When revitalizing mature oil or gas fields, the ability to maximize productivity while minimizing operating costs is critical. Achieving these goals becomes more challenging where sand control is required. This is especially true for complex reservoir lithology, which leads to a variety of fracture and pore pressure gradients and premature water breakthrough. In addition, reduced deliverability, resulting from pressure depletion presents, additional complications related to achieving acceptable project economics.
The Barbara field, located in the central Adriatic Sea, is an example of this type of reservoir. For this project,a dedicated work team was assigned to identify and implement the solutions to improve field performance through continuous operations optimization. The Barbara field consists of stacked pay sections that have been depleted since the early 1980's. To achieve favorable economics, techniques had to be used that would both maximize the deliverability of each well and minimize operational costs.
This paper reviews the Barbara field workover program. The evolution of techniques, equipment, and products leading to enhanced productivity while substantially reducing costs is described. The fluid systems and operation procedures designed to optimize frac-pack geometry are discussed. In addition, the one-trip multi-zone gravel pack assemblies are described that allow multiple zones to be individually frac packed in a single run, thus providing significant rig-time reductions without sacrificing completion efficiency. Finally, the complex nature of this reservoir dictates a need for avariety of completion techniques. This means that fracpacking was not necessarily an option for all zones. For the intervals where fracturing was not employed, productivity still needed to be maximized. To accomplish this goal, perforation tunnel clean up procedures have been optimized.
The Barbara field is situated in the Adriatic offshore area approximately 30 km from the coast. The field produces gas and consists of some 40 productive layers which have been identified at depths between 1000 and 1300 meters. The permeability ranges from a minimum of 5-10 mD to a maximum of 500-600 mD. The reservoir sands are composed of sediments of the Asti formation which were deposited in the Pleistocene period in a turbidite environment, the cap rock is formed by several argillaceous intercalations. Multizone completions are necessary for efficient reservoir management. Experience indicates that these unconsolidated sands require sand control.
The exploitation of the Barbara field started in early 80's. In less than 7 years the field was completed with over 100 well in dual, multi-selective, sand control completions. In late 90's however due to subsidence phenomena most of the higher producing layers saw a dramatic drop in production performances.
To aid in restoring productivity, a major workover program was conducted between 2000 and 2003 on the platforms "F" and "C" of the Barbara field. The original project scope was only 11 wells. However, the unexpectedly good results led to this project being expanded to a total of 77 completions in 6 wells.
Gravel packing has been extensively used to control sand production in new wells and during workover operations at Barbara.
