Page 50: of Offshore Engineer Magazine (Sep/Oct 2014)

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Claudio Paschoa discusses Stinger

Drilling conical diamond technology with João Pedro Tocantins,

Senior Product

Engineer from

Schlumberger’s

Smith Bits.

Stinger technology aims to optimize pre-salt drillingto optimize pre-salt drilling mith Bits’ innovative Stinger to the center of the cutting structure; The CDE, centrally placed in a PDC drill bit cutting structure, increased ROP conical diamond element increases rock removal by the center-most cutters and stability.

Images courtesy of Smith Bits, a

S drilling speed and improves stabil- is much less ef? cient, especially in hard

Schlumberger company.

ity, showing good potential for tackling formations. Because the center cutters the complex pre-salt formations. This bear the highest load, operational and to conventional PDC cutters is preva-

Smith Bits technology is focused on rock formation changes can cause large varia- lent–For example: the pre-salt formation destruction ef? ciency to increase drill- tions in depth of cut (DOC), including bit offshore Brazil–and the main limiter for ing performance. The Stinger element torque ? uctuations. performance. is located at the bit’s center and enables This results in decreased drilling

OE: Are PDC bits still dominant in the high-point loading to fracture rock more ef? ciency at the center of the bit’s cut- drilling market?

ef? ciently for increased durability and ting structure, which can cause low rate of penetration (ROP). ROPs, destructive lateral vibrations, and Yes, with continuing advances in cutter damage. To decrease damage and synthetic diamond cutter technology

OE: Could you tell us what led to the increase performance at the center of a and improved bit stability, PDC bits development of the central Stinger?

PDC bit’s cutting structure, bit design have become the dominant force in the

A common challenge to conventional engineers conceived a center-placed coni- worldwide drilling scheme. In 2004,

PDC bits is that they are inef? cient at cal diamond element (CDE). total footage drilled by diamond bits removing rock from the center of the To position the element in the bit, engi- (54%) surpassed that of roller cone bits borehole, because the rotational velocity neers removed the center cutters. The (46%) and the trend has continued. Due of cutters decreases with their proximity absence of these cutters allows a stress- to its reliability the system Turbine + relieved column Impregnated bit have been used quite fre-

Cutter force and velocity plot for conventional of rock to develop quently in the pre-salt formation offshore 8.75-in, 6-blade PDC with 16-mm cutters while drilling, Brazil. 1 1 which continu-

Highest 0.9 0.9

OE: Has thermal damage when drill- ously fractures and load cutters 0.8 0.8 ing in highly abrasive formation been crushes, thereby decreased by using the PDC bits with improving drilling 0.7 0.7

Relative Relative cutter forcecutter force conical diamond Stinger element and ef? ciency. The 0.6 0.6 why is it less susceptible to this kind of

Stinger technology 0.5 0.5 damage?

is a new line of 0.4 0.4

Yes, this happens because the PDC bits

PDC drill bits that

Relative Relative 0.3 0.3 cutter velocitycutter velocity with conical diamond Stinger element incorporate the 0.2 0.2

Normalized cutter force fails the rock through crushing action. conical diamond

Normalized cutter velocity 0.1 0.1

The load is concentrated at a single elements called 0 0 0.5 11.522.53 3.5 4 4.5 5 0 point, which signi? cantly reduces the

Stingers in the required load to fracture the rock. The center of the bit.

Distance from bit center, in effect of this single-point loading is

This product was

This plot shows typical forces and cutter velocity, from bit center compounded with a Stinger element intended for appli- to the gauge. The center. Most cutters experience the highest because the column of rock that the cations where loads and have the lowest rotational velocity, subjecting them to more stress.

bit allows to develop is isolated and impact damage

September 2014 | OE oedigital.com 52 052_0914_D&C2_presalt bits.indd 52 8/21/14 4:15 PM