Location: Onshore, Australia
Job type : Vertical drilling
Formation : Intermittent coal and sandstone sections
Fluid type : Water based mud, 9.3ppg

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The Challenge

This field is particularly known for its notorious coal seam sections layered between stringers of high compressive strength sandstone. Some of these coal seams are continuous intervals up to 200ft long. This lithology combination is ideal for creating ledges and downhole hazards for drilling and wireline equipment to get suspended or stuck. One particular coal section had never had wireline logs below it. FRACSEAL (fine) identified as a physical mud additive, has the ability to deform into microcleats which can then stop further mud pressure transmission into the coal.

The Action

The operator used a basic KCl/Polymer fluid and as the coal seams approached the active system was pre-treated with 6 ppb of FRACSEAL (Fine). Concentrations of 7-8ppb were added in subsequent premix treatments. Drilling 81/2” hole through this interval no obvious signs of hole instability occurred. Shakers were dressed with 110 mesh screens and the centrifuge was run as per normal. Both these pieces of SCE were monitored for stripping. Several coal intervals were passed with no signs of wellbore instability. Normal drill pipe pressures and pump rates were maintained.

The Result

TD was reached without any NPT and the hole was successfully logged to depths never previously reached. Post well analysis indicated that well trajectory within the field structure was on a “typical case” stress zone. FRACSEAL (fine) was successfully applied in this case and was integral to achieving the wellbore objectives. A secondary benefit in this case was reduced differential sticking in the intermittent sandstone sections.