Page 100 - Fundamentals of Gas Shale Reservoirs

80 SEQUENCE STRATIGRAPHY OF UNCONVENTIONAL RESOURCE SHALES

the New Albany into four third‐order sequences. Two of Montney formation
these sequences consist of TST and HST deposits and the Gamma ray (API)
other two also contain LST deposits, suggesting a somewhat
more basinal extent of the latter two. The same gamma ray HST
log patterns as observed in the previously mentioned shales
occur for this shale. Also, Bohacs and Lazar (2010) have MFS
demonstrated an overall second‐order downlap pattern onto
the basal TST (Fig. 4.11).

4.7 mESOZOIC rESOurCE SHaLE EXamPLES TST

4.7.1 montney Formation (Early Triassic)

The gas‐producing Montney Formation was deposited in the Third order sequence
western Canada sedimentary basin during marine transgres­
sion as shoreface, shelf, and slope deposits (Adams, 2009). It
sits unconformably (SB/TSE) upon the Permo‐Carboniferous (Channel
Belloy/Debolt formations (Fig. 4.12). LST sands)
The Montney is divided into two major third‐order
depositional sequences separated by a sequence boundary SB/TSE
that correlates to an Early Triassic global eustatic sea‐level
fall (Moslow and Davies, 1997). The lower Montney
consists of dark gray dolomitic siltstone interbedded with
shales; it comprises a third‐order TST and HST, which are TST/HST
further subdivided into a series of fourth‐ or perhaps fifth‐ Third order sequence 50 ft
order progradational parasequences (Moslow and Davies,
1997). The upper Montney consists of siltstone with inter­
laminated fine‐grained sandstones; it consists of, from SB/TSE
the base toward the top, third‐order LST turbidites (which
form reservoirs in part of the basin) and a TST/HST, Belloy/Debolt formations
which also is divided into a number of progradational
parasequences. FIGurE 4.12 Gamma ray log and sequence stratigraphy of the
Montney Formation. After Moslow and Davies (1997). The Montney
consists of two third‐order sequences (long, solid arrows) with
4.7.2 Haynesville/Bossier Shales (Late Jurassic) several superimposed higher frequency sequences (short dashed
arrows). Lowstand systems tract sandstones are present at the base
The Haynesville/Bossier shales were deposited over a 15 Myr of the uppermost third‐order sequence. Reprinted with permission
(140–155 Myr) time span in the US East Texas and North of Bulletin of Canadian Petroleum Geology, whose permission is
Louisiana salt basins during opening of the Gulf of Mexico required for further use.
(Hammes et al., 2011). The Haynesville comprises a third‐
order TST unconformably (SB/TSE) deposited during the
interval 155–151 Myr, overlying the Smackover/Haynesville 4.7.3 Eagle Ford Formation (Cretaceous)
Limestone (Fig. 4.13) (Goldhammer, 1998). The most widely recognized Mesozoic shale in the United
The overlying Bossier Shale is also interpreted as a third‐ States is the Eagle Ford Formation of Texas. It has been
order sequence separated from the Haynesville by a 151 Myr the main exploration and development target for many oil
regional unconformity (Fig. 4.13). Studies by Goldhammer and gas companies. Due to all the drilling over the past
(1998) and Hammes et al. (2011) have revealed a number of few years, the stratigraphy of the Eagle Ford has become
high‐frequency sequences superimposed upon the second‐ well established (Donovan and Staerker, 2010). A superb,
order sequence, each comprising a lower, organic‐rich TST complete outcrop of the entire Eagle Ford occurs at Lozier
and an upper calcareous mudstone HST (including low API Canyon (Fig. 4.14).
gamma ray/high‐density diagenetic dolomite marker beds) Based on surface and subsurface studies, a second‐order
(Fig. 4.13). The basal second‐order Haynesville TST is more sequence stratigraphic framework has been established
organic rich (up to 7 wt.%) than the Bossier, making it a which consists of a basal, high gamma ray TST/CS overlying
more prolific oil and gas producer. a clearly observable erosional surface (termed “K63SB”