Challenge

The field consists of massive,homogeneous marine turbiditesandstones with excellent reservoirproperties; however postdeposi-tional faulting and deformationresulted in highly deformedreservoir boundaries. These fea-tures complicate well placement.On some wells, more than 33% of injection shales were crossedon the horizontal section, affect-ing borehole stability and impact-ing well production. The primaryobjective was to develop theresource safely and with the leastnumber of wells.

Solution

A reservoir heterogeneity studywas conducted over the field to understand the shale and thesand injection distribution, basedon the combination of four com-ponent and Q-Marine* surfaceseismic data.

Results

The results of this study encour-aged the use of specialized tech-nology; for example, an ultradeepresistivity LWD tool was partic-ularly useful in addressing thespecific challenges of the field.

Reservoir Heterogeneity Study Improves Well Planning Efficiency Case study: Reduced drilling risk with 3D surface seismic data

Steering in complex sandstone formations

The field under study consists of massive, homogeneous marine turbidite sandstones

with excellent reservoir properties. The reservoir is located in a Tertiary formation,

providing stratigraphic traps consisting of massive, medium-grained, homogeneous

turbiditic sandstones and enclosed by shales. The deposition and geometry of the

turbidite sand lobes were primarily controlled by the original basin morphology, which

forced the sand to deposit along a main axis parallel to a structural high.

The postdepositional faulting and deformation resulted in highly deformed reservoir

boundaries, where shales have been squeezed into the sand and sand has been injected

into the overlying shales in the form of dikes and sills. These features complicate well

placement and make it even more important to steer the wells accurately. On some

wells, more than 33% of injection shales were crossed on the horizontal section, affect-

ing borehole stability and impacting well production.

3D seismic facies analysis

A reservoir heterogeneity study was conducted over the field to understand the shale

and the sand injection distribution, based on the combination of four component and

Q-Marine surface seismic data. The results of this study encouraged the use of special-

ized technology, for example, an ultradeep resistivity LWD tool was particularly useful

in addressing the specific challenges of the field.

Heterogeneity mapping confirmed the shale injections at the well location.

Geology

Case study: Reduced drilling risk with 3D surface seismic data

In this field, the turbidite

sand lobes have undergone

syn- and postdepositional

deformation generating a

complex geometry of the

main reservoir sands. This

geometry is characterized

by a shale streak coming

from beneath the reservoir

and sand injectites distrib-

uted above the reservoir and

on both margins of the main

sand lobe.

The general inversion

scheme involves 3D seismic

facies analysis, which is

a powerful quantitative technique derived from seismic stratigraphy. Seismic facies are

groups of seismic reflections with parameters such as amplitude, continuity, reflection

geometry, and frequency. These are distinct from adjacent groups.

This approach consists of a 3D classification of the seismic texture attributes using

a proprietary algorithm. The geological derivation of the classes is determined by investi-

gating the character of the seismic data and the lateral-vertical associations of seismic

facies, using well calibration and rock physics analyses.

The heterogeneity classes are extracted as a 3D geobody and sampled as a grid. The

geobody grid is populated with rock physics properties, which add a qualitative measure-

ment to the heterogeneous bodies. 3D geobodies include a risk scale that converts the

classification results into a 3D drilling risk map.

Well planning process improved

The primary objective of asset teams is to develop the resource safely and with the least

number of wells. Predrill seismic assessment of drilling hazards has become an essential

part of the well planning process. 3D reservoir heterogeneity mapping leads to a better

understanding of the geometry of the reservoir interval and increases the efficiency of the

well planning process.

E-mail dcs@slb.com or contact your local Schlumberger representative to learn more.

06-DC-011 November 2006 *Mark of SchlumbergerCopyright © 2006 Schlumberger. All rights reserved.Produced by Schlumberger Marketing Communications

www.slb.com/dcs

Optimizing well placement with a 3D risk map.

3D distribution of the seismicfacies derived from classifica-tion of seismic texturesabove the main sand lobe. Red denotes the potential sandinjectites. Log data from thewells confirmed the presence of remobilized sands.

Shale injections mapped as V-shaped features on the seismicdata. On some wells, more than33% of shale injections werecrossed on the horizontal section.