The 16′ Vertical Performance Motor Section is the most challenging section in Exploration Deep Drilling in Burgan Field & All South East Kuwait. The section comprises drilling hard and abrasive Zubair formation followed by reactive Ratawi Shale formation. Several technologies were introduced during the last ten years in search of an economic solution to deliver this section safer and faster with limited success. The objective of this paper is to present the process and technology implemented to drill Zubair and Ratawi Shale formations in two different wells with the same bit at record rates of penetration. Bit durability is generally the main driver in the 16′ section performance. Historically, one to two polycrystalline diamond compact (PDC) bits were utilized in this section and were pulled out for low penetration rates. The new solution required a thorough offset data analysis, including formation porosity, rock strength and abrasiveness analysis, applied drilling parameters and Mechanical Specific Energy (MSE) analysis using software. A customized PDC bit design was then developed using a state of the art bit/formation interaction model combined with an advanced cutter technology and hydraulics pairing for ultimate cutter cooling. The new PDC bit design and the implementation of the softwares used to analyse offset wells drilling parameters and rock mechanics had a significant effect on the bit durability and Rate of Penetration (ROP). The optimized drilling parameters applied as per the former set roadmap aided in managing the bit cutting structure through Zubair and Ratawi Shale formations and the bit was pulled out in re-runnable condition with a new field ROP record. The same bit was then used again in different well and drilled Zubair and Ratawi Shale formations and pulled out with 1, 3 dull condition. Over the two wells drilled, the optimized drilling plan saved National Oil Company over US $200,000, reducing the cost per foot (CPF) drilled by 38% over the field average CPF, increasing the ROP by 55% over the field average and drilling 69% footage more than the previous section benchmark footage. With the engineering evaluation of the offset data and the utilization of the new bit design, National Oil Company managed to drill Zubair and Ratawi Shale section in two different wells with the same bit for the first time and was able to improve drilling efficiency and cutting the drilling cost by eliminating bit trips and cost of new PDC bits.
To drill deepening hole below 7" liner through deep section of compact interbedded carbonate formation results slow rate of penetration (ROP). Beside the limberness of BHA configuration (which is stiffer for the larger sizes of BHA) thus generates various string vibrations, the used of heavier mud weight can also effect overbalance pressure thus reduces drilling ROP. This paper outlines the two stages diameter PDC bit, that proficiently increases drilling efficiency in order to produce faster ROP through small hole, deep section drilling. When the PDC bits cutting structure is separated into two stages of hole diameters, the mechanical energy that is required to destroy a given volume of the rock to drill can be significantly reduced. This energy reduction can be equivalent to the percentage of the hole size reduction relative to the final hole diameter. The reduced hole diameter that is described as pilot hole will be drilled by the first stage of the bit. The second stage of the bit that is called as reamer section simply enlarges a stress relieved pilot hole, to a final hole diameter. The Mechanical Specific Energy (MSE) concept that is defined as work that is required to fail a given volume of rock has been formulated proportionally with formation rock strength. MSE can also be defined as input energy to result ROP. The ROP to drill a smaller hole is faster than ROP to drill larger hole although with similar BHA, whilst ROP to enlarge a pilot hole always faster than ROP to drill the pilot hole. Because the bi-center bit has a pilot section that can be used for drilling a smaller pilot hole and a reamer section for enlarging pilot hole to a final hole size, therefore it shoud be able to produce faster ROP compared to conventional one stage PDC bit. The field results revealed that all of 5–3/4" x 6–1/2" and 6" x 7" bi-center bits that were run below 7" casing by Kuwait Oil Company in Kuwait - through deep wells, have drilled the intervals more than 30% faster than conventional PDC bit. Introduction Kuwait Oil Company Deep Well Division have drilled several deepening hole below the 7" liner in order to produce hydrocarbon from the lower intervals of the existing production wells through several fields that were explored in 1950's decade. These deepening well drilling campaigns have been actively performed through the oil field located on the northern area of Kuwait that is shown on map, Figure-1.
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