Offshore/subsea systems

Sapinhoá Field, Santos Basin Presalt: From Design to Execution and Results

This paper presents the development of Sapinhoá field, covering the fast-track transition and decision-making process, from appraisal to conceptual and basic engineering of the Sapinhoá pilot project and on to its subsequent execution, highlighting the challenges, lessons learned, and results.

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This paper presents the development of Sapinhoá field, covering the fast-track transition and decision-making process, from appraisal to conceptual and basic engineering of the Sapinhoá pilot project and on to its subsequent execution, highlighting the challenges, lessons learned, and results. Even though, at the time, several uncertainties about developing presalt areas were present, a fast-track strategy was chosen. A pilot project was seen as a means to provide valuable information for the remaining development of Sapinhoá and other fields in the presalt cluster.

Introduction

The Sapinhoá field is in Block BM-S-9 at the central portion of the Santos Basin (Fig. 1). The water depth is approximately 2140 m, and reservoir depth lies between 5000 and 6000 m, with salt-layer thickness up to 2 m.

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Fig. 1: Sapinhoá Field and Santos Basin presalt cluster.

 

The main objectives of the Sapinhoá pilot were to evaluate the production and injection behaviors in a carbonate reservoir of microbial origin and obtain information and provide technology development so that those could be used for the remaining development of the presalt cluster. This information would be ­useful to

  • Define the best recovery method to be applied in future projects
  • Define the best exploitation strategy
  • Optimize location, geometry, and number of wells
  • Evaluate reservoir hydraulic communication
  • Estimate vertical and horizontal permeability

Project Engineering: Concept Overview

Production-development plans consisted of the installation of a chartered floating production, storage, and offloading (FPSO) vessel in the field’s south area; a well-construction campaign; a subsea gathering system; and gas-export-­pipeline installation.

Well System. Well design for the Sapinhoá pilot had to take into consideration requirements from other disciplines, which affected final configuration, including the following:

  • Scaling precipitation risk, which was mitigated through inclusion of a downhole chemical-injection mandrel
  • Number of permanent downhole gauges (PDGs) per zone, to manage the reservoir better
  • Remote selectivity of the producing/injection zone, achieved through the selection of hydraulically operated control valves
  • Lithology uncertainties, mitigated by the use of large-bore wellheads, allowing an extra casing string without affecting production-casing diameter

The project final scope consisted of 11 wells—six producers, one gas injector, one water-alternating-gas (WAG) injector, and three water injectors that later could be converted to WAG injectors if necessary.
As for completion design, intelligent completion was the primary choice, followed by single-zone completion, depending on the number of intervals found. All wells had a 6⅝- and 5½-in. combined production string, in order to cope with the expected high flow rates. Acid stimulation was considered for all wells, not only to achieve the maximum flow rate but also to guarantee that the production or injection profile would be close to the simulated distribution. Smart wells included PDGs, chemical-injection mandrels, and hydraulic valves below the feedthrough packer.

Subsea Production System. The development of a subsea production system for the Sapinhoá pilot was challenging. The carbon dioxide and possible hydrogen sulfide presence affected material selection for equipment and pipes in multiple ways because special alloys have longer lead times to delivery and required qualification of material and welding process. The 2000-m water depth, combined with metocean data that indicated a harsher environment in Santos Basin than in Campos Basin, posed a problem to riser design and installation. Finally, reservoir pressures and the requirement to inject gas demanded a highly resistant gas-injection line.

A buoy-supporting-riser (BSR) concept was considered the alternative with the best economics after technical-­viability verification. The decoupled BSR gathering system was a new riser concept featuring a tethered buoy, measuring 52×40×10 m, which is submerged approximately 250 m and has 22 to 28 risers connected to it, including steel catenary risers (SCRs) for production and injection purposes, flexible lines for gas lift, and electric/hydraulic umbilicals.

The remaining architecture of the subsea system included satellite production wells connected individually from each pipeline end termination to its respective tree through flexible flowlines and a vertical connection module.

Flow-Assurance System. The main concern regarding flow assurance for the Sapinhoá pilot was the possibility of scaling precipitation in the production string. To mitigate this risk, it was recommended that all wells be stimulated to full capacity because smaller drawdowns reduced precipitation. Downhole scaling-inhibitor injection also was necessary because the precipitation normally occurs at the largest-differential-pressure point, which is the transition between the reservoir and the well.

FPSO Vessel. The FPSO vessel Cidade de São Paulo was converted from a double-sided single-bottom vessel in China, with the process modules being constructed at different sites worldwide and integrated at Brasfels shipyard in Brazil. The process plant has overall capacities of 120,000 B/D of oil, 150,000 B/D of liquid, 150,000 B/D of water injection, 5 000 000 m3/d of gas production, and 3 250 000 m3/d of gas export.

Project Strategies: Dealing With a Fast-Track Execution

Because of the fast-track guidelines adopted for this project, the project scope began being defined at an early stage. Strategies were needed that could guarantee some flexibility for the project, ­allowing for changes in the future.

Well-Construction Campaign. The strategy adopted for well construction was to charter three rigs to be dedicated to all projects of the block, including the Sapinhoá pilot. With dedicated rigs for the project, it was possible to specialize each of them in certain activities and, consequently, optimize the wells campaign, reducing time for each activity.

Subsea Equipment. Because of the scope uncertainties and the long-lead-time supply for subsea equipment, the presalt tree standard was defined as a unique model that could be used for producers, water injectors, gas injectors, and WAG wells. That way, the order could be made even if the scope or sequence of well construction had not been fully defined.

FPSO-Vessel Construction. The Cidade de São Paulo process plant was designed so that it would be able to receive different kinds of fluids and to deal with different recovery methods in the future.

Project Execution: Results and Lessons Learned

Reservoir Results. The drilling results confirmed the expectations for the Sapinhoá field, presenting excellent productivity and injection. The initial-­production potential flow rates are ranging between 29,000 and 36,000 B/D, surpassing conceptual-design estimates of 25,000–30,000 B/D.

Wells Campaign. The Sapinhoá pilot well-engineering program had to deal with uncertainties and challenges from a technical point of view and from the ­imposed fast-track approach.

Despite this environment, the Sapinhoá pilot well-construction-campaign costs and schedule performance were reduced significantly during its execution because of an accelerated experience curve. At the basic-engineering phase, the campaign duration was estimated to last 2,368 days. It is now projected to take 1,997 days, a 15% reduction.

Subsea System. Because of the fast-track implementation and the innovative aspects related to the presalt subsea equipment, the first deliveries suffered delays, mainly with regard to the trees. To deal with that, the project team had to review its well-campaign schedule continuously, postponing some well completions and anticipating the drilling of new wells.

At the end, those delays had no direct effect on the project ramp up because the wells campaign was executed faster than planned.

Conclusion

In spite of all the challenges and risks envisioned at the conceptual phase, the Sapinhoá pilot managed to become a successful project, both technically and economically. Approximately 1 year after the field’s declaration of commerciality, the production unit was already operational, and, 2½ years after startup, oil production is at peak.

In order to deal with the complexity and uncertainties of the reservoir, combined with the fast-track implementation, the project conception and development strategies needed to be based on two pillars: flexibility and robustness.

Flexibility. This was applied, for example, in different possible recovery methods, number of wells, well-construction configurations, contingency plans for subsea activity, and different FPSO operation methods.

Robustness. This was applied, for example, with tree specifications, metallurgy selection, and wellhead and casing design.

The continuous search for and implementation of flexible and robust solutions were key success factors of the project, enabling the management team to deal with design and execution changes as they appeared, keeping the project optimized.

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 26320, “Sapinhoá Field, Santos Basin Presalt: From Conceptual Design to Project Execution and Results,” by J. Turazzi Naveiro, SPE, and D. Haimson, Petrobras, prepared for the 2015 Offshore Technology Conference Brasil, Rio de Janeiro, 27–29 October. The paper has not been peer reviewed. Copyright 2015 Offshore Technology Conference. Reproduced by permission.