Abstract

The Hibernia Field, located in about 80 metres of water, 315 km ESE of St. John's, Nfld., was discovered i" 1979. Of the 10 wells drilled, seven wells tested a 150 to 290 metre thick section of rock interpreted to have been deposited in a fluvio-deltaic environment. Located between depths of 3450 and 3890 metres subsea, the Early Cretaceous-age Hibernia Formation contains an estimated 1.4 BBbls of STOOIP.

Petrophysical properties obtained from wireline logs and core were evaluated using mathematical and statistical techniques to create alternative permeability profiles and to characterize the Hibernia Formation into "Hydraulic Units". A hydraulic unit is defined as a volume of the total reservoir rock within which geological and petrophysical properties that affect fluid flow (e.g. pore tortuosity, surface area per unit grain volume, and shape factor) are internally consistent and predictably different from those properties of other rock volumes. A derivation of the Kozeny-Cannan equation which utilizes overburden core-derived porosity and permeability, was used to construct "Flow Zone Indicator" (FZI) curves. The resulting curves were related to other log attributes using a quantitative probabilistic model to predict hydraulic flow units (and permeability) in wells that had poor or no care recovery.

Groupings of flow zones, derived by histogram analysis, were found to be generally coincident with intervals of rock types derived from lithological and paleoecological interpretation. Involving more than just magnitudes of permeability, hydraulic zones provide a fundamental unit for subsequent reservoir characterization and simulation. Discrimination of flow zones will also prove to be helpful in defining future well completion and workover practices.

Introduction

The Hibernia Field is an offshore oil development located in 80 metres of water, 315 Ion ESE of St John's, Newfoundland. Following its discovery in 1979, nine appraisal wells were drilled from 1980 to 1984. Construction of the Gravity Base Structure (GBS) production platform started in 1990, with initial production scheduled to start in 1997. The Hibernia structure is a complexly faulted, rollover anticline created or influenced by extensional faulting and salt diapirism. The primary reservoir, contained within the Early Cretaceous Hibernia Formation, occurs at an average drill depth of 3700 metres. Of the seven wells which tested the reservoir, five were cored. Sedimentological interpretation of 386 metres of recovered conventional core indicates the Hibernia Formation to be a preserved fluvially-dominated deltaic complex. Quantitative core analysis of 143 metres resulted in reservoir property ranges of 14.5 to 18 percent for porosity, 150 to 2000mD for permeability, and an average water saturation of 13 percent. An integrated geophysical and geological study resulted in the mapping of a reference case distribution of an oil in place resource estimated to be 1.4 billion barrels.

As part of a reservoir characterization process, HMDC and CORE Lab investigated the petrophysical attributes of the Hibernia Formation with regard to identifying flow zones. The results of the study provided an alternative assessment of the wells, complementing traditional log analyses that had been done previously. The objectives of the study were twofold:

  1. To identify flow zone indicators (FZI) that would characterize the cored intervals in the Hibernia reservoir.

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