RIASSUNTO
Abstract
Operators have found that by integrating drilling and completion techniques, they can develop a highly reliable openhole horizontal gravel-pack completion that can control sand production and produce hydrocarbons at a high-rate. Because of the success of this methodology, it has become a mainstay completion technique in the deepwater developments in Brazil and has shown the same potential for upcoming deepwater developments in West Africa.
This paper will discuss the evolution of the integrated concepts, the ""lessons learned"" that are being used to increase the scope of application, and how new techniques are enhancing reliability for these completions. Specifics include advances that eliminate openhole tortuosity in openhole drilling techniques, new downhole tools that can reduce risk as well as completion cycle time, and improvements in gravel pack fluids.
These advances are continuing to push the technological envelope. The new technological benefits are:
Reduced completion cycle time, thereby reducing completion cost
Reduced formation damage
Improved completion reliability throughout the potential life of the well.
Introduction
Openhole horizontal gravel packing (OHHGP) has gained acceptance as a mainstay completion technique. Projected reliability and the potential to achieve significantly higher sustainable production rates have been the major drivers for pursuing this type of completion. Interval lengths in excess of 2500 feet are now fairly common, with the current record being 6,938 feet in a well completed in the North Sea by the Texaco North Sea UK Company.
In the early 1990's, the advent of enhanced drilling and fluids technology led to advances in extended reach and horizontal drilling.1,2 Screen only completions became the favored choice for completing in long openhole soft-rock formations in wells having capability to deliver high production rates.3,4,5 This technique is being successfully used in some areas including West Africa and the North Sea. But, as development moved into dirtier, more laminated reservoir sands and because of the huge variation in formation types, this completion method started experiencing high failure rates.6
The next move in development went from shelf to deepwater. This expansion into the higher cost operating environment inherent to deepwater further increased the need to improve completion reliability without impacting the desirable high-flow-rate capability. These drivers led to the development of the horizontal openhole gravel-packing technique and the state-of-the-art tools being used today.7,8
The ongoing improvements in drilling and drill-in fluids, filter cake technology, downhole tools and screens are enabling the application envelope for openhole horizontal gravel packing to continue to expand.
As with any new technology, there are still limitations. For example, a primary limitation is that the reservoir completed must have a sufficient spread between pore pressure and fracture gradient to allow gravel pack placement. Devices to lower equivalent circulating density (ECD) so that successful packing of longer intervals with tighter pressure spreads can be performed are now available. Invert gravel-pack fluids that eliminate the need to switch from an oil or synthetic oil-based system to a brine-based, solids-free, gravel-pack fluid are now being marketed. Further improvement in brine-based gravel-pack fluids has led to the development of an in-situ acid-generating fluid that should eliminate the need for a post acid treatment in injection wells and producers.
Drilling technology has been also been advancing, and bottomhole assemblies (BHAs) that can drill straighter holes that eliminate spiraling normally associated with conventional drilling assemblies have been introduced. These BHAs not only aid in hole cleaning but also in running the screen assembly to depth and achieving successful sand placement.