turbidites (Fouch and Dean, 1982). Descrip­ In summary, thick lacustrine deposits are relatively
tions of these kinds of deposits are found in the other rare in the stratigraphic record. They occur in continental
sections of this chapter. Sandy siliciclastics are concen­ basins that are commonly internally drained and flanked
trated around the margins of most lakes. However, as with alluvial sediments. The reservoir strata are formed
lake levels rise and fall, the shoreline facies extend by lake-marginal facies, such as deltas, bars, or channels,
landward or prograde into the lake forming cyclic and turbidites. Their proximity to deeper water source
packages that coarsen upward (Figure 6.3). Deeper water facies and to interbedded sealing shales makes them a
lacustrine strata, particularly in saline lakes, contain large good target for hydrocarbon exploration in large
amounts of both siliciclastic and carbonate fine-grained structures.

Table 6.3 ( co ntinued)
Reserves (BOE) Gas Migration
Recoverable In place or Oil Trap Sty lee Distance Depth Porosity Permeability
(x1Q9) (x109) Produced Type t> (km) (m) (%) (md) References
0.6 0 BI-A v 1 1 90-1300 30-32 500-2000 Chen and Wang, 1980

8.0 0 BI-A V? 1 0 97 Halbouty, 1 9 80
1
0.6 0 R/0, Bl Li et al., 9 88
St, Up
0.22 O, G St-A v 1 6 75 Chapter 25
0.30 O, G St-A v 3780 Chapter 25

4.0 0 St-A v 0-400 Roadifer, 1 9 87
0.8 2.6 0 D, A v 400-1 800 Paraschiv & Olteanu, 1 9 70

0 St-A Lt, V 700-4600 5-25 Chapter 35