Abstract

There is an ever increasing need to quantify the in situ properties of barriers and pay Zones in order to assess the potential for fracture containmentand to optimize stimulation treatment design. A major testing program has been conducted jointly by Dome Petroleum ltd., Dowell and Schlumberger to compare laboratory-measured mechanical properties with those determined by well logging.

The testing program was conf1ned to the Basal Quartz Formation at a depth of approximately 3,000 m, as it occurs in a Dome Well in the Caroline area of Alberta. Laboratory testing included the determination of Young's modulus and Poisson's ratio at in situ temperature and stress conditions.

The NPL was derived from the open-hole sonic log and the in situ stresses were measured in the field. An attempt has been made to explain the discrepancies on the basis of other known well data.

Introduction

Definition of mechanical properties of reservoir rocks is of major importance for simulation of reservoir performance and for designing hydraulic fracturing treatments. Ideally, identification of mechanical properties should be possible bywell logging techniques. To date, halo/ever, adequate correlation between logging predictions and material properties, measured in the laboratory under simulated reservoir conditions (temperature and pressure), is not always achieved. This paper is directed toward determining where d1screpancies exist and outlining procedures for modifying logging measurement interpretation. The ultimate goal is to have an adequate body of local information, based on controlled laboratory measurements and field experience, 1n order to allow for ready use of logging predictions, voiding the necessity of perform1ng expensive and time-consuming laboratory testing on every well.

Extensive laboratory measurements outlined subsequently in this paper are compared to predictions from Schlumberger's Mechanical Properties Log (MPl). This log presents predictions of lithology, shear modulus, Poisson's ratio, bulk modulus and fracture gradient.

According to Coates and Dena a (l980). "Lab studies show a d1stinct tie between lithology type and the shear/compressional velocity. Adapting this to log data, it is possible by ut111zing advanced synergetic methods of data processing todetermine the lithology type. Which with compressional velocity can be used to determine the shear velocity.

"To reproduce laboratory results with in situ measurements, 1t is necessary to consider the influence of clay volume, distribution and type, hydrocarbon type and saturation, the degree ofmud filtrate invas10n, and the fracture location and orientation within the rock matrix. Advanced interpretation principles using computer analysis are used to strip the compressional travel time of its hydrocarbon and borehole effects and separate it into matrix and clay responses. This information, with the exact lithology type and the laminated clay model, is then used to obtain a shear/compressional velocity and subsequently the des1red shear travel time."

Knowing the compressional and shear wave velocities, the following formulas are invoked.

Mathematical formulas (Available in full paper)

The weak link of the procedure may be the required intermediate "synthetic" log relating the compressional wave velocity to the shear wave velocity. logging measurement of the shear wavevelocity is currently a difficult and uncertain procedure.

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