A Review of Waterflood Performance in Garrington Cardium A and B Pools, Unit No. 2
Authors: Chakravorty S.K. , Brown P.R. , Endsin N. 
Published: December 2007

This paper presents the evaluation and prediction of ultimate oil recovery after a petrophysical study of Garrington Cardium A and B pools. Reservoir sands are discussed in detail and waterflood performance is emphasized. Surfactant treatment to improve oil production is described.

Introduction

The Garrington Upper Cretaceous Cardium field is located about 60 miles northwest of Calgary (Fig. 1) and has two pools, upper Cardium A and lower Cardium B sandstones, separated by about 100 ft of shale. Both sands trend northwest-southeast. Sand A trends for 36 miles with a producing width of about 6 miles. Sand B trends for 42 miles with a maximum width of 1 1/2 miles (Fig. 1). Thicknesses vary, but the maximum is about 20 ft in both pools.

The field was discovered in 1954 and waterflood operations began in 1965. This field has four units, but this study discusses only the geology and waterflood performance of Unit 2 (Fig. 1). Knowledge of the origin and performance of Unit 2 (Fig. 1). Knowledge of the origin and postdepositional history of these sands leads to a better postdepositional history of these sands leads to a better understanding of the waterflood performance.

Basic rock types were determined by examining detailed cores, measuring mercury-injected capillary pressure, and scanning electron microscope. Rocks were pressure, and scanning electron microscope. Rocks were classified as "good" or "poor" in terms of reservoir potential. Significant differences in the production and potential. Significant differences in the production and waterflood history of Sands A and B can be related to their geological characteristics.

Geology

Cardium A sand correlates with the producing sand of Pembina field 60 miles northwest. However, it is thinner Pembina field 60 miles northwest. However, it is thinner with poorly developed, clean sand beds. The most distinctive feature of Sand A is the extensive mottling caused by burrowing organisms that mixed sand, silt, and mud together. This action greatly reduced the effective porosity and, particularly, the permeability of the sand; porosity and, particularly, the permeability of the sand; but, more importantly, it destroyed much of the lateral continuity of the sand beds. Thinly laminated, well sorted, clean, fine-grained sandstones are seldom more than 1 to 2 in. thick.

Sandstones are composed mostly of quartz and lesser chert grains, with only minor amounts of feldspar, mica, and rare glauconite. X-ray diffraction analysis shows that the dominant clay minerals are illite, chlorite, and kaolinite, with traces of montmorillonite. The kaolinite is well crystallized and probably of diagenetic origin.

At the top of the Sand A sequence, there is usually a conglomerate bed that varies from 1 in. to nearly 3 ft thick. This is composed of well rounded chert, quartz, and argillite pebbles embedded in a dense shale matrix. Although nonporous, the conglomerate has well developed, vertical fractures. Laterally, Sand A grades into siltstones and silty shale. Textures and structures indicate that Sand A was deposited in a shoreface environment. Comparison of this conglomerate with that at Pembina and elsewhere indicates that the beds formed as bars on top of an offshore shoal, possibly as a terrace bar, as suggested by Swagor et al. for Cardium conglomerate at Carrot Creek.

Sand B is different both in distribution and mineralogy. Its most striking feature is the length of its body relative to width.

JPT

P. 869