Performance Report: Integrated Wellbore Cleanup Enhances Productivity in California

Challenge: Traditionally, the operator would complete wells in this field by drilling the lower sections with oil-base mud, running the liner and displacing cement with lease water. After rigging down the drilling rig, a workover rig would perforate the production zone. Acid would be pumped to break down the perforations, the production packer would be set, the production string run and the lease water would be displaced out with nitrogen prior to stinging into the packer and beginning production. It was believed that production would be limited by residue from oil-base mud, cement, lease water and the lack of effort to remove them completely from the well.

Solution: M-I SWACO developed a fully integrated displacement program that included chemical spacers, displacement tools and filtration services. The goal was to remove all solids and emulsion residue that could reduce well productivity. Tools were selected to remove drilling-fluid solids and cement from the casing and liner in one trip. The spacer chemistry could efficiently remove the oil-base-mud residue and water-wet the tubulars in slightly more than one circulation. VIRTUAL COMPLETION FLUIDS (VCF) software modeled the hydraulics to size the spacers and ensure effective cleaning. Filtration equipment was selected to remove solids from the lease brine.

Result: The bottoms-up fluid sample contained 10% solids and oil residue. The lease water cleaned up 50 bbl (7.95 m3) after the viscous spacer returned with no solids or traces of oil. The well was perforated and acidized, the packer set, and the well was displaced from lease water to nitrogen prior to landing production tubing. This was the third well the operator cleaned using the M-I SWACO integrated displacement best practices and design. Each of these three wells exceeded the operator’s production expectations by sixfold. The operator contributes the higher production to the integration of M-I SWACO wellbore cleanup design and specialized tools.

Well Information
Location Elk Hills, California
Completion date August 2008
Interval displaced 7 ⅝-in. casing to 6,918 ft (2,108.6 m) and 5 ½-in. liner to 9,360 ft (2,853 m)
Workstring 2 3/8-in. tubing
Bottomhole temperature 238°F (115°C)
Completion type Cased and perforated
Mechanical wellbore tools used BRISTLE BACK Brush and RAZOR BACK Scraper
Fluid displaced 9.5 lb/gal (1.14 SG) VERSADRIL
Completion fluid used 8.5-lb/gal (1.02 SG) produced lease water

Once the lower sections were drilled with oil-base mud, the liner was run and cemented, and the cement was displaced with lease water. By the time the workover rig was in place, M-I SWACO had all the tools and fluids on location and ready prior to starting the displacement process.

The four poly tanks for storing spacers were manifolded together and connected to the rig pump. M-I SWACO had built the spacers at its plant and shipped them to the location in clean vacuum trucks. Frac tanks were placed on location to store clean lease water and to hold dirty lease water, contaminated spacers and interface returns from the well. The vacuum trucks that delivered the spacers hauled off the dirty lease water, contaminated spacers and interface. This eliminated an additional frac tank for dirty fluid. Prior to being pumped downhole, the fluid was filtered through a pod filtration unit.

The work string included the bit, 5 ½-in. M-I SWACO BRISTLE BACK Brush and RAZOR BACK Scraper tools near the bit, and a 7 ⅝-in. BRISTLE BACK Brush and RAZOR BACK Scraper tool near the liner top for mechanically removing drilling mud from the casing wall. The displacement spacers were pumped down the workstring. The workover rig could not rotate the string, but could reciprocate the pipe about 15 ft (4.57 m). Reciprocation started after the last spacer had gone through bit.

With the workstring at the bottom, the following spacers were pumped ahead of filtered lease water:

  • 20 bbl (3.18 m3) of base oil
  • 75 bbl (11.92 m3) of water treated with 2 lb/bbl (5.70 kg/m3) of DUO-VIS viscosifier, 6% by volume of SAFE-SOLV OM solvent and 3% by volume of SAFE-SURF O surfactant
  • 75 bbl (11.92 m3) of water treated with 6% by volume of SAFE-SURF O surfactant
  • 50 bbl (7.95 m3) of water treated with 3.0 lb/bbl (8.56 kg/m3)of DUO-VIS viscosifier
  • Followed by 8.5-lb/gal (1.02 SG) filtered produced lease water
  • Treat the first 100 bbl (15.9 m3) of 8.5-lb/gal (1.02 SG) produced lease water with one drum of FILTER FLOC agent to aid in filtration and minimize waste generated

Once the displacement began, pumping was continuous. After the spacers were pumped, the pod filtration unit filtered the fluid prior to its being pumped downhole at the maximum pump rate of 6 bbl (0.95 m3) per minute. This was equivalent to an annular velocity 158 feet (48.16 m) per minute in the 7 ⅝-in. casing. Dirty lease water, contaminated spacers and interface fluids were routed to the empty frac tanks.

Download: Integrated Wellbore Cleanup Enhances Productivity in California (0.47 MB PDF)

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