Multiple deep geothermal wells up to 3,000m TVD/4,100m MD with BHT of 100°C were drilled to provide green energy to city districts within Europe. The first two wells (Well 1 & Well 2) were both drilled with a standard Potassium Carbonate/Xanthan/PAC based drilling fluid and both wells encountered several drilling and fluid related issues. To overcome these issues a Pure-Bore® based system was introduced for the drilling of Well 3.
Drilling through the Quartiär formations comprising of interbedded sandstone, young and highly reactive clay and chalk formations, made this a technically challenging project. The Jura formation comprised of fractured sandstones and into the target Malm (Jurassic) formation. High levels of clay dispersion, excessive rheology, foaming, excessive solids loading, bit balling issues, low ROP, high dilution, disposal volumes and a stuck pipe event on one well, led the operator to look at alternative drilling fluid solutions to deliver a technically more effective and cost efficient
Given the issues experienced on the first two wells, and considering that the use of chlorides are prohibited in this area, a Potassium Carbonate Pure-Bore® based fluid was proposed for Well 3, combined with the unique properties of the Pure-Bore® products to overcome all of the issues. The proposed Potassium Carbonate/Pure-Bore® system has several advantages such as a highly shear thinning rheology, no bit balling, improved ROP, significant shale encapsulation, improved solids control efficiency through finer shaker screens hence reduced dilution volumes. These features would eliminate the issues seen previously with the Potassium Carbonate/ Xanthan/PAC system facilitating good hole cleaning and minimised clay dispersion. Furthermore, the efficiency of the Pure- Bore® system aids in reduced low-gravity solids concentrations which reduces the dilution and disposal volumes delivering a very cost-effective project with less days required to complete the well.
Total Pure-Bore® based system cost savings of 31.9% compared to average of both Well 1 and Well 2.