High‐resolution crosswell imaging of a west Texas carbonate reservoir: Part 1—Project summary and interpretation

Abstract

A carbon dioxide flood pilot is being conducted in a section of Chevron's McElroy field in Crane County, west Texas. Prior to CO 2 injection, two high-frequency crosswell seismic profiles were recorded to investigate the use of seismic profiling for high-resolution reservoir delineation and CO 2 monitoring. These preinjection profiles provide the baseline for timelapse monitoring. Profile #1 was recorded between an injector well and an offset observation well at a nominal well-to-well distance of 184 ft (56 m). Profile #2 was recorded between a producing well and the observation well at a nominal distance of 600 ft (183 m). The combination of traveltime tomography and stacked CDP reflection amplitudes demonstrates how highfrequency crosswell seismic data can be used to image both large and small scale heterogeneity between wells: Transmission traveltime tomography is used to image the large scale velocity variations; CDP reflection imaging is then used to image smaller scale impedance heterogeneities. The resolution capability of crosswell data is clearly illustrated by an image of the Grayburg-San Andres angular unconformity, seen in both the P-wave and S-wave velocity tomograms and the reflection images. In addition to the imaging study, cores from an observation well were analyzed to support interpretation of the crosswell images and assess the feasibility of monitoring changes in CO 2 saturation. The results of this integrated study demonstrate (1) the use of crosswell seismic profiling to produce a high-resolution reservoir delineation and (2) the possibility for successful monitoring of CO 2 in carbonate reservoirs. The crosswell data were acquired with a piezoelectric source and a multilevel hydrophone array. Both profiles, nearly 80 000 seismic traces, were recorded in approximately 80 hours using a new acquisition technique of shooting on-the-fly. This paper presents the overall project summary and interpretation of the results from the near-offset profile.

High Resolution Definition of Subsurface Heterogeneity for Understanding the Biodynamics of Natural Field Systems: Advancing the Ability for Scaling to Field Conditions

“…Mason, 1981 andPeterson, et al, 1985). More recently, crosswell S-waves have also been used to map S-wave velocity (Harris, et al, 1995) and both P-and S-wave crosswell reflectivity have been analyzed for structural delineation ( Rector, et al, 1995). Until our work in fractured rock nearly all crosswell seismic tomography has been performed in sedimentary formations important to oil and gas exploitation (Rector, 1995).…”

Integration of advanced geoscience and engineering techniques to quantify interwell heterogeneity in reservoir models. Final report, September 29, 1993--September 30, 1996

“…The thin sections were made from the same regions of the cores that were used for minipermeameter measurements. The objectives from petrographic analysis were (1) to relate variations in permeability to variations in rock composition or fabric, (2) to provide additional details for determination of depositional environments, and (3) to understand how variations in deposition and diagenetic history of the different rock types impacted reservoir quality.…”

“…In the Well No. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] core, this interval contains low angle cross-bedded red gray sandstones that are interpreted to be eolian sands, possibly deposited by dunes or sand sheets prograded across the coastal sabkha. Eolian origin for this sandstone is based on the high degree of grain rounding and sorting, the reddened clay coatings of many grains, and the low angle cross laminations.…”

“…This gave a preliminary velocity model for synthetic traveltime modeling. We then smoothed this velocity model with a moving triangular window consisting of 3 points with weights (1,2,1). The resulting velocity (slowness) model is shown in Fig.…”

Elastic properties of sand-peat moss mixtures from ultrasonic measurements

“…Other parameters such as porosity, permeability, and fluid saturation are important to site characterization. Electrical methods have been used to quantify these parameters, and studies (Harris et al, 1995 suggest that these methods could be combined with seismic information about compressional and shear velocities to image the shallow subsurface. l Motivation Lawrence Livermore National Laboratory has been involved in the effort to find a cost-effective alternative to current methods of contaminated site characterization.…”