Drilling to the Extreme: The Micro-Coring Bit Concept

Abstract

The growing interest in deeply buried reservoirs increasingly leads operators into extreme drilling conditions characterized by high hydrostatic pressure (over 20.000 psi) and high temperatures (over 300 °F), combined with hard formations (high CCS-40,000+ psi). Drilling in such environments requires specific adaptations of well design and in equipment selection. Additionally, these wells present multiple issues in well control, drilling and completion operations, and make the entire operation technically more complex and financially more risky.Referencing the specific example of drilling operations, the great depths and increased formation compaction leads to very low rates of penetration (ROP) and considerably extended operation time. These low ROPs equate to low depth of cut, and as a direct consequence the typical size of the drilled cuttings recovered at the shakers is extremely low (0.020 to 0.20 mm). This makes the cuttings irrelevant for the purpose of geological identification of the formations. This situation occurs with both impregnated diamond and PDC drill bits in these applications at low ROPs. If the downhole conditions (HPHT) exceed the MWD or LWD specifications, accessing critical geological information will necessarily require a challenging coring job, dramatically increasing the operation time and thus the cost of the well.

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

“…Nowadays, there are many evaluation criteria for the rockbreaking mechanism because of different evaluation indexes that are referred to, so a targeted solution is required according to different rock-breaking mechanisms. Two frequently used evaluation criteria for the rock-breaking mechanism are introduced [6].…”

“…In order to verify the lithology, the corresponding tools, equipment, and drilling fluid properties must be cooperated to sample the rocks so as to determine the properties of the rocks in the formation and understand the mineral conditions of the formation [2,3,4,5]. Nevertheless, the debris generated during the drilling process of the conventional PDC bits is in the powder form and too small for formation identification; thus, different types of bits are required to meet the demand of full drilling and coring [6,7,8]. 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.…”

Application of Resonance Enhanced Drilling to coring

“…Additionally, in order to improve rate of penetration (ROP) in hard and abrasive formations, some new coring bits have been developed to include hybrid bit technology combining rock roller and PDC technology [33]. Deschamps et al [34] and Tian et al [35] presented a specific drill-bit design that generates micro-cores of formation during conventional drilling operations, which are returned to the surface with the drilling fluid and cuttings. Guarisco et al [36] designed a PDC core bit to minimize vibrations while coring and reduce the chance of core jamming.…”