Changes

===Step 5. Continuity analysis===

===Step 5. Continuity analysis===

The objective of this step is to prepare a model that describes the three-dimensional distribution of the major diagenetic components represented on the vertical well profiles. The accuracy of and confidence in these correlations are governed by such factors as (1) the uniqueness of the profiles constructed, (2) the degree of heterogeneity within the reservoir (see “[[Geological heterogeneities]]”), (3) the degree to which the sample coverage in each well represents the variations present within the reservoir, (4) how well the geologist understands the origins of and factors controlling the distribution of the major diagenetic alterations, (5) the well spacing, and (6) the thicknesses of the diagenetic zones.

The objective of this step is to prepare a model that describes the three-dimensional distribution of the major diagenetic components represented on the vertical well profiles. The accuracy of and confidence in these correlations are governed by such factors as (1) the uniqueness of the profiles constructed, (2) the degree of heterogeneity within the reservoir (see [[Geological heterogeneities]]), (3) the degree to which the sample coverage in each well represents the variations present within the reservoir, (4) how well the geologist understands the origins of and factors controlling the distribution of the major diagenetic alterations, (5) the well spacing, and (6) the thicknesses of the diagenetic zones.

Although some diagenetic components may display abundance trends that follow or are only slightly discordant with depositional trends, others may occur at large angles to the latter. Some of the more common distributions of diagenetic components and the geological factors controlling these distributions are listed in Table 3.

Although some diagenetic components may display abundance trends that follow or are only slightly discordant with depositional trends, others may occur at large angles to the latter. Some of the more common distributions of diagenetic components and the geological factors controlling these distributions are listed in Table 3.

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The basic correlation techniques in common use include marker and sequence analysis and, where continuity is very limited, slice techniques<ref name=pt06r18>Cant, D. J., 1984, Subsurface facies analysis, in Walker, R. G., ed., Facies Models: Geoscience Canada, Reprint Series 1, p. 297–319.</ref>. Correlation of diagenetic zones is most accurate when the origins and timings of the diagenetic events creating the components of interest are well understood, the sample and well spacing are relatively small, the diagenetic zones are relatively thick, and the sequence of zones is unique.

The basic correlation techniques in common use include marker and sequence analysis and, where continuity is very limited, slice techniques.<ref name=pt06r18>Cant, D. J., 1984, Subsurface facies analysis, in Walker, R. G., ed., Facies Models: Geoscience Canada, Reprint Series 1, p. 297–319.</ref> Correlation of diagenetic zones is most accurate when the origins and timings of the diagenetic events creating the components of interest are well understood, the sample and well spacing are relatively small, the diagenetic zones are relatively thick, and the sequence of zones is unique.

The distribution of reservoir fluids or pressures at the time of discovery of the reservoir, or at subsequent intervals during field development, may indicate the presence of continuous permeability barriers and thus may help to confirm the extent of some diagenetic zones. When the basic correlation techniques prove unsatisfactory or inadequate due to a high degree of complexity or low degree of confidence, the geologist may need to resort to special engineering techniques such as pulse testing (Pierce, 1977) or tracer studies (Wagner, 1977) (Table 4), or to probabilistic modeling (Hewett and Behrens, 1988) (see Part 8).

The distribution of reservoir fluids or pressures at the time of discovery of the reservoir, or at subsequent intervals during field development, may indicate the presence of continuous permeability barriers and thus may help to confirm the extent of some diagenetic zones. When the basic correlation techniques prove unsatisfactory or inadequate due to a high degree of complexity or low degree of confidence, the geologist may need to resort to special engineering techniques such as pulse testing (Pierce, 1977) or tracer studies (Wagner, 1977) (Table 4), or to probabilistic modeling (Hewett and Behrens, 1988) (see Part 8).