The 6 1/8” section is drilled as high slanted 84º in lower reservoir to get more exposure with production zone. After drilling, pressure points were taken to design completion fluid along with roller reamer to make sure hole is smooth. Production / plugging screen test (PST) is performed for the Reservoir Drilling Fluid (RDIF) prior to run ICD (Inflow Control Device) screens to make sure that, solids present in RDIF should not plug screens.
Passing PST is also concern when high-density fluid is used due to shale stability at high inclination. Time required to pass PST depends on following factors.
Selection / Type of RDIF
Water based mud will have low solids as compared to NAF (no-aqueous fluid) due to base fluid density. Solids % depends on type of salt used; high-density brine (KCOOH, CaBr2) will have less solids in WBM (water-based mud) as well as NAF.
Type of weighing material used (CaCO3, manganese tetra oxide, etc) also affect total solids hence PST time.
Solids % in RDIF
Time required to pass PST for high density fluid will be more as compared to low density fluid. Solids % also depends on Oil Water Ratio (OWR) for NAF, lower the OWR, less are solids due to brine phase salinity & weight. 70/30 OWR will have lees solids as compared to 95/5 OWR. Drilling solids also come into the system while drilling, which affect PST time. It is very important to have all solids oil wet in NAF to avoid aggregation of particles hence increase rheology.
Particle Size Distribution (PSD) of RDIF
RDIF is weighed by using CaCO3 however 20-30 ppb sized CaCO3 is added while drilling for effective bridging on the basis of pore throats. It is very important to have PSD for Weighing material below ICD screen opening (~ 53 micron) to avoid screen out which results in drop in density.
Time exposure from drilling till PST
Sized CACO3 used for bridging will be utilized to plug pore throats, some will be grinded and some will be screened out from shale shakers depends on size of particles and shaker screen size used while drilling. Circulation & reaming time also help to grind size CaCO3 & discard un-wanted solids. Long section required more drilling, circulation &reaming time hence, it helps to grind more sized CaCO3.
Efficiency of shale shakers to handle flow while drilling and conditioning RDIF. Shaker screens size dressed to remove un-wanted solids. Time since finer screens are dressed.
Drilling cuttings & un-wanted solids stick / aggregate in Ditch / Flow Line, possum belly / header box, below shale shaker area & active mud tanks. If these areas are not cleaned so it will be mixed in RDIF again hence won’t be able to pass PST.
Loose sand washed out while reaming & circulation for PST, which will delay to pass PST. Drilled solids & RDIF additives may accumulate or form bed at the top of 7 inch liner, which can’t be cleaned with same flow rate as used in open hole due to low annular velocity.
Recommendations To Minimize Time Required To Pass PST
- Solids Control Equipment’s (SCE) and the availability of the required original shale shaker screens should be checked on rig site by calling expert engineer.
- Active mud should be circulated offline over shale shakers while tripping to discard un-wanted solids to minimize time for PST.
- When screening out bigger particle size (bridging or weighing material) for PST, to avoid a drop in fluid density, only fine CaCO3 (5 – 50 micron) / weighing material should be added to maintain density required for well-bore stability.
- It is recommended to circulate with high flow rate (~ 325gpm for 6.125 inch) & rpm (~130 – 140 ) at bottom as well as top of 7 inch liner to clean sand accumulated because of high annular area.
- Sand Trap, Ditch / Flow Line, Possum Belly / Header Box, below shale shaker area & active mud tanks should be cleaned either while POOH after TD or while RIH with pressure point assembly along with roller reamer.
- It is not recommended to rotate string while circulating for PST, which can produce fines and affecting PST. Hence reciprocate only to avoid stuck pipe.
- It’s not Recommended to weigh up NAF with size CaCO3 (above 53 micron) as well as high concentration of bridging agent else it won’t pass PST (screen size ~ 53 micron) unless particles are grinded enough while drilling & circulation. This may lead drop in mud weight due to screen out larger particles from shale shaker while circulating for PST.
- For heavy mud weight weighed up with CaCo3 (above 11.6 ppg), it’s recommended to use manganese tetra oxide (weighing material ) in combination of CaCO3 having particle size in the range of 2 – 5 micron. It’s recommended only for heavy NAF weighed up with fine particles.