Showing papers on "Measured depth published in 1991"
TL;DR: In this paper, an inverse problem is formulated to estimate both the direction of the minimum horizontal stress and the relative magnitudes of the horizontal stresses to the vertical stress in vertical holes.
Abstract: Well bore breakouts are zones of spalling and fracture that form on opposite sides of a well bore and tend to change the cross-sectional shape of the borehole from circular to roughly elliptical. In vertical holes drilled in areas where one principal stress is vertical, breakout orientations tend to parallel the direction of the regional minimum principal stress (compressive). Such breakout orientations are often valuable indicators of the direction of the principal stresses. We will show in this paper that the variation of the breakout direction as the borehole deviates from vertical gives further information about the relative magnitudes of all the three principal stresses. Based upon the variation of breakout directions as a function of deviations and azimuths of the borehole along its depth, an inverse problem is formulated to estimate both the direction of the minimum horizontal stress and the relative magnitudes of the horizontal stresses to the vertical stress. Tests with synthetic data sets show that the power of the method is dependent on the stress regime (strike-slip, normal and thrust). Generally the inverse problem in the case of thrust faulting is less constrained, whereas, in the case of normal faulting, it allows for a determination of all three parameters (SH/SV, SK/SV and ν) with a reasonable certainty. Interpretation of the data from the Siljan Deep Drilling Project in Sweden shows that the azimuth of the minimum principal horizontal stress is very well constrained to N(18.4°±0.3°)E, while the ratio of the maximum principal horizontal stress to the vertical stress is constrained to 1.1 ±0.1. The ratio between minimum principal horizontal stress and principal vertical stress is poorly constrained to the interval (0.0–0.95). Information of drilling mud leakage and borehole stability analysis provides a value of 0.61 [Stephansson et al., 1990]. These results are in fair agreement with the results from earthquake fault plane solutions in South Central Fennoscandia with dominant strike-slip faulting and an inferred minimum horizontal stress direction of N45°E [Slunga, 1981].
30 citations
Patent•
27 Aug 1991
TL;DR: In this paper, a record subjected automatically to sound velocity correction on a recording paper was obtained by simultaneously holding the actual depth of water at every falling depth of a reflecting body at the time of checking of a bar and a measured water depth obtained by a water depth measuring circuit in a memory.
Abstract: PURPOSE:To obtain a record subjected automatically to sound velocity correction on a recording paper by simultaneously holding the actual depth of water at every falling depth of a reflecting body at the time of checking of a bar and a measured water depth obtained by a water depth measuring circuit in a memory. CONSTITUTION:The measured depth (n) at every falling depth of a reflecting body and the actual depth data (l) of the reflecting body from a reflecting body depth measuring circuit 29 are stored in a sound velocity correcting memory 32 as bar check data. The output signal (c) of an A/D converter 14 is inputted to a usual depth measurement data memory 15 and a water depth measuring circuit 31 and the output signal (m) from a writing clock pulse generating circuit 30 is inputted to a writing address signal generating circuit 17. An operation circuit 33 reads the bar check data (o) held in the sound velocity correcting memory 32 at the time of the checking of a bar and compares the depth measurement data (n') from the circuit 31 with the depth measurement data (n) in the data (o) fed through the circuit 31 to calculate a sound velocity correction value g' to input the same to the circuit 30. The circuit 30 outputs a writing clock pulse (m') subjected to sound velocity correction for the purpose of next time depth measurement.
3 citations
TL;DR: In this article, the authors examined the size of the borehole effect in this context and showed that the effect is on the order of 1 μgal, just below the sensitivity of traditional gravimeters.
Abstract: Borehole gravimetry measurements are affected by the presence of the borehole at the top and the bottom of the borehole. Less frequently recognized is a borehole effect in the vicinity of the formation bed boundaries across which density varies. The borehole effect is usually insignificant. In typical oil well conditions with 1-m station spacing, the borehole effect is on the order of 1 μgal, just below the sensitivity of the traditional gravimeters. However, the borehole effect can be significant when the station spacing is not much larger than the borehole radius and also in applications with small tolerance to error. For example, determination of oil saturation accurate to 10 percent requires on the order of 0.3 μgal/meter sensitivity. New gravimeter technologies (Prothero and Goodkind, 1968) and developments in gradiometers (Chan, Moody, and Paik, 1987) promise higher sensitivity and resolution, which call for more detailed environmental corrections. The purpose of this note is to examine the size of the borehole effect in this context.