Biddle and wielchousk Lateral depositional Buried depositional changes toe-of-slope marls and sh carbonates porous reef and Facies change Eolian dune Depositional pinchout Submarine fan lobe Hydrocarbon accumulation itional stratigraphic traps. (A) Traps created by lateral changes in sedimentary rock type during p: juxtaposition of reservoir and seal caused by lateral facies changes. Bottom: reservoir termination due to al pinchout of porous and permeable rock units. B)Traps formed by buried depositional relief. In each entary processes form a potential trapping geometry, but require burial by younger impermeable section to sIred top sea tion structural-stratigraphic traps, particularly if the between the forereef rocks and adjacent basinal deposits structure was growing during deposition of the reservoir (potential source rocks) can create excellent migration and seal rocks pathways. Formation of a top seal requires that reef The second general class of primary stratigraphic growth is terminated and that the reef is buried beneath traps is associated with burea p ejeogeomorphic type of trap is accurate prediction of porosity and perme- a cap of low-permeability material. a key risk for this traps are equivalent to the constructive pa such traps, a few of which are illustrated in Figure 137B. of the Western Canada sedimentary basin are excellent Each of these has distinct characteristics and attendant examples of this type of trap (Hemphill et al. 1970; Barss Carbonate reefs provide a classic example of potential Another type of buried depositional relief is associ- raps associated with buried depositional relief. Reef ated with some submarine fan deposits (Figure 13 7B).In growth with time enhances depositional relief, and the such depositional settings, sand-rich depositional lobes transition from tight lagoonal rocks to porous and may be encased in shale. The Balder oil field in the permeable backreef-reef-forereef rocks may provide a Norwegian section of the North Sea is an example of this good reservoir-lateral seal combination. The relationship type of trap(Sarg and Skjold, 1982)228 Biddle and Wielchowsky A Lateral depositional changes Facies change Depositional pinchout B Buried depositional relief *9&J2* 1 1 " 1 " f ^*V l ' i i i tight ^v i . i i carbonates ">*U . 1 ' y^*^i^_\ porous reef and forereef carbonates toe-of-slope and basin carbonates, ^. marls and shales I A*s. i ^V^ \ ^ i M X-T"1 ^^™™ Reef Eolian dune Submarine fan lobe ||f| Hydrocarbon accumulation Figure 13.7. Primary or depositional stratigraphic traps. (A) Traps created by lateral changes in sedimentary rock type during deposition. Top: juxtaposition of reservoir and seal caused by lateral facies changes. Bottom: reservoir termination due to the depositional pinchout of porous and permeable rock units. (B) Traps formed by buried depositional relief. In each example, sedimentary processes form a potential trapping geometry, but require burial by younger impermeable section to create the required top seal. tion structural-stratigraphic traps, particularly if the structure was growing during deposition of the reservoir and seal rocks. The second general class of primary stratigraphic traps is associated with buried depositional relief. These traps are equivalent to the constructive paleogeomorphic traps of Martin (1966). There are many different types of such traps, a few of which are illustrated in Figure 13.7B. Each of these has distinct characteristics and attendant trap risks. Carbonate reefs provide a classic example of potential traps associated with buried depositional relief. Reef growth with time enhances depositional relief, and the transition from tight lagoonal rocks to porous and permeable backreef-reef-forereef rocks may provide a good reservoir-lateral seal combination. The relationship between the forereef rocks and adjacent basinal deposits (potential source rocks) can create excellent migration pathways. Formation of a top seal requires that reef growth is terminated and that the reef is buried beneath a cap of low-permeability material. A key risk for this type of trap is accurate prediction of porosity and perme￾ability within the reef complex. The Devonian reef fields of the Western Canada sedimentary basin are excellent examples of this type of trap (Hemphill et al., 1970; Barss etal,1970). Another type of buried depositional relief is associ￾ated with some submarine fan deposits (Figure 13.7B). In such depositional settings, sand-rich depositional lobes may be encased in shale. The Balder oil field in the Norwegian section of the North Sea is an example of this type of trap (Sarg and Skjold, 1982)