Single Well Tracer Testing For Connate Water Saturation At Utikuma Lake: Field Application
Authors: Hamp T. , Stokes D. , Wasylycia N. , Mayder A. , Odiorne J. 
Published: March 2010

Three Single Well Tracer (SWT) tests for Connate Water Saturation (Swc) have been successfully conducted in the Keg River Sand at the major Utikuma Lake oilfield, leading to significant reductions in estimated Swc and increases in reserves.

Resistivity logs and conventional core analysis yield erroneously high Swc in the Utikuma Keg River Sand due to thinly interbedded sands and shales, and severe wettability alteration in restored core. SWT testing allows in situ measurement of Swc in productive sand intervals only, investigating saturations within a 5 m radius of investigation.

The Utikuma tests represent the latest 3 of 10 tests conducted worldwide. They are the first SWT tests for Swc to use a novel downhole equipment configuration to avoid plugging by waxy crude. They also introduced the use of ethyl formate as the primary tracer for accurate measurement of Swc in 5% to 15% range. SWT results are supported by NGT/GST logs run during the programs, and the first public verification by oil base Core.

Introduction

Utikuma Lake Field is located north of the town of Slave Lake, Alberta, between the Nipisi and Red Earth fields (Fig. 1). Field characteristics are summarized in Table 1.

Utikuma produces 1500 m3/d of light, sweet oil under primary water drive from 180 wells completed in the Keg River Sandstone. The Keg River sands are deposited in Utikuma as numerous separate pools, laid over geological unconformities in the Precambrian granite. Average porosities and permeabilities for the Keg River sands are 20% and 1000 mD. Average net pay is 3 m.

Utikuma Keg River oil is paraffinic with low asphaltene content. Oil properties are listed in Table 2. Formation water is highly saline, with 275 000 mg/l total dissolved solids, as indicated in the water analysis data presented in Table 3.

Connate Water Saturation Determination at Utikuma

Connate Water Saturations (Swc's) of 29% based on early log and special core data have been recognized for Utikuma Keg River pools since discovery. Recognized inaccuracies in open hole log data and concerns over reliability of early core flood data led to further investigation of Swc.

Accurate Swc data was required to calculate reserves and determine a development strategy for the field. Increased reserves and production gains by increasing reserves-based Maximum Rate Limitation (MRL) provided economic incentive to aggressively pursue the program of Swc determination through Single Well Tracer (SWT) testing described in this paper.

Swc from Resistivity Logs

Swc determination from conventional resistivity logs is hampered in the Utikuma Keg River Sandstone by thin interbedding of sands and shales, and bed thicknesses less than the 2.4 m vertical resolution of resistivity tools. Radioactive feldspars affect Gamma Ray response, preventing shaly sand analysis. Swc's of 30% to 60% are typically obtained from conventional and shaly sand log analysis in the Utikuma Keg River Sandstone.

Swc from Core

Utikuma Keg River sand is a feldspar-rich quartzose as indicated in the X-ray Diffraction analysis presented in Table 4.