A large number of fields worldwide have sand production problems and a common solution is a gravel pack (GP) completion. Over time this GP can become plugged with production fines as well as solids that may precipitate out of the produced fluids. As the GP plugs, it creates a larger restriction to flow and the production rate will decline. At some point the operator will decide the production rates are no longer acceptable and intervention is required. As a result, the GP completion will either be pulled from the well or be cleaned in-situ.
Previous in-situ cleaning processes involved treatment fluids bull headed into the well or placed by coiled tubing, to dissolve GP plugging damage.
This paper describes a new method for cleaning a GP in-situ. The process involves a rotating jetting head to create specific pressure pulsations combined with angled nozzles to create a "circulation current" within the GP. These circulation currents are localised and result in a temporary increase in GP permeability ensuring that treatment fluid will invade the GP only in the area immediately adjacent to the tool. This new process is significantly more efficient at unplugging the GP than previous methods and treatment fluids can more effectively reach areas of the completion such as the perforation tunnels and drill-in fluid filter cake damage. This process also includes managing the jet impact pressure to ensure that fragmentation damage of the GP proppant does not occur.
The paper will report results of laboratory tests using existing wash methods compared with the new technique and demonstrate the differences in; treatment fluid placement efficiency, fines removal efficiency and damage caused to the GP proppant.
GP completions act as a filter to limit sand production in thousands of wells worldwide. As time goes by the GP can become plugged with the fines it is filtering as well as the solids that precipitate out of the production fluid. These fines choke off production until remedial action is taken to remove them. This action usually takes one of two forms, pull the completion or use reactive fluids to dissolve the fines and remove them in-situ.
Pulling the completion can be expensive, entails risk and involves killing the well, so it is typically the last option considered. Using reactive treatment fluids, such as acids, to clean the GP has been done in the past with varying degrees of success. The actual chemical formulations used to dissolve the fines have been studied before in papers such as "An Economic, Field Proven Method For Removing Fines Damage From Gravel Packs"1 and are not investigated in this paper. The research in this paper focuses on the delivery method of the treatment fluids and the potential use of hydraulic energy to remove fines that may not be soluble.
In the past, treatment fluids were bull headed into the GP or placed with coiled tubing.
Bull heading refers to the pumping of treatment fluids directly down the production tubing or workstring. Although this method may seem to be the easiest operation, there is a risk it will be ineffective because of poor placement of treatment fluids and the corrosion dangers associated with pumping corrosive fluids down the production tubulars. When bull heading, treatment fluids will take the path of least resistance. Once they exit the tubing there is no guarantee where this will be, even if diverters are used. To overcome this inefficient bull head placement issue, high fluid treatment volumes are often used, creating a costly design and the risk of over treating one section of the GP while possibly under treating other sections. A more effective alternative to bull heading is often sought.