Polymer-free viscoelastic surfactant gravel-pack fluids
Reduce formation damage and enhance gravel-packing efficiency with polymer-free fluids.
An operator was developing a field along the coastline offshore Southeast Asia. Targeting this marginal oil required drilling into multiple hydrocarbon prospects with stacked shale and water zones. Drilling the wells from offshore was deemed uneconomical. Accessing the oil from land wells that tied into existing onshore infrastructure would be more efficient and allow immediate production.
The company planned an openhole “fishhook” well with an upward trajectory of up to 136°. The openhole interval was to be more than 700 m long and have six zones. Gravel packing had to be accomplished at the steep angle without exceeding the fracture pressure. The upward trajectory would make it difficult to keep the proppant from sliding and bridging in the wellbore, which would prevent a full annular pack.
To mitigate the bridging and promote heel-to-toe packing, Schlumberger recommended an innovative gravel-packing system that would minimize friction pressure during the operation and help ensure a full annular gravel pack in the challenging environment.
A screen completion string, designed to accommodate six zones, included five oil-swellable packers to isolate the zones in the openhole interval. A sixth oil-swellable packer was placed inside the casing above the top of the screen to provide a bottom for the pack and to encourage heel-to-toe packing from inside the casing shoe. These fast-acting swellable packers were soaked in a diesel oil that allowed the elastomer to swell against the openhole rock before the zones were gravel packed, isolating the zones and preventing the pack from sliding downhill during gravel packing.
Pressure-activated diverter valves incorporated into the internal service string were evenly spaced along the openhole section to minimize the circulating pressure exerted on the formation during the packing operation. These valves short-circuited the washpipe at various locations, shortening the length of the washpipe through which the returning gravel-pack carrier fluid had to travel.
The system included the OptiPac Alternate Path openhole gravel-pack screen, which has shunt tubes to prevent bridging. The shunts diverted slurry accumulations into the zones between the packers until the annulus was fully packed. Transport and packing tubes delivered slurry to the area between the screens and the wellbore. This design reduced slurry dehydration inside the shunts, eliminating the risk of bridging into the tubes and extending the potential length of the gravel-pack interval.
The Hornet skid-mounted gravel-pack blender was used to optimize delivery. The ClearPAC fluid was chosen as the optimal gravel carrier fluid because of its capabilities to reduce friction and suspend the gravel at low shear rates. The viscoelastic gel also helped control leakoff through the nozzles of the packing tubes.
The antiswab washdown service tool stabilized the hydrostatic pressure in the open hole, eliminating the swabbing effects of hardware movement and ensuring filtercake integrity before gravel placement. After the excess gravel was screened out and reversed, the service tool allowed spotting of filtercake removal treatments, eliminating a dedicated cleanup run.
The combination of technologies resulted in a 100% gravel pack below the fracture pressure of the well. Accessing the well from an onshore location enabled the operator to reduce the costs and risks related to offshore operations. As a result of this success, 10 additional fishhook wells, both injectors and producers, were completed along the shore. This new completion design provides an alternative method for gravel packing fishhook wells with narrow frac/pore-pressure windows and developing hydrocarbon prospects in shallow waters from onshore drilling locations.
“I would like to congratulate the team for achieving a 100% gravel pack. With 731 meters of screens, the well had the longest uphill gravel pack with Alternate Path screens to date. The team has obviously set a world record.” —Production Engineer
Challenge: Find an efficient way to develop offshore hydrocarbon prospects and control sand production in shallow-water fishhook well from onshore drilling location.
Solution: Design a gravel-pack system specially suited for wells with fishhook trajectories with the following technologies:
Results: Achieved a full annular gravel pack in the inverted-angle well with zero sand production; successfully met production and injection targets.