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# HF-HR VSP results in geothermal GGR5 well

Charles Naville, James Bailey, Mary Humphries, Joséphine Vicelli, Frank

Hanot, Sebastien Soulas

► To cite this version:

Charles Naville, James Bailey, Mary Humphries, Joséphine Vicelli, Frank Hanot, et al. HF-HR VSP results in geothermal GGR5 well. Seminar on Geothermal Energy, SPWLA-France; Schlumberger, Jun 2024, CLAMART, France. 10.2516/stet/2024051. hal-04738185

HAL Id: hal-04738185

https://hal.science/hal-04738185v1

Submitted on 17 Oct 2024

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# HF-HR VSP results in geothermal GGR5 well

Charles Naville\*(IFPEN), James Bailey (VSPROWESS), Mary Humphries (VSPROWESS), Joséphine Vicelli (CDPconsulting), Frank Hanot (CDPconsulting), Sebastien Soulas (ASL).

## Abstract.

Defining 5m thin, or even thinner, porous reservoir beds was the feasibility objective assigned to the High Frequency/High Resolution (HF/HR) look ahead VSP survey to be recorded in the deviated section of a geothermal production well drilled down to the top of the carbonate Dogger aquifer in the Paris basin, around 1500m in vertical depth, with a landing angle of 65°. The idea was to predict the depth of the first porous bed to be drilled at high angle, to avoid directional drilling with sharp angles after setting a production casing at the top Dogger level. A 50-100m vertical depth range was targeted for the acoustic impedance to be predicted below the top Dogger carbonate aquifer. Despite the high frequencies emitted, the vertical resolution of intra-Dogger thin beds obtained by the VSP barely reached 10m, due to geological heterogeneities present in the propagation pathway. Besides, a Pilot Hole (PH) was drilled prior to the high angle leg to assess with full reliability the depth of productive thin beds to be subsequently drilled at high angle.

High Frequency (HF) VSP still represents a frontier seismic domain for which technical difficulties are piling up: *First*, the surface fix source should be extremely repeatable and preferably delivers an increased amount of HF energy to compensate somehow for the high loss of seismic amplitudes at high frequency.

*Second*, downhole receiver tool or toolstring may not present a consistent fidelity of 3 component reception over the whole recording frequency range, due to mechanical coupling characteristics of the VSP tool hardware and the open borehole ruggedness; in cased hole, the mechanical coupling of the VSP tool to the formation is insured by a good cementing quality between casing and borehole wall.

*Third*, the physics of the seismic attenuation depends on several factors, including viscoelasticity and heterogeneity, potentially variable in depth and laterally to the wellbore. Additionally, the geometrical spreading represents the main factor of amplitude decay, independent from frequency, and can be estimated at VSP processing stage.

Unexpectedly, the VSP image produced underneath the deviated hole section evidenced a faulted structure. Abrupt amplitude losses of high frequencies above 120Hz occur where the direct P-wave ray crosses one of the confirmed minor faults: it demonstrates that deeply buried formation rocks reworked by tectonic action drastically and preferably attenuate high seismic frequencies (Fig.1).

<figure><img src="image_2.png" /><figcaption>**Figure1:** Uneven attenuation of high seismic frequencies is evidenced by direct P-wave seismic propagation through faults and pre-faulted subsurface terrain, with increased ray inclination versus depth, independently from subhorizontal layering.</figcaption></figure>
Further details can be found online: https://doi.org/10.2516/stet/2024051

The attached presentation was delivered in the SPWLA-France Seminar on Geothermal Energy,
Friday June 28th, 2024: https://spwla-france.fr/events/

**Speaker short Bio:**

**Charles Naville:** Polytechnique-Paris 1973, ENSPM Engineer 1980, Geophysicist in CGG 1977-1989, field assignments in Gabon, USSR, USA, France. Geophysicist in IFPEN, 1990 to present. Experience in Surface seismic, reflection and long-range refraction. Borehole seismic / VSP & Full wave form sonic; VSP tool orientation; Drillbit SWD/RVSP; seismic integration.