Look Ahead Geosteering via Real Time Integration of Logging While Drilling Measurements with Surface Seismic

Abstract

Structural estimation capability ahead of the bit is evolving with innovative combination while drilling of borehole and surface data in real time. A pioneering workflow has been developed to recalibrate the reservoir structure via integration of surface seismic with synthetic seismic, derived from logging-while-drilling (LWD) measurements. Modern LWD services have nowadays reached a significant depth of investigation capability, expanding the horizons of geosteering applications. The most recent ultradeep azimuthal electromagnetic (EM) technology provides real time information on a cylinder of rock around the wellbore, up to 200 feet of diameter. This technology enables a new opportunity to update the pre-drill 3D geo-model with the measured local volume of information. Synthetic seismic, derived from EM measurements, is compared with real seismic data, using non-rigid matching to quantify the depth mismatch. The estimated displacement is then applied to the real seismic and to the pre-drill 3D geo-model repository (i.e. identified reservoir horizons, faults, and geobodies) to predict the structural setting of the reservoir ahead of the bit. It is possible to iterate through these steps using an automated process while geosteering. The workflow was tested on post-drill data acquired on an Eni well, recently geosteered within an oil reservoir consisting of fluvial and deltaic deposits of Triassic age. The automated interpretation tools, integrated on the seismic interpretation software, allowed building a pre-drill model in two-week time. The model provided a base for the creation of the geosteering roadmap considering the structural features potentially present along the planned trajectory. The real time simulation lasted two days in a play back mode, focusing on the assessment and validation of the workflow. Each process iteration took few minutes to provide results, validated in parallel with LWD available data. The calibration provided a robust dip and structure estimation and additionally the confirmation of fluid contact position, as identified in the pre-drill model. The workflow unlocked extra look ahead possibilities for optimal geosteering, and proved to be able to provide robust information 150m, on average, ahead of the bit. The presence of structural discontinuities was successfully validated within 30 m measured depth from the predicted position. This novel approach is a step further toward the possibility of providing accurate reservoir updates ahead of the bit, and so forth to improve well placement operations while updating 3D geo-models in real time.

A decision support system for multi-target geosteering

“…Bashir et al (2016) have explained how the formation tops in a 3D geo-cellular near-well sector model were adjusted in depth during drilling. In Arata et al (2017) a case study shows how a real-time local recalibration of seismic to minimize the depth discrepancy, based on LWD measurements, supports improved prediction of the reservoir boundaries ahead of the bit. Finally, in (Payrazyan et al, 2017) it is explained how the geological structures (faults and stratigraphic interfaces) in a 2D section along the well can be adjusted in real-time to fit the measurements, as basis for real-time sketching of a desired trajectory in the graphical interface.…”

“…To place a well precisely in the best reservoir zone, operators use geosteering to adjust the well trajectory in response to real-time information acquired while drilling. The benefits of geosteering, such as higher production rates of the resulting wells, have been extensively documented in the literature (Al-Fawwaz et al, 2004;Janwadkar et al, 2012;Guevara et al, 2012;Tosi et al, 2017).…”