Abstract

This paper provides a case history of the first hydraulic fracture on a subsea horizontal well in the Quissamã formation, a low permeability limestone reservoir, in Campos Basin, Brazil.

The well was drilled in the direction of the expected fracture growth, thus evolving longitudinal fractures along the horizontal section. It is part of a research project to evaluate selective stimulation methods for subsea horizontal wells. Every single aspect since the drilling, completion, and evaluation of the well, was done with the end in mind of hydraulically fracturing it in several stages.

Hydraulically fracturing a horizontal well has become a more accepted practice in our industry. The procedures used on fracturing of vertical wells must be taken into consideration when fracturing a horizontal well, to avoid re-fracturing work. Near-wellbore (NWB) problems are usually the main cause why fracturing work are not completed. This paper describes hydraulic fracture treatments with detailed discussion on analysis of calibration tests, fluid efficiency tests, and lessons learned.

Results of the pumping work will be presented showing theory and common practices played a key role for a successful application of techniques used. Laboratory tests are presented performed with cores taken from the well itself such, as rock mechanics, proppant embedment, compactation measurements, and basic mineralogy.

Production results will be presented and compared to conventional methods used on other subsea horizontal completed wells in Campos Basin.

Introduction

The main reservoir of Enchova and Bonito fields is the Quissamã Member of Macaé Formation. The Quissamã is a Lower Cretaceous, Albian age carbonate reservoir. The Enchova field is elongated southwest to northeast (Fig. 1), is in water depth from 106 m to 130 m and was discovered in 1976 drilling the well 1-RJS-22. The Quissamã carbonate is characterized by low to medium porosity (15–25%) and low permeability (1–10 mD), exhibiting a typical thickness of 40–70 m. The drive mechanism is gas expansion combined with some water influx of a weak aquifer. The undersaturated oil had an initial pressure and temperature of approximately 3550 psia and 190°F, respectively, with Rs value of 2750 scf/STB and a viscosity of 11 cP. The Enchova's Quissamã reservoir can be divided in three main groups: the south area, naturally fractured; the central area with lower permeabilities and porosities; and the thinner north area that had preserved the original porosities. The field came on production in 1983 and it is on primary production until today.

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