American Oil and Gas Reporter - April 2015 - 88

SpecialReport: New World Mexico
have improved reservoir characterization
and reserves estimation. For the Trion-1
well, preliminary estimates from conventional resolution tools resulted in a net
pay of 103 meters. After the petrophysical analysis that incorporated high-resolution, tri-axial resistivity and lithology
(from spectroscopy, which more accurately captured the rock's thinly laminated nature), the net pay was adjusted to 142 meters (a net pay increase of about 128 feet,
or 37 percent).
The left-hand image in Figure 5 shows
the evolution of the LWD sonic in the deepwater environment. The center image
shows a real-time LWD monopolar sonic
log and tandem BHA configuration. The
image at right shows a new generation of
LWD quadrupole sonic log in real time and
tandem BHA optimized, with the DeltaT
compressional and DeltaT shear sonic
logs from the LWD quadrupole sonic tool.
The process of identifying independent or compartmentalized reservoirs was
improved by using an in-situ fluid analyzer. Pressure gradient analysis is not conclusive if two sands interconnect. However, in situ composition and density data revealed a homogeneous fluid column in the
upper sand and a compositionally graded
bottom column, which clearly demonstrated that the two reservoirs were not connected, which assured clear flow consequences for future production.
Data processing techniques illuminated
subsalt structures, accurately defining surface seismic velocity information and
overcoming imaging challenges from shallow gas accumulations. Generalized surface
multiple prediction, a leading-edge algorithm, was used to remove the multiples
generated by the water bottom that could
mask underlying reflective events completely. High-end, prestack, depth migration
techniques were combined with anisotropic compensation for optimal seismic imaging and velocity model fidelity.
Advanced interactive velocity modeling that used localized seismic imaging allowed interpreters to modify the geometry of a salt body to obtain new depth-migrated images in close to real time, pro88 THE AMERICAN OIL & GAS REPORTER

FIGURE 5
Evolution of LWD Sonic in Mexico DeepAnd Ultradeepwater Environments
DeltaT
Compressional
22" Hydraulically
Expandable Reamer

22" Hydraulically
Expandable Reamer

181⁄8" SHO

171⁄2" SHO

Filter sub

adnVISION 8

adnVISION 8

TeleScope

sonicVISION 8

sonicScope 8

TeleScope

arcVISION 8
DTFA

COUL_MH

121⁄8"
Stab receiver
MXSL
MNSL

PowerDrive 900

COUL_NH

viding an advantage during salt interpretation scenario testing. Ray-based Q tomography also was used to mitigate the effects of shallow gas absorption, or other
similar amplitude attenuators.
Lessons from earlier Gulf projects
have shaped the evolution of Pemex's
deepwater operations. The subsea wellhead
has evolved to cope with very high pressure and significant loads that are created by long risers and sea currents (15,000
psi pressure and 7 million foot-pounds
bending moment capacity in the Perdido
area). The pump-and-dump method that is
used for riserless sections takes advantage
of specially weighted and engineered
drilling mud to improve hole integrity,
minimize geohazard effects, and provide
enough hydrostatic pressure to drill surface sections deeper for optimal casing setting depths.
The importance of maintaining verticality-achieved through specialized BHA
designs using RSS technology-when
drilling surface sections has been noted as
crucial for protecting against casing wear.
Drilling and under-reaming operations
must consider real-time data acquisition

arcVISION 8
121⁄8"
Stab receiver

DTCO_MH_RA

121⁄4" PDC Bit

Evolution Through Experience

DeltaT
Shear

PowerDrive 900
121⁄4" PDC Bit

(LWD/MWD) requirements in the drilling
assembly design, and hole size and wellbore quality must be addressed in the wireline evaluation program to allow optimal
data acquisition for reservoir characterization.
BHA designs were engineered as part
of a wellbore quality assurance approach
that maximized LWD and subsequent
wireline data acquisition and optimized cementing operations for zonal isolation.
Tandem drilling boosted deepwater performance and efficiency because it improved hole quality and allowed real-time
data acquisition. Accurately modeling
the complex and varied BHA designs has
proven central to ensuring reliability and
performance, as well as reducing shocks,
vibrations, torque and drag.
These best practice lessons were employed during exploration evaluation activities for the Perdido wells, with both
shallow and deep zones evaluated to
identify pay intervals and qualify expected reserves. In order to provide accurate volumetrics, physical rock samples
and fluid samples, the evaluation programs
have considered real-time data from wireline logging tools with tri-axial resistivity, elemental capture spectroscopy, nuclear
American Oil and Gas Reporter - April 2015

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