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Abstract

This paper reviews the field experience with the use of foam for improved recovery from oil reservoirs and attempts to transfer this experience to foam processes as they might be applied in North Sea reservoirs. The review of published field trials, mainly from North America, is augmented by a simulation study on a generic North Sea reservoir, covering the foam process options of greatest relevance and their sensitivity to selected reservoir, foam, and process parameters. 30 field projects have been critically evaluated with the main objective of assessing the potential of foam in a North Sea environment. For this purpose, foam processes are categorized by the desired mechanisms of action of foam: in-depth mobility control, diversion, or GOR control in production wells. A set of target foam properties (an "ideal foam") is defined for each category. Despite the differences in conditions, the field trials allow extracting significant information relevant for the comparison. It is concluded that foam has significant potential in North Sea reservoirs. The degree of recovery improvement varies between the process options and with the degree of vertical communication between reservoir layers or units. Of the foam parameters considered, the sensitivity to mobility reduction factors is the strongest with high MRF being most favorable.

Introduction

The high mobility of gas in a reservoir may cause a number of flow problems, summarized in Figure 1. A foam confined inside the pore network has many properties that are desirable for controlling gas flow. The dispersed microstructure of pore-bridging liquid films separating individual gas bubbles gives foam its unique ability to selectively reduce gas mobility. Foam has the potential of alleviating all the problems illustrated in Figure 1. Foam has been used or considered for increasing the sweep efficiency of injected gas (vertical and aerial), for blocking and diverting injected gas from entering high-permeable zones or fractures, and in treating production wells suffering from unacceptably high gas/oil ratio (GOR) levels.

Several foam pilot tests are presently being considered for North Sea oil reservoirs. Foam is a priority topic in the on-going Norwegian IOR research program RUTH, and is studied in a dedicated subprogram. A recent RUTH-Foam report which is part of the basis for the present paper discusses potential uses of foam in the North Sea, based on a critical review of the existing field experience, mostly from open sources. A difference from other, more comprehensive (data bases such as that maintained by the U.S. DOE, is that our work contains judgements by the operators and authors in addition to "hard" data.

Foam process concepts

Three gaseous fluids are involved in foam processes; steam, CO2, various hydrocarbon gases (HC) and N2.

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