Innovative Adaptation of Sub-Sea Test Tree Successfully Tests Ultra Deep-Water Wells in the Campos Basin, Brazil
Authors: Etcheverry Carlos Fulvio , Tigre Maia Claudio R.F. , Wendler Curtis 
Published: October 2008

Testing and gathering data from a well to evaluate the potential of a new field is a common practice in the oil and gas industry. However, performing this task in a subsea environment to test a well in ultra deep water presents significantly greater challenges to the operator and service providers. Since testing in the depths required for the subject well had not previously been attempted, there were concerns of problems that might occur in maintaining response times and control of the test equipment.

This paper will present the innovative solution that was devised to perform the evaluation testing in the deepest offshore producing well in the world (1,853 meters or 6,079 feet) from a drill ship with conventional subsea equipment. The equipment, the well, location conditions, and procedures that were used to safely and efficiently perform the evaluation testing will be discussed.

To date, this has been the deepest well in which this function has been successfully performed. From the well testing data gathered, the Petrobras Reservoir Engineering and Geology Departments were able to determine production potentials, which indicated that this was the most important discovery of the last few years, as well as to obtain information that would be invaluable for field development. It is anticipated that the field will have an estimated oil production of 180,000 BOPD and 4.8 mm m3 of gas by the year 2,000.

Introduction

Industry experience has identified a number of issues related specifically to deep water testing operations that require careful wellbore analysis according to prevailing conditions and environment. These issues will vary from well to well, and therefore, it is of critical importance that they be analyzed on an individual basis. Major points of concern in this case were:Procedures for disconnect and reconnection or shear.Alarm philosophy.Response times.Confirmation of shear ram capability to cut handling subs.Subsea test tree (SSTT) response after shear.Retainer valve selection.Chemical injection points and rates.

73% of the Brazilian oil and gas reserves are in deepwater (300 m to 1,000 m.) and ultra deep water (above 1,000 m.) fields in the Campos Basin area. Also, it has been estimated that over 60% of the future oil discoveries will be found in deep and ultra-deep waters in the same location. These facts show that the production of deep- and ultra-deep-water fields is a vital issue for Brazil and its operators and explain why it is critical that the challenges of testing and production be met.1

After the discovery by Petrobras of two giant fields in the Campos Basin, Albacora (1984) and Marlim (1985), in waters from 200 m (656 ft) to 2,000 m (6,560 ft), the need to test the exploratory wells presented many challenges and questions. Since the wells were exploratory, should the testing be done from a drill ship or semi-submersible rig (normally the methods of choice in this area), and how could the testing be done safely?