Abstract

The Bigoray Cardium “B” Pool is located in Twps. 50 and 51, Rge. 9 W5M in West Central Alberta. It is 10 to 15 miles north of the Pembina Cardium Field and approximately two miles north of the Cynthia-Pembina Field. (See Sections A, B, and C).

A detailed geological and petrophysical study of this Cardium conglomerate oil pool was undertaken with the objectives of explaining poor secondary recovery, and providing reservoir parameters/layering model for a simulated reservoir model. As a result of these studies, it was concluded that many Cardium lithofacies types, each with their own inherent reservoir characteristics, were complexly assimilated to form this reservoir. The distribution of these lithofacies types, in conjunction with siderite barriers bisecting this pool, cause a restricted lateral waterflood sweep. Augmenting these observations is the unfavourable injector/take-point pattern.

Reservoir architecture was quantified by summing the seven lithofacies identified, into five lithofacies assemblages (see Sections D and E). The distribution of these lithofacies assemblages was influenced by sediment source direction, location and times of conglomerate deposition, longshore drift, and wave and storm generated energy. The best reservoir parameters occur along the axial portion of the pool, where the clast supported conglomerate is the thickest.

Petrophysical examination of the lithofacies assemblages resulted in the definition of unique porosity/permeability, and core porosity/bulk density log porosity algorithms for each assemblage (see Section F). Correlation coefficients were greatest for those lithofacies assemblages dominated by lithofacies with unimodel grain size distribution. A curvilinear porosity/permeability algorithm (on a semilog plot) best defines the most conglomeratic facies assemblages, whereas a linear porosity/permeability algorithm best defines the others. An overall trend of decreasing average permeability and increasing average porosity was recognized as one goes from facies assemblages dominated by clast support conglomerate, through sandy conglomerate, to sandstone and shaly conglomerate.

Shales were deposited within the conglomerate interval during periods of quiescence between high energy, conglomerate dumping events (see Section E). The variation in clastic deposition was partially the result of sea level fluctuation. These shales were penecontemporaneously sideritized as confirmed by fresh water, meteoric oxygen isotope signatures (R. Walker, Pers. Comm.). The siderite bands occur as clinoformal units between en echelon conglomerate “shingles”. They act as barriers to fluid flow in the vertical and lateral directions, and they promote flow along the length of the Bigoray Cardium “B” pool, parallel to depositional strike (see Section G).

In summary, reservoir heterogeneity within the Bigoray Cardium “B” oil pool is resultant from diagenetic and depositional heterogeneity, both of which affect the production behavior/fluid flow.