It is useful to map hydraulic fractures in order to improve the rate of success of such operations and to optimize the pattern of stimulated wells. The proposed method can be used during a minifracturing or prefracturing operation and necessitates a downhole 3D acoustic detector clamped in the well. A few to a few dozen cubic meters of gel are injected during fracturing phases, and the acoustic activity is recorded after every injection. Then signals containing apparent P and S waves are analyzed to determine the directions and distances of the emitting sources. A number of arrivals cannot be interpreted easily, in particular those corresponding to refractions along the casing.Three field examples corresponding to a vertical, a deviated and a slant well are given. Knowing the P and S wave velocities in the different layers and a careful choice of the tool position are essential to the success of the method.

TX 75063-3638, U.S.A., fax 01-972-952-9435. AbstractMechanical and kinematics data at the bit have been collected during drilling operations and organized to identify optimal drilling efficiency. Transitional conditions towards abnormal behavior have been distinguished. Normal drilling is usually characterized by regular linear relationships between global control variables at the bit, which approximately correspond to an up scaling of a local Mohr Coulomb type failure mechanism of the rock. Most of our experimental data confirm this classical disposition. However, considerable departure from these relationships is noted, especially when there is BHA resonance or when there is partial balling at the bit. The field tests presented here allows us to verify classical theory and to draw up new guidelines for behavior in nonoptimal or dangerous, evolving operating conditions, such as those that occur under poor cleaning conditions. The main features of a mechanical structuring model involving transition towards low efficiency conditions are presented, and it is shown how this model confirms our interpretation of field data. The model couples the drillability of rock and the general dynamics of the bit in an original and synthetic way. It makes it possible to understand and test the sensitivity of bit response to variables such as "weight on hook", torque on the drillstring and flow rate of the fluid.

The vertical distribution of the minimum horizontal in-situ stress is . the major parameter which controls the confinement height and direction of hydraulic fractures. The ininifrac technique has been extensively used to collect these data. However, its implementation in the payzone and adjacent layers is often hindered by technical and economic considerations. Consequently, the determination of the stress field on the basis of laboratory measurements in orientated core samples has been investigated. New developments and the results of three methods are described: anelastic strain recovery (ASR), differential strain curve analysis (DSCA), core discking analysis. The results obtained using these methods on cores extracted from several wells are described and discussed. A comparison is made with data available from minifracs, logs and regional tectonics. The main conclusions are that different methods give a good idea of the principal horizontal stress.

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