Triple Frac-Packing in a Ultra-deepwater Subsea Well in Roncador Field, Campos Basin - Maximizing the Production Rate

Abstract

The key issue to develop the Roncador field, located in ultra deep water offshore Campos Basin, in Brazil, is the maximization of production rate keeping the completion reliability, avoiding premature high workover costs involved in that scenario. Roncador reservoir has a succession of thick turbidite sandstones containing 31° API oil, requiring sand control and water injection to maintain reservoir pressures above saturation's. The distance between the pay zones are as short as 12 meters, becoming the first problem to fit the gravel assembly in such a short space. Flexibility in the completion is provided by an internal string with sliding sleeves. When water coning occurs in any zone, the sleeves shall be closed using slick line in a light workover. The paper will describe the main challenges to carry out three stacked frac-packs in a subsea well drilled in water depths above 1800 m, considering the experience acquired from the first three deviated subsea wells, working in dynamic positioned rigs. Special procedures were adopted to prevent failures during the completion, such as: rigid control of fluid cleanness and gel properties, selection and operation of service tools suitable to that environment (heaving, risk of rig drive-off) and careful design for frac-pack based on minifrac data. The drives for equipment selection will be reviewed, including the choice of perforation charges, gravel equipment and sliding sleeves. The good results obtained in those frac-packs, using the Tip Screen Out technique, reducing the skin effect compared to conventional gravel pack, will be presented too. Introduction Roncador field was discovered in October 1996 by the wildcat RJS-436. The 132 square kilometers field lies 125 kilometers off the coast of Rio de Janeiro, at water depths ranging from 1,500 to 2,000 meters (Fig. 1). The field size, the good quality of crude and the concurrent benefits for the downstream, allied to economic results of the project, led the Company to adopt a fast track development plan. In January 1998 another wildcat, RJS-513, confirmed the extension of the reservoir and the existence of oil in the southwestern portion of the reservoir. Immediately afterwards, Petrobras began the appraisal of the reservoir, drilling four other wells. In this same year the Early Production System (EPS) was designed to allow a long duration test in the wildcat RJS-436. Three major developments made this EPS viable: the Drill Pipe Riser2, the Guidelineless Christmas Tree with vertical production2 and the upgrade in FPSO Seillean3 to 2000 m water depth. The stacked frac-pack was deemed the solution required to obtain the desired flow rate in this vertical well, allowing long term appraisal with good economical results. In January 1999 the first oil came on stream in Roncador, when the Early Production System began producing through RJS-436 at a rate of 20,000 barrels of a light oil per day. This System is installed at 1,853 meters of water depth, being the current world record for a subsea completion. Background The wildcat well (RJS-436) was tested, indicating that sand control would be required. to develop the field. The sand control method planed was the frac-pack, defined here as the combination of fracturing the formation followed by an annulus packing. This choice was based upon two mean reasons:the excellent background of this method in Campos Basin andthe excellent results obtained in wildcat well by using frac-pack system. (i) Generally, Campos Basin sandstones are highly unconsolidated and have permeabilities ranging from medium to ultra-high values. In high permeabilities, damaging the well by sand controlling, no matter the method, is very common.

Frac Packing: Best Practices and Lessons Learned From More Than 600 Operations

“…This is the main reason that the hanging wall block of Roncador field was developed with three selective stacked frac packs. In fact, the need for this selectivity pushed the development of this technology that was first used in 1999 (Rovina et al 2000).…”

“…For a long perforation interval (more than 900 ft), the shrinkage of the blank pipe resulting from the thermal effect should be considered, and additional isolation packers should be installed (Rovina et al 2000).…”