Evaluation And Control Of The Nipisi Gilwood Unit No. 1 Waterflood
Authors: Edgson J. , Lederhouse T. 
Published: March 2010

This paper discusses theoretical concepts and field performance data which demonstrate the applicability of Pulsed Neutron – Production Log evaluation in monitoring waterflood performance. Although this paper is specific to the Nipisi Gilwood A Reservoir, the application is qualitatively relevant for similar reservoirs and Walerflood projects.

A sandstone reservoir of varying permeability with shale interbeds is difficult to waterflood uniformly. In an operation where varying permeability is not taken into account, those areas at high permeability will be swept first, resulting in premature water breakthrough. In this manner, much of the oil-in-place in unswept low-permeability regions may remain unrecovered due to the high cost associated with the production of wells where break- through has occurred. A combination of Production Logs and TDT* – K Logs can provide indications at the well bore of the uniformity or non-uniformity of the sweep. By adjusting injection and production profiles accordingly, sweep uniformity can be improved, resulting in increasedultimate waterflood recovery,

Introduction

Nipisi Gilwood Unit No.1 is located approximately 200 miles north-northwest of Edmonton (Fig. 1). It produces from a series of deltaic Gilwood sands in the Watt Mountain Formation of Middle Devonian age. Nipisi has been under waterflood enhanced recovery since March of 1969, and at present has 26 water injection wells and 176 oil production wells.

Associated with any waterflood project is water breakthrough. An evaluation of reservoir behaviour was initiated in the spring of 1975 to monitor waterflood patterns and sweep efficiency. Injection profiles were combined with Production-Log profiles and Pulsed Neutron – water saturation evaluations in an attempt to define oil and water distribution throughout the sand beds. During 1975 and 1976, profiles were obtained on 13 water injection wells and 11 production wells.

Reservoir Description

The Nipisi Gilwood A Pool is a stratigraphic reservoir consisting of sandstone of the Gilwood Member of the Watt Mountain Formation, with shale interbeds. The Gilwood overlies the anhydrites and dolomites of the Muskeg Formation, and is in turn overlain by the anhydrites and shales of the Fort Vermilion Formation (Fig. 2). The sandstone is arkosic to feldspathic, and as a result can appear relatively radioactive on the Gamma- Ray Log (Fig. 3). The sand varies in grain size from silt to pebbles. The reservoir pinches out in an updip direction along the eastern boundary of the unit(1).

The shale, when consistent, isolates the sand interbeds into discrete zones. Core analyses have shown that porosity, permeability and pay thickness vary greatly from one zone to another. The contrast of permeabilities in the sand layers makes it difficult to waterflood the reservoir uniformly. Layers of high permeability will be swept first, resulting in premature water breakthrough, and much of the oil-in-place in unswept low permeability layers may remain unrecovered.

In 1973, flood tests were done on native-state core samples from Well 250(2). The tests indicated average connate water to be 31 per cent and provided a water-oil relative permeability curve (Fig. 4).