In horizontal holes, several factors are affecting formation resistivity. The electromagnetic waves generated from the LWD tools are covering the adjacent beds and the reading can be highly affected. Moreover, when the well trajectory is cutting a bed boundary at a high angle, polarization horns are causing severe noise that masks the true formation resistivity. Recently, several wells in KOC had suffered the above mentioned effects causing great ambiguity in water saturation determination. Moreover, the use of LWD with natural radioactive sources has been always a big concern to KOC. An alternative option to resistivity was proposed to KOC based on using Sigma. The technique incorporates Pulsed Neutron Generators and acts as a multi-purpose measurement (Resistivity / Density / Neutron / Sigma / Spectroscopy). In addition, the technology can be used Sourceless. This technology was used for the first time in Kuwait with great success. The Sigma was used in the water saturation calculations. In addition, a time lapse Sigma was done where a second pass was recorded while pulling out of the hole. A comparison between drilling Sigma and reaming up Sigma was used to indicate any water movement by OBM invasion. Spectroscopy was also used for formation evaluation specially clay content. This is rather useful in complex lithology especially when the Gamma Ray reading is affected by strange mineralogy, thus affecting mobility calculations for accurate ICD design.

The 9 1/4-in. polycrystalline diamond compact (PDC) bit is a unique size necessary for long-interval deep-drilling casing programs in Kuwait. Drilling the section is a major challenge because the long interval consists of nonuniform lithology with variations in compressive strengths, and it contains an abrasive ultra-hard sandstone, a compact hard shale with a low rate of penetration (ROP) performance, and carbonates with shale, oolite, and sand traces. The interval is commonly drilled using either two or three new PDC bits, and extra trips are expected. Efforts were made to substitute the numerous PDC bit runs with one customized and reliable design that can overcome formation hardness and variations in compressive strength and maintain the same ROP to total depth (TD) with limited success, even though the idea of backup cutters has existed for decades. A new, durable PDC design was implemented with the objective of helping improve the ROPs across all intervals. The innovative backup cutter placement design and minimal critical depth of cut for each primary and backup cutter in the same radial position are the most desirable solutions. The new and innovative PDC cutters’ distribution structure using the new bit design software coupled with an innovative backup cutter placement minimized the calculated bit wear and maintained the cutters’ sharpness along the entire section without needing an extra trip or a new second bit, which produced the best performance achieved in the northwestern Kuwait fields. The new bit design achieved the longest footage drilled in Kuwait for a single bit of 9 1/4-in. size with a competitive ROP compared to previous cases. The used bit came out of the well in excellent condition with minimal normal wear. A case study of an innovative PDC cutting structure layout using the new PDC bit design with efficient backup cutter placement, bit formation interaction modeled to help predict cutting structure wear, and advanced rock mechanics analysis are discussed. The new backup cutters’ layout procedure extended bit life without sacrificing ROP.

Striking a balance between aggressiveness and steerability has always been a challenge in engineering new bit designs. The purpose of this paper is to highlight the engineering steps and challenges faced with designing a more aggressive bit that will drill faster while improving directional control and limiting vibrations to suit the application.North Kuwait's 8.5Љ build up section's geology comprises of layered carbonates, shale and sandstone. The section is known to induce vibrations in conventional RSS BHAs and can be challenging for directional work.As a rule, less blades in a PDC bit makes a more aggressive bit that is therefore harder to steer with. Historically Kuwait's 8.5Љ sections are drilled with a 6 bladed bit design. While proving stable, such a medium-set bit design limits performance in these formations.The engineering process involved: