The completion of long horizontal intervals is a challenge faced by Petrobras since the discovery of heavy oil offshore fields in the 80's. The gravel-pack completion is a well know technique applied successfully in hundreds of offshore wells in the Brazilian coast. Besides, the operational limits are frequently very tight, once the water depth has been increased, as well as the desired open hole length. Due to these facts, the pressure gradient is very close to the pore pressure and the gravel-pack setting is the most critical operational step. The gravel transportation by the fluid requires a flow rate that can result in friction losses that can increase too much the bottom hole pressure resulting the formation fracture.
The use of drag reducers is an alternative to perform, the operations in deep water scenario with long wells, as they can lower the bottom hole pressure during the fluid flow. This work aims to present the selection, laboratory and large scale loop tests of nanostructures well known as worm like micelles, used as drag reducers. The main advantage of these structures when compared to conventional drag reducing agents is its capacity of self-assembling. The long nano-structures can resist to pumping displacement, pipe transport as well a contact with solids. It was also evaluated the possible damage of use of wormlike micelles into sand reservoirs, showing they are a real option to perform gravel-pack completion in critical scenarios.
The gravel-pack operation is a well completion technique generally used in unconsolidated formations. The main objetive is to avoid the production of formation constituints and consequently increase the well completion reliability. It consists in filling the annular space between the formation and a set of screens with sand or ceramic particles that acts as a filter to retain sand from the formation during well production.
The gravel-pack operation performed in a horizontal well can be divided into three distinct stages. The first stage consists in pumping the water/gravel through the work string and gravel tool, where the flow is diverted from inside the column to the annular space. In the second stage (alpha wave), occurs the gravel grains deposition due to decrease in flow velocity, spreading a bed of gravel with relative height (ha) until the end of the well and leaving a free channel between the upper open hole and the top of the bed. After propagation of the alpha wave, starts the third phase (beta wave). In this stage the particles begin to deposit over the bed, filling the upper open channel, as shown in Figure 11.