The Peregrino Challenge: How to Keep Reliable Models While Drilling Eight Wells per Year
Authors: Pettan Cassio , Stromsvik Jon Friis 
Published: June 2014

The frequent inclusion of all the latest acquired data into the static and dynamic models is a leading best practice for fields in the early stages of production. Since new decisions are taken continuously, it is clearly preferable to have reservoir models available that contain the most updated understanding of the subsurface.

Peregrino field is a sandstone reservoir, located offshore in the Campos Basin, with heavy oil characteristics and started its production in 2011. Nine wells were drilled in the first production year, seven wells drilled in 2012 and eight wells will be drilled in 2013. This involves a vast amount of new data being acquired both while drilling and during production. The data from the new wells needs to be made into information that can be used to improve well placement and the drainage strategy, always on time for the upcoming decisions. Also production data should be regularly considered in the model updating and used for history-matching, especially when new events like water breakthrough and pressure decline are observed.

This paper will give an overview of the methodology implemented in the Peregrino field in order to deal with these challenges. An integrated workflow has been used to keep the models consistent with new well observations such as structural tops, sand content and petrophysical properties and to ensure reservoir models updated on useful time. Also, new production data is being matched by updating uncertain parameters such as depth conversion, facies proportions, variogram lengths, oil-water contact, faults properties, relative permeability curves and KvKh, in a big-loop setup for history matching.

The final product of the methodology described is an ensemble of history matched reservoir models, created in a short period of time and using all the new data available. These models can be applied directly to calculate P10, P90 and mean profiles for new well locations, new projects or for updating the field production forecast. Considering the delivery time of these results and the solid structure of the workflow, the Peregrino field is ready for the challenge of keeping reliable models under the scenario of continuous information update.

Introduction

The Peregrino Field is located in Block BM-C-7, in the southernmost Campos basin offshore Brazil as shown in Figure 1. The area is located 85 km southeast of the nearest coastline, approximately 100 km southeast of Macaé. Statoil is the operator and holds a 60% ownership in the field while Sinochem is the sole partner holding the remaining 40% ownership.

Peregrino has large volumes of oil in place, over 2 billion barrels, in the currently developed area of the field, which are found in a heterogeneous sandstone reservoir. The reservoir interval is the Carapebus Fm., with good quality Cretaceous sands deposited from gravity flows in deltaic and shallow marine environments. The upper and lower parts of the reservoir are divided by a 5 meter thick siltstone flooding surface. The oil viscosity at Peregrino varies from 100 cP to 400 cP, and the average density is 14°API. This makes Peregrino one of the heaviest offshore oil developments in Brazil.