Abstract

Over the lifetime of a well it is possible that several squeeze operations will be performed depending on scaling severity. Downhole squeeze operations have been performed for many years and have on the whole been an effective scale management tool. However, the long term impact that successive squeezing has on treatment lifetime and well productivity has received little attention. This paper will address these issues by comparing the results from a unique sequence of long term corefloods that were designed to replicate five successive treatments on the kaolinite rich, Middle Tarbert core from the StatoilHydro operated field, Oseberg Sør. Relatively few squeeze treatments have been performed on this field, and the coreflood results have been up-scaled to provide a potential prediction of the effects of long term squeezing and well productivity on Oseberg Sør. Furthermore, the laboratory results have been cross-checked by comparing with the Heidrun field that has been squeezed for many years. Heidrun is an analog of Oseberg Sør with kaolinite rich producing intervals and similar productivity issues related to kaolinite mobilisation.

Introduction

In many respects the opening sentence of Vetter's article (Vetter, 1973), "There are a number of gaps in our knowledge of the principles involved in the squeezing process," is still valid 25 years after publication. This paper will address one of those identified knowledge gaps which is the effect that well lifetime squeezing has on treatment performance and productivity. Depending on the scaling severity, a well can require squeeze treatment as often as 10 days as is the case for the Miller field (Wylde et al, 2007) or after several months, e.g. Oseberg Sør field (Fleming et al, June 2007). With regards to the latter field, a study was initiated to determine the long term impact of squeeze treatment on well performance and this forms the basis for the paper. The laboratory results will also be compared to the StatoilHydro operated Heidrun field that has been squeezed over several years.

The Oseberg Sør field is situated 130 km west of the Norwegian coast on the eastern flank of the Viking Graben structure (Fig. 1). It consists of fault bounded structural units of varying geological complexity. Within these units the reservoir intervals are of moderate to poor quality and can exhibit strong contrasts in permeability and formation water composition. Reservoir pressure support is provided by combined injection of gas and Utsira aquifer/produced water. The wells are a combination of platform and subsea and include extended reach horizontals with complex geometry and lesser numbers of vertical wells.

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