Unique Mud System Delivers Water Main Project

MI-SWACO recently partnered with Brisbane-based Customized Drilling Services to drill a challenging HDD (horizontal directional drilling) bore in White Patch, a small community on Bribie Island, Queensland, Australia.

Customized Drilling Services (CDS) specializes in trenchless HDD solutions and pipeline infrastructure installation methods and was engaged by the regional utility provider to install 283m of OD250 PN12.5 PE100 HDPE water main to replace the existing pipeline that had been damaged during severe storms.

The site location which was on the edge of the Bribie Island National Park and ran parallel to the shores of the Moreton bay Marine Park presented significant environmental and operational challenges. CDS Operations Manager Matt Lee said “It was critical that we considered the environmental impact of any drilling fluid we utilised on the job but at the same time we needed products that were going to perform well in a shoreline bore.”

The borehole intersected a tidal inlet with the formation consisting mainly of coarse grained sand and poorly cemented coffee rock at a maximum cover depth of 9.8m from the point of entry.

MI-SWACO carried out downhole hydraulics simulation using their Virtual Hydraulics software to establish the optimum pumps rates and rates of penetration (ROP) to achieve good hole cleaning whilst minimizing downhole pressures.

Once the operational parameters had been established, MI-SWACO worked closely with the team at CDS to develop a cost effective, salt water tolerant drilling fluid that would deliver the hole cleaning function and borehole stabilization required in the tricky ground conditions.

CDS utilised their Ditch Witch AT40 drilling rig to execute the 3 stage horizontal bore: Pilot 5.5” single pass, 10” ream – single pass and final 15” ream single pass. Pump rates were maintained at 189 L/min (50gpm) on the pilot and 227 L/min (60gpm) and 238 L/min (63gpm) on the 10" and 15" reams. No cleaning passes were required.

MI-SWACO HDD Drilling Fluid Engineer Andrew Bilton recommended the DRILPLEX Mixed Metal Oxide (MMO) system for the project because of its low environmental impact, exceptional hole cleaning performance at low pump rates and its potential to reduce whole mud losses and borehole erosion in poorly consolidated (sand) and fractured formations.?

The DRILPLEX additive is used in conjunction with MAX GEL, MI-SWACO’s premium sodium Wyoming bentonite to provide an extremely versatile mud system with some very unique properties.

Due to the highly thixotropic nature of the mud system, the fluid maintains a low viscosity in the borehole where the fluid is moving quickly (pumps on), and gels up when the fluid stops moving (pumps off). This provides significant benefit by suspending the cuttings immediately and preventing the build-up of a cuttings bed on the low side of the hole. Drilled cuttings building up on the low side of the hole can result in increased downhole pressures, borehole instability and frac out (whole mud losses to the formation or to the surface).?

In unconsolidated formations the mud migrates into the pores and fractures and away from the fluid flow in the borehole. Here the mud instantly reverts to a gelled state creating a hydraulic barrier and thereby reducing the depth of invasion and preventing frac out. The mud system’s 10 second and 10 minute gel strengths were measured at 18 and 22 lb/100ft2 respectively demonstrating high initial and non-progressive gels.

The electrostatic interaction between the MAXGEL bentonite platelets and the DRILPLEX additive provides a strong initial bond but requires only very low shear stresses applied to the static mud to break the gels.?These unique properties allow sizeable cuttings to be suspended when the pumps are off and minimal pump pressure required to restart circulation even when the borehole is left for extended periods.

The product pipe was successfully pulled with no noticeable drag observed indicating a clean hole. The project was executed on time and in budget with zero HSE and LTI incidents. CDS Managing Director Dennis Wilson said “Delivering high quality solutions for all of our project partners and stakeholders is key to our success and this project was yet another example of this.”

Selecting the correct type of drilling fluid for the specific ground conditions and understanding borehole hydraulics is critical to a successful drilling operation. MI-SWACO provides a complete fluid engineering service including downhole hydraulic simulation, fracture gradient analysis and drilling fluid laboratory testing.

A complete range of HDD specific drilling fluid additives are available across Australia and New Zealand through our distribution partner Blick Industrial.

Contact MI-SWACO to see how we can help guide the decision making and planning phases of your next project.