Bulletin of the Geological Society of Malaysia, Volume 81, May 2026, pp. 57 – 70
Hydrogeological challenges in drilling fractured hardrock aquifer in Kedah
Prakasini D.1,*, Vijayan V.R.1, Zamani A.S.3, Alvyn C.M.2
1 VGX Sdn Bhd, Megan Avenue II, Block B, Level 8, Unit 1, Jalan Yap Kwan Seng, 50450 Kuala Lumpur, Malaysia
2 JMG, Level 9, Menara PjH, No. 2, Jalan Tun Abdul Razak, 62100 Putrajaya, Malaysia
3 JMG, Jalan Perak, Seberang Jalan Putera, 05150 Alor Setar, Kedah, Malaysia
* Corresponding author email address: prakasini.vgx@gmail.com
Abstract: This paper presents and discusses the hydrogeological challenges encountered during the drilling of fractured hardrock aquifers in Kedah, Malaysia. The project aimed at drilling 20 boreholes, each to a target depth of 200 meters, across various geological formations. However, initial drilling efforts faced several challenges, including high downhole pressure, fractured zone collapse, insufficient compressor capacity, and unexpected geological conditions, which initially prevented the boreholes from reaching the target depth. Several improvements were introduced to overcome these challenges, including modifying the borehole diameter, adjusting drilling techniques, and installing temporary casing until fresh bedrock was encountered. The most significant improvement was reducing the borehole diameter. Initially, a 10-inch diameter borehole was required to be drilled to a full depth of 200 meters, but difficulties arose when using the DTH hammer beyond 100 meters, especially in hardrock sandstone formations combined with high downhole pressure. A telescopic approach was used, where the diameter was reduced from 10” to 8” to continue drilling. However, this approach proved ineffective due to the water pressure/flow rate decrease when discharge water transitioned from the 8” to the 10” diameter opening, which prevented effective flushing of the drill cuttings to the surface. Ultimately, it was decided to drill an 8” diameter borehole directly from a 10” temporary casing to a depth of 200 meters with no telescoping. This approach succeeded and allowed the team to reach the target depth in all subsequent boreholes, even in fractured formations. Another factor that aided in achieving the 200 meters target depth was improving drilling speed, particularly in poorly consolidated lithologies such as interbedded mudstone formations, to prevent borehole wall collapse. Effective drilling in these fractured formations requires skillful drillers, well-maintained equipment, and experienced hydrogeologists on site.
This paper highlights the importance of proper well design and development, emphasizing the need for appropriate techniques before PVC installation to optimise and sustain yield during pumping. Additionally, the use of downhole geophysical tools to capture subsurface conditions including the location of major fractures contributed to a more efficient well design process. With these adaptations and proper well development, the subsequent 10 boreholes were successfully drilled to the target depth of 200 meters, providing valuable insight into groundwater dynamics in Kedah’s fractured hardrock hydrogeology.
Keywords: Groundwater drilling, hardrock aquifer, drilling techniques, well development, hydrogeology, Kedah
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Manuscript received 3 January 2025;
Received in revised form 11 March 2025;
Accepted 30 April 2025
Available online 29 May 2026
https://doi.org/10.7186/bgsm81202606
0126-6187; 2637-109X / Published by the Geological Society of Malaysia.
© 2026 by the Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC-BY) License 4.0.
