Repsol Confirms Reserves in Unconsolidated Sands Offshore Mexico Using Intelligent Wireline Formation Testing Platform

Published: 03/05/2021

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Conduct reservoir testing and sampling in unconsolidated sands

Reservoir testing and sampling in unconsolidated sands presents many challenges. Repsol needed to collect representative samples in reservoirs with unconfined compressive strength (UCS) as low as 100 psi; test these reservoirs to ensure sufficient productivity potential; verify oil viscosities along depths in three, large-stacked sands; and assess reservoir vertical connectivity.

Perform DTT with ensured well control

Schlumberger recommended DTT using the Ora intelligent wireline formation testing platform. Its architecture features advanced metrology, tenfold-larger flow rate capabilities compared with conventional technology, and long flow times that help ensure safe well control while circulating produced hydrocarbons during the test. To visualize and design the test, a three-step simulation was conducted.

In other sands with similar flow capacity, Schlumberger recommended scanning and sampling fluids to inspect viscous grading. A combination of probes with third-party mesh filters mounted on the inlets was proposed to avoid sand production while mitigating plugging risks.

Understand reservoir productivity and viscosity profiles

Repsol safely conducted DTT, collected representative samples, and scanned fluid properties at four additional depths. During DTT, circulating active hydrocarbons avoided the need to perform a long test and flow to a barge for disposal of fluids at surface. The platform provided horizontal permeability (kh), vertical permeability (kv), and skin results to understand reservoir productivity, while downhole fluid analysis complemented with downhole constant composition experiments provided all fluid inputs required to model the fluids.

The results were evaluated analytically and numerically using Repsol’s static model, which was populated with acquired Ora platform fluid properties. This provided an understanding of the viscosity profiles seen in the stacked reservoir sands, productivity forecasts of the DTT layer, and minimum connected hydrocarbons in place.

"The deep transient test and fluid stations helped us collect clean hydrocarbon fluids in four different locations to determine the viscosity gradient and ensure economic flow potential. These results helped us confirm minimum reserves for our discovery offshore Mexico. This is the first time we used the Ora platform and will be looking at using it in our appraisals next year."

—Lorenzo Villalobos, Exploration Manager, Americas Repsol

Graphs showing three-step simulation using the Ora platform
Three-step simulation for cleanup (left), transient response (center), and well control (right) to define the optimal sequence to test the selected reservoir.
Graphs showing DTT pressure and pressure derivatives
DTT pressure and pressure derivatives showing a well-defined, infinite-acting radial flow followed by a change in mobility away from the near wellbore. This change in mobility was confirmed with two different buildups.
Log from well target and image of static model tested.
Well section of one of the targets showing input logs, rock types, and matched permeabilities with the DTT (left) and 3D view of the static model channel sands that were tested (right). This model was used to predict and history match the transient response.
Mexico, North America, Offshore

Repsol efficiently tested a thick reservoir offshore Mexico by using the Ora intelligent wireline formation testing platform’s deep transient testing (DTT) functionality, delivering high flow rates and produced volumes of hydrocarbons. Additionally, multiple fluid samples were collected along different stacked, loosely consolidated sands to accurately characterize the viscous gradient.

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