Maintaining cutter integrity through a highly abrasive horizon

The onshore Oshskoye Field is in the Timan-Pechora region of northwestern Russia and is characterized by a complex geology. In terms of rock failure, the field's most complex interval is the Starooskolsky horizon of the Devonian system. The horizon is up to 558-ft [170-m] thick and consists of highly abrasive, strongly cemented quarzitic sandstones. These rock properties can considerably reduce the life of bits of any type or classification.

Previously, LUKOIL-Komi drilled wells with five sections requiring liner completions in the Starooskolsky horizon. The liner interval was drilled with diamond-impregnated 6 1/8-in [155.6-mm] bits in combination with either turbodrill systems or high-speed downhole motors. The average footage was 574 ft [175 m] at an average ROP of 4.6 ft/h [1.4 m/h]. This well construction strategy in the high-abrasion sandstones often resulted in cutting structure wear across the bit gauge and gauge loss.

When LUKOIL-Komi decided to shift from five sections per well to four sections, the 6⅛-in bit was eliminated and the aim was to drill the Starooskolsky horizon with 8 5/8-in [219.1-mm] bits. With this move, LUKOIL-Komi sought a PDC bit design that would tolerate abrasion in the field and maintain the same or better ROP and durability as diamond-impregnated bits, while drilling the section without unnecessary trips.

Drilling with unique cutting structure for maximum ROP and minimal trips

Schlumberger drillbit engineers suggested using the 8 5/8-in [219.1-mm] Z813 StingBlade bit with uniquely shaped Stinger elements combined with a PowerPak motor. StingBlade bits have been shown to enable operators to achieve increased footage and ROP with improved durability and impact strength as well as low vibration levels.

The engineering service within the LUKOIL-Komi drilling department worked with directional drilling engineers from Schlumberger to implement the integrated approach. Together the teams developed a directional drilling program to reduce well construction time in S-type wells through the use of StingBlade bits in the Oshskoye Field.

Boosted ROP 70% over wells drilled previously in the same formation

The first well drilled with the new bit and drilling program (Well 723) was on Pad 734 of the Oshskoye Field. For the first time in the history of the field, the highly abrasive Starooskolsky horizon was drilled with a PDC bit in one run using the StingBlade bit. LUKOIL-Komi drilled the entire 8 5/8-in [219.1-mm] section at a record-high ROP of 36.8 ft/h [11.2 m/h] in two runs using two bits.

In Well 723, average ROP increased 70% compared with other drilled wells. Construction time of the section was reduced by 9.2 days and 1.1 days compared with the best well drilled previously with diamond-impregnated bits from a third-party oilfield services provider.