Henry Tan

Integrated interpretation of borehole and crosswell data from a west Texas field

The accurate estimation of rock properties between wells is crucial to the problems of reservoir development and enhanced oil recovery. Recent advances in cross‐borehole seismic technology have allowed cross‐borehole tomography to be used as a high‐resolution tool in estimating P-wave velocities between boreholes. In this case history, we describe acquisition, processing, and preliminary interpretation of cross‐borehole data in a west Texas oil field. In addition to interwell velocity estimation, we show estimates of porosity between wells obtained through use of tomography and velocity‐porosity relationships.

Integrated reservoir characterization : beyond tomography

In 1992, there was a collaborative effort in reservoir geophysics involving Amoco, Conoco, Schlumberger, and Stanford University in an attempt to delineate variations in reservoir properties of the Grayburg unit in a West Texas CO2 pilot at North Cowden Field. Our objective was to go beyond traveltime tomography in characterizing reservoir heterogeneity and flow anisotropy. This effort involved a comprehensive set of measurements to do traveltime tomography, to image reflectors, to analyze channel waves for reservoir continuity, to study shear‐wave splitting for borehole stress‐pattern estimation, and to do seismic anisotropy analysis. All these studies were combined with 3-D surface seismic data and with sonic log interpretation. The results are to be validated in the future with cores and engineering data by history matching of primary, water, and CO2 injection performance. The implementation of these procedures should provide critical information on reservoir heterogeneities and preferential flow direc...

Crosswell seismic imaging: A technology whose time has come?

We start with a description by Marty Williams, an exploitation geophysicist with Amoco, of his experiences with with crosswell seismic.

Glenn Pool project: Crosswell seismic data acquisition overview

A two-day crosswell seismic field test survey was conducted in late August 1993. The test was successful in determining operational procedures and parameters for a (latter) full crosswell survey. This paper focuses on some of the deterministic field test results for the survey design. Various data acquisition parameters such as vertical stack, source spacing, sweep signal range are compared independently for improved data quality. The distance between the survey wells and data aperture controls the signal transmission range. Considering the pre-designed acquisition window and first arrival signal strength, a maximum interwell spacing is determined. A new well to be used in the full survey was spotted and drilled. The test survey was not intended for subsurface imaging. Ray coverage and ray density were insufficient for full velocity inversion. However, an initial attempt of processing the first arrival times resulted in an incomplete but promising tomographic reconstruction. Average velocities in the well-illuminated zone are in good agreement with sonic log data. The full crosswell survey was completed in early 1994. When processed, these will result in three P-wave tomograms two of which are oriented in the North-South direction and third extending approximately orthogonal to the other two.

Cross-borehole analysis of velocity and density

Abstract Cross-borehole tomography and borehole gravity meter (BHGM) surveys allow estimations of seismic velocity and rock density to be made in the vicinity of a borehole. Two such surveys recently conducted in Oklahoma and onshore Gulf Coast sediments show some of the first applications of these combined technologies. The results show an encouraging correlation between density and P-wave velocity for these borehole surveys in shallow clastic sediments. Such a correlation is predicted by Gardners equation.