In-situ residual oil saturation to gas from time-laps borehole gravity
- SPE, Richardson, TX (United States)
Three time-lapse borehole gravity surveys were performed one year apart in the dedicated data gathering and monitoring well of the Rabi oil-rim. For the first time, time-lapse density loss derived from Borehole Gravity Meter (BHGM) runs are used to estimate residual oil saturation in-situ. This is also the first time that the BHGM is used to determine interval density at one meter spacing. This paper reviews the planning of the BHGM surveys, explains why it became necessary to reduce the survey intervals to one meter, highlights the enhancements that made such measurements possible, and presents the first residual oil saturation results. BHGM density is derived from the gravity gradient measured between two survey depths. The accuracy of the BHGM density is therefore governed by the accuracy of both gravity and depth measurements. The uncertainty of the gravity difference between two survey depths was significantly reduced through sensor improvements and new processing techniques. Depth-related errors were practically eliminated using a {open_quotes}Shuttle Sonde{close_quotes} to accurately position the gravity sensor within intervals up to 2.5 m. The reproducibility of BHGM density measurements between different runs is {+-}0.015 g/cm{sup 3} (one-{sigma}, i.e. one standard deviation confidence level) over one meter intervals. This level of accuracy had only been achieved over three meter intervals prior to the present survey, thereby suggesting a threefold increase in the vertical resolution of the BHGM density measurement. As a result, a first estimate of residual oil saturation to gas was determined from BHGM data after only two years to within {+-} 10 su (one-{sigma}) on a one-meter survey interval.
- OSTI ID:
- 207313
- Report Number(s):
- CONF-951002-; TRN: 96:000704-0072
- Resource Relation:
- Conference: Annual meeting of the Society of Petroleum Engineers (SPE), Dallas, TX (United States), 22-25 Oct 1995; Other Information: PBD: 1995; Related Information: Is Part Of Formation evaluation and reservoir geology. 1995 SPE annual technical conference and exhibition; PB: 1010 p.
- Country of Publication:
- United States
- Language:
- English
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