In order to further enhance field development in North-West China land, wells were designed to drill 500m short 2-Dimensional curve section with 6~7deg/30m DLS and 2000m length horizontal leg using RSS+LWD BHA. Schlumberger as the contractor, was required to complete curve section in one run through soft shale, and to land in abrasive reservoir sand at over 3000m TVD. Great challenges were mainly on Bit selections, for good balance between steerability and aggressiveness of upper curve section Bit; while achieving minimum 3deg/30m DLS and durability in abrasive sand of horizontal section Bit. Additionally, efficient hole cleaning and BHA stability also play key roles on successful delivery of the wells.

After pre-job SQ workshop with operators, hitting target point in curve and maintain BHA's steering capability in horizontal drilling would be the priority concern, to save runs and avoid NPT due to RSS tool steering failure similar to previous operations in offset wells. Working together with contractor Drilling Engineering team, and applying 4D (3-Dimension + Time) FEA Dynamic Analysis System, we were able to offer highly customized and integrated proposal package—including recommended Bit, BHA design and Parameter window, to overcome challenges and optimize drilling efficiency.

The 4D FEA Dynamic Analysis System is capable of simulating downhole drill string dynamic behaviors with high accuracy, including Bit/BHA axial & lateral vibrations, stick slip ratio and statistic bending moment/stress distribution along BHA. With unique cutter-rock interaction data from lab test, it offers a large lithology catalog for select specific rock type to be matched with target potential lithology, and also capable of interbedded or sublayer simulation.

4D FEA System has been used to determine Bit selection and parameter window in the pre-job proposal. Our pre-job recommendations were fully taken by operator for field operations. Required DLS has been successfully fulfilled in both curve and horizontal leg, as indicated in FEA analysis. In one well, the record-breaking ROP (>8.6m/hr.) and long footage drilled (500m) had achieved successful well delivery. Also good downhole drill string stability has assisted well TD with over 2000m horizontal section length, achieving longest horizontal legs in whole West China land.

In FEA assisted proposal planning, multiple cutting structures selection was performed at initial stage. Vibration and stick slip were compared among 12 approved Bits in 12 simulation projects, for better Bit dynamic stability would significantly improve RSS tool face control and steering capability. In each project, 15 SRPM+WOB combinations were calculated, at curve and horizontal section respectively, with different sandstone Confining Pressures. Three stable candidate Bits were selected from over 700 simulation cases. Then consecutive comparison of ROP and DLS capability had fine-tuned the Bit selection among three stable options that were derived from previous analysis, and along with recommended parameter window margin.

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