The Jurassic reservoirs of deep wells in Kuwait have traditionally been drilled with OBM. Barite is utilized as the weighting material in the OBM resulting damages to these reservoirs, thereby reducing the productivity to a significant extent. The higher oil to water ratio (95/5) of OBM limits the possibilities of identifying the micro fractures in reservoirs due to the limited conductive medium in OBM. Potassium formate WBM, with Manganese Tetraoxide as weighting material was successfully applied in HPHT wells overcoming these limitations. K-Formate brine was utilized up to maximum density of 12.5 ppg to reduce the impacts of solids in the mud. For the first time, maximum mud weight of 17.8 ppg was achieved operationally using micromax (Mn3O4) in this WBM. Also, for the first time in Kuwait, this kind of fluid was used to drill the section with the inclinations above 60° in deep wells. As a result of using K-Formate WBM in the reservoir sections, production increased significantly when compared to the wells drilled with OBM and barite. Wells were simulated easily without the presence of barite. Water based conductive medium gave better quality of image logs. Unlike other WBM's, K-formate WBM was stored for long periods, over a year in the mud plants without any damage to the mud properties. Recycling reduced the overall fluid costs in the subsequent wells drilled with K-formate WBM. Environmental damage due to the OBM spills and cuttings were completely avoided; K-formate WBM is highly bio-degradable under atmospheric conditions and is environmentally friendly. The experience and success gained with its use on the initial wells led to the planned usage of this WBM on all deep exploratory wells. This paper explains the experiences gained and the achievements made over the years with K-formate WBM used for drilling the deep HPHT wells.

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Efficiently drilling the abrasive Zubair sandstone is one of the Middle East's most daunting challenges. Adding to application complexity, the pyritic formation is also interbedded with hard shale streaks and has a compressive strength that ranges between 3-10kpsi. In Kuwait, the formation is first encountered at a depth of approximately 9000ft and been drilled with mixed performance results based on bit diameter. Generally, the large diameter PDC bits are still struggling to achieve the durability objective with some wells requiring more than two PDCs to complete the short 1400ft hole section. In the smaller hole sections, technological advances have overcome the cutter/bit durability issue but with no significant improvement in ROP. The objective of an intensive bit optimization effort has focused on increasing penetration rates while striving to improve overall bit life/cutter durability. To accomplish the operator driven objectives without time-consuming field trails, the drilling team used a software system to calibrate rock strength. This data was used in conjunction with an advanced FEA-based modeling system to analyze different PDC cutting structures to select a PDC bit with the blade count and shearing configuration that would produce dynamically stable drilling. The bit body would be equipped with a new O2 cutter to increase abrasion resistance and maintain temperature at the cutter tip by using: 1) enhanced HTHP sintering process; 2) refined post-pressing process to improve thermal stability 3) optimized hydraulics to maximizing cutter cooling.

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