The Long Beach Unit (East Wilmington Field, California) consists of nearly a thousand active wells and currently produces about 47,500 BOPD. Values of the in-situ stresses are needed for designing hydraulic fracture stimulation treatments. Estimation of the stresses is complicated by the fact that the field is in an active strike-slip tectonic regime where the vertical stress magnitude is intermediate between the minimum and maximum horizontal stresses. Stress magnitudes from casing-leakoff tests and density log calculations are consistent with this structural interpretation,

Stresses were directly measured in several casing-leakoff tests, micro-fracs, and mini-fracs performed in various sands and shales in the field. The minimum horizontal stress in the shales is roughly linear with depth, while in the sandstones it increases more rapidly, and is more variable than in the shales.

This paper presents a semi-empirical model for calculation of in-situ stresses from logs. It assumes that the stresses are determined by a mechanical stability criterion, and that the ratio of the mean horizontal effective stress to the vertical effective stress is constant from one formation to another. This ratio can be determined from casing-leakoff tests. The new model matches the observed stress contrasts better than conventional elastic models.

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