Food manufacturer, Lincolnshire
This case study details a project undertaken by the company to drill a 720mm borehole for a food processing facility. WB+AD Morgan were employed to rectify the issues and successfully drilled a new borehole to pump 120m3/hr
Original borehole produced large volumes of suspended solids when running at a high yield. This was probably caused by the original construction not isolating the soft and poorly consolidated strata that sits above the Lincolnshire Limestone. The borehole also had an artesian head at surface (flowing artesian) in excess of 80m3/hr and 0.5 bar.
To maintain control of drilling fluids and the artesian head, the borehole was drilled using rotary mud flush and a casing preventer at surface. The site would have flooded if there were no preventative measures in place to control the artesian flow.
– Starter casing set at 810mm diameter to 2m depth
– Drilled diameter at 720mm to 18m depth and 508mm diameter steel casing pressure grouted into position
– Drilled diameter from 18m to 55m at 485mm and 406mm diameter steel casing pressure grouted into position
– Drilled from 55m to 84.5m depth at 400mm diameter
– Cased with 304mm uPVC casing and screen
– Geology: Lincolnshire Limestone
After drilling, borehole was developed with 20% Hydrochloric acid to improve yields.
Following successful completion of drilling and initial yield test, acidisation has improved both the yield and borehole performance, thus running costs for the factory are reduced. Borehole pump now has capability to pump at over 120m3/hr (33L/sec).
Textile company, near Mansfield
760mm diameter to 85m deep
Cased to 28m with steel casing – open hole below
Pumping rates of 56m3/hr
Geology: Sherwood Sandstone
Dirty water during borehole pumping. Investigation using CCTV showed borehole wall had collapsed at depth, possibly caused by ground movements due to historical coal mining activities.
Work carried out:
– Remove existing pump and old steel riser pipe
– Clear borehole using airlift eductor technique
– Install new casing string using Bridge Slot Carbon steel screens at 406mm
– Install 3-8mm gravel pack to stabilise borehole wall
– Develop borehole using airlift to settle gravel pack
– Install pump on new PVC rising main
– Carry out step test to check borehole performance.
Water runs clear after borehole pump is turned on – pumping rate of 60m3/hr with minimal drawdown shows that borehole is still hydraulically efficient.
Public supply borehole, West Sussex
400mm diameter to 51m deep
Cased to 12m with steel casing- steel screen to base of borehole with 3mm slot
Sand pack behind well screen 5 to 10mm
Geology: soft sands and bands of sandstone
Borehole pumping sand, infill at the base of the borehole. Investigation using CCTV showed that a hole in the flexible rising main, caused by torque twist, had punctured the well screen via the high velocity jetting action. This allowed the sand pack and soft sand from the formation to flow into the borehole.
Work carried out:
– Fabricate hydraulic (water only) casing “punch” to perforate the existing well screen allowing the remaining sand pack to flow into the screen.
– Remove remaining sand pack via an air lift eductor system and store for future use.
– Remove damaged well screen and install new stainless steel wedge wire screen and re-introduce the collected sand pack.
– Develop borehole to settle sand pack and re-install pump on a new rigid riser pipe.
Borehole now back in supply
Paper mill, Kent
406mm diameter to 78m
Cased to 35m with steel casing
Stainless steel screen to base of borehole with 1mm slots
Geology- Folkestone and Hythe beds (Lower Greensand)
Borehole pumping suspended solids and reduced borehole performance
CCTV of borehole by EGS which indicated that the borehole screens were partially blocked with encrustation from iron bacteria and manganese deposits.
Turbulent inflow of water towards the base of the borehole.
Chemistry analysis of the water showed that there were high iron and manganese levels.
Work carried out:
– Mobilise workover rig to site
– Remove existing pumps and riser. Clean pump in “acid bath ” to remove any blockages on intakes etc.
– Scrub borehole walls and screen section using purpose built scrubbing tool
– Backfill a section of the borehole base using clean inert silica gravel and install fabricated concrete “plug” 1.5 long to hold gravel backfill in place
– Develop borehole by using airlift eductor methodology to minimise potential ingress of air to the system. Flush borehole with Clearbore product to remove any remaining iron/manganese build up.
– Carry out CCTV survey to assess improvements and install pump on new Certalok uPVC rigid rising main
Borehole screens much cleaner.Water runs clear after borehole pumps being turned on, borehole now back in supply. Reduced running and maintenance costs due to more efficient borehole efficiency and cleaner water