Drilling Hard and Abrasive Rock Efficiently, or Generating Quality Cuttings? You No Longer Have to Choose…

Abstract

The drilling of hard formations usually requires specific drilling systems to achieve an efficient rate of penetration. Due to the limited depth of cut, the solution often involves the use of high RPM drive systems such as turbines or high speed motors and a fixed cutter product is usually the drill bit of choice. With increasing well depth the roller cone option is normally avoided due to the low penetration rates and limited rotating hours obtainable with these drill bits. Roller cone use invariably leads to multiple trips and a significant increase in the time and cost of the drilling operation, especially for deeply buried reservoirs where hard rocks are generally encountered and bit diameter is reduced at TD. Unavoidably, in some applications roller cone bits continue to be used in order to obtain the quality cuttings necessary for the geologist to correctly assess the formation. This is typically the case when the reservoir interval is encountered and exact formation knowledge is critical. A new drilling solution has been developed to address this situation and is presented in this paper. The idea consists of a fixed cutter bit which leaves the center of the hole uncut. The lack of bit center leads to the creation of a core. This core is broken by the bit itself and ejected at the side through a specifically designed junk slot. The core is then carried to the surface along with the other cuttings. This process leads to very high quality cuttings for surface examination. The improvement is especially important where normal cuttings quality is poor due to the use of turbines or high speed motors together with impregnated diamond bits. Importantly, as the center part of the bit is uncut this new technology also provides a significant increase in the rate of penetration. In a fixed cutter bit the center is one of the most inefficient cutting areas as the rotational speed of the cutter is low to null. By removing the center, an increased ROP efficiency in the range of 15 to 25 percent can be obtained depending upon the bit diameter. The field tests that are presented in the paper show quantifiable improvements in terms of geological sample quality, cutting efficiency and drilling cost reduction.

Unit Experimental Study on Impact Crushing Rock of the Microcoring PDC Bit

“…In view of the above conditions, a mass of related research has been carried out, and a mechanical microcoring PDC bit [9,10] is put forward to push the broken core column outward depending on the mechanical force of the rock. Tercel Corporation has developed a microcoring bit which can form a coring groove instead of cutting teeth in the central area of the bit, which improves the ROP and effectively solves the problem of difficult coring [11,12]. e bit developed by TOTAL and Diamond Drilling Services Company can produce microcores, which can not only ensure high drilling efficiency in hard formation drilling but also obtain high-quality cuttings [13].…”

Breakthrough PDC Technology Used in Saudi Arabia Deep Gas Wells to Significantly Reduce Drilling Time

“…The cutters incorporated in hard rock drilling bits are usually high abrasion resistant PDC cutters that are created with a process known as leaching that removes metal from the diamond. The leaching process increases the thermal stability of the PDC cutter by increasing the temperature at which the diamond thermally degrades, which enables the cutter to be engaged in high friction environments (Desmette et al 2008). The deployment of this technology and use of the new concepts and bit designing tools made it possible to significantly reduce the drilling time and cost associated in drilling the intermediate section in the Saudi Arabia deep gas wells.…”