Recent manufacturing and hardfacing advances have produced a steel-body PDC bit (SB-PDC) capable of efficiently drilling interbedded formations at significant depth. These technological advances have increased the bit's resistance to abrasion/erosion and enabled a new style steel-body PDC bit to drill formations in Egypt's western desert previously drilled by matrix PDC bits. Field tests have confirmed the steel-body PDC bit can outperform matrix PDCs in a wide-range of interbedded applications that contain a heterogeneous mixture of shale, sand/siltstone, and limestone. The approach combines optimized cutting structure design and premium PDC cutters that enable the steel-body PDC bit to drill the abrasive sand/siltstone component. The bit can also efficiently drill shale and soft limestone due to its hydraulic efficiency which was a factor limiting performance improvement in previous designs. The bit solution employs: ➣Cutting structure optimized using FEA-based modeling system➣Premium grade PDC cutters➣Next generation of abrasion/erosion resistant hardfacing material➣Hydraulically efficient bullet-shaped body type The new SB-PDC technology was deployed in a sequence of tests in different applications and fields in Egypt's western desert. The trials were run in different lithologies at different depths. Direct comparisons to relevant matrix PDC technology and other available steel-body bits clearly demonstrates the new-style steel-body PDC bit's value by setting new benchmarks and reducing cost/ft.
Drilling the deep lithology column using PDC bits in the Obayied field of Egypt's Western Desert has been extremely difficult. The field's lithology column represents an amplification of all of the typical lithology characteristics in the Western Desert. The highly interbedded sandstone, siltstone, and shalealong with the variance of such interbedding across the field-has been a significant challenge for well planners and has adversely affected cost per foot. The application is characterized as predominantly abrasive and impact-intensive in the same section, hence challenging for PDC bit durability. To efficiently drill the 8½-in interval, a fundamental change in PDC bit design is required.Considering these formidable challenges, service providers had to evolve PDC bits to meet the constant demand of improving performance and reducing costs. Focus was concentrated on balancing new technology developments and the willingness to invest on field trials. To accomplish these objectives in the Obayied field, the operator and the service provider identified two main problems-developing an in-depth understanding of rock strength characteristics of each individual formation in the deep rock column and its variance across the field, and developing PDC bits that can survive such a challenging rock column with improved durability and ROP.Recently, a novel conical diamond element (CDE) with extreme impact-and abrasion-resistant characteristics has been developed. The CDE has been incorporated at bit center in a new and innovative PDC design, solving the traditional challenge of the inefficient characteristic of PDC bit central area. In addition, a field-wide rock strength study based on sonic and gamma rays logs provided the transparency required for better planning and risk management to resolve the operational inefficiencies traditionally seen in the Obayied field.The new PDC bits utilizing the CDE technology has been deployed in Obayied and has reduced consumption to just 3-4 bits per section in 2014, whereas that number was 8 -10 bits per section averaged in 2006. The new bit has also reduced the average number of days to drill the section from as low as 6 days to reach TD instead of 20 days. Performance gains were achieved both in ROP and footage totals in the most challenging formations, including Alam Al Buwaib, Upper Safa, and Lower Safa. The authors will discuss the benefits of this industry collaboration that achieved exceptional performance improvement leading to dramatic cost savings in the Obayied field.
Drilling the top hole section in Egypt's Western Desert has proven to be a challenge because finding the optimal balance of drilling speed, pulling out of hole without issue, and running the casing without clay swelling is critical. Historically, a standard milled-tooth (MT) bit, slick BHA, and top hole mud system were used for economic considerations. Recently, a problem arose when drilling a 17½-in surface hole in the Western Desert Moghra sand and Dabaa area, where the formation is composed of swelling clays that caused delays and cost increases.The solution to combat clay swelling would require an effective mud strategy; a PDC design that could increase ROP and resist balling while remaining economic; and a slick BHA that ensured hole verticality without the aid of directional tools and minimizes the affect of drillstring dynamics for prolonged PDC bit life. The intent of such optimization is providing enough buffer time for the casing to be run without problems, and the overall solution needs to be more economic than the previous drilling practice.An integrated BHA, bit design, and mud strategy were deployed in a field test with outstanding results. The results showed a step-change in ROP performance and allowed a trouble-free hole. The PDC bit and slick BHA successfully mitigated vibrations and maintained verticality. The application of customized drilling fluid formulation that contained high-performance shale stabilizers with the redesigned mudweight schedules and early fluid displacement resulted in significant enhancements in tripping while drilling as well as in running and cementing the 13 3 ⁄8-in casing.
One of the perceived drawbacks of matrix polycrystalline diamond compact (PDC) bits compared with steel PDC bits is their restricted open-face volume and smaller blade standoff, which is primarily caused by the matrix PDC bits' brittle nature. Increased blade standoff gives steel PDC bits a more hydraulically efficient body type, which directly affects ROP. In many drilling applications, operators switch to steel PDC to take advantage of their hydraulic efficiency, and recent developments in hardfacing material has expanded the range of applications of such bits. However, there are applications that are still dominated by matrix PDC bits, and a need arose for matrix material that can allow the molding of slim, hydraulically efficient matrix bodies. A new matrix material with enhanced toughness allows for the design of a slim-body matrix construction. This innovative concept has been validated for structural integrity, which was the main perceived risk. The technology was rolled out for 8½-in and 12¼-in hole sections and deployed in a field test campaign in all of Egypt's different rock columns. The effect and value of faster ROP increases with application complexity and depth and is directly proportional to rig spread rate. Hence, realizing the application limits of slim-body matrix technology was the main intent of this study. Success was measured by observing the effect of hydraulic efficiency across different fields in terms of ROP and cost savings. Further, to isolate the effect of slim-body construction, several tests were conducted between standard matrix and slim-body matrix construction using the same cutting structure layout and PDC cutter grade. The slim-body matrix construction demonstrates significant improvement in cost per foot for applications and is directly proportional to UCS. This feature is advantageous in interbedded applications, where formations fluctuate from hard to soft and vice versa along the drilled column. This new feature has since been standardized in matrix bits and is being rolled out across various applications with the intent of tackling more expensive drilling operations to show a greater reduction in cost per foot.
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