Abstract

Predicted waterflood performance in the Dodsland Viking Field has not occurred. Previous study identified that the effects of hydraulic fractures must be taken into account in order to predict performance. The revised predictions are still somewhat optimistic when compared to actual production. The previous work has been extended to account for reservoir layering.

Core data has been used to provide a quantitative analysis. Due to extreme permeability contrasts, it is difficult to simulate large ranges information permeability as separate layers. Hearn type relative permeability curves were therefore used.

With high reservoir heterogeneity, waterflood response may consist only of a levelling of production. This prediction is consistent with actual well performance observed. The methodology used and its limitations are discussed. Additionally, the effects of well spacing and fracture extension are presented. This has important existing and work for economic implications planned waterfloods:

  1. Wells which are producing below their economic limit, awaiting predicted waterflood response, can be shut in. This was used to implement substantial reductions in operating costs.

  2. More realistic estimates of waterflood response in highly stratified reservoirs can be made, prior to implementation using core data.

Introduction
Outline

This paper follows the layout of a study originally made for an individual unit. The methodology and results are explained under the following headings:

  • The geology of the field is reviewed.

  • The production performance of the field is discussed.

  • The assumptions upon which the simulation model was based arc summarized.

  • The results of various type sensitivities are presented.

Conclusions are then made.

This work is an extension of work done previously by Carlson and Andrews1. Although this paper has been written on a stand alone basis, further background data may be found in the previous paper.

Background

The Dodsland field, located in south-west Saska tchewan, was first discovered in 1953. The location of the field is shown in Figure-l. Light oil (36 degree API) production is obtained from the Cretaceous aged Viking sandstone.

Delineation of the field occurred rapidly during the 1950's. Unitization and waterflooding followed in the mid 1960's. A resurgence in development occurred in the late 1970's and early 1980's due to high oil prices. Development in the mid 1980's was also fuelled by attractive government incentives.

Geological Description
Lithology

The Viking consists of an interbedded shale and sandstone. The sandstone is a poor reservoir rock; its shallow drilling depth and large area have permitted extensive development.

The lithology has been described in detail by Tooth et al 2. The sandstone portions typically consist of sublitharenates which locally grade into siltstones of similar composition. Porosity is intergranular with significant amounts of micro-porosity associated with clay mineral assemblages. Cementing by silica, siderite, pyrite and kaolinite is poor.

The more productive areas of the reservoir arc comprised of 15 to 25 foot thick sandstones with discrete shaly partings. In the less productive areas, the shale partings are dense and the pay consists of thin lenses of sandstone.

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