Enhancing Drilling Response and Improving ROP on PDC Bits by Utilizing 1-in. Diameter Cutters

This paper details the improvements to drilling performance and torsional response of fixed cutter bits when changing from a conventional 19-mm cutter diameter configuration to 25-mm cutter diameters for similar blade counts in two different hole sizes. Key performance metrics include rate of penetration (ROP), rerun-ability, torsional response, and ability to maintain tool-face control during directional drilling. A high-performance drilling application was selected with several existing offset wells using a 12¼-in., five-bladed, 19-mm (519) drill bit design, and a concept bit developed using 25-mm diameter cutters while maintaining comparable ancillary features. This was tested in the same field on both vertical and S-shape sections using the same bent-housing motor assembly and drilling performance compared to the existing offsets. A 17½-in. hole size application that experiences high drillstring vibration was also selected, and a 25-mm cutter diameter drill bit was designed with comparable ancillary features to replace a six-bladed, 19-mm (619) drill bit. This was tested in the same field with the drilling performance, and vibration propensity was assessed. Initial testing in the 12¼-in. section showed extremely promising initial results, breaking the field ROP record in a well-established field of more than 3,000 wells. The rerun of the same bit without repair placed fourth in the field in terms of ROP records. Additional testing in the vertical and s-shape sections showed the new 25-mm cutter diameter design consistently exceeding the ROP performance of the 519 drill bit design while achieving directional targets without any reported drilling concerns. Subsequent trials with other operators saw similar performance improvement with multiple instances of breaking field ROP records. The first trial of the new 17½-in. hole size design with 25-mm diameter cutters had 34% average higher ROP than the offset average ROP, achieving the field ROP record. An overall 70% improvement during trials was seen in ROP versus the existing 619 drill bit design. The daily drilling reports and client feedback reported a significantly reduced level of drillstring vibration versus offset wells. This paper demonstrates the potential for a paradigm shift in drilling response and overall ROP by using 25-mm diameter cutters on fixed cutter bits. When correctly modeled, designed, and selected for specific applications, they benefit operators by reducing the time it takes to drill the section, improving repairability, reducing the time that an openhole is left exposed, and reducing drilling costs.

Torsional Crack Localization in Palm Oil Clinker Concrete Using Acoustic Emission Method

Palm oil clinker (POC) aggregates is a viable alternative to the naturally occurring sand and gravel in the manufacturing of concrete. The usage of POC aggregates assists in the reduction of solid waste and preserves the consumption of natural resources. Although researchers investigated the mechanical response of POC-containing concrete, limited research is available for its torsional behavior. In general, the torsional strength depends on the tensile strength of concrete. This research investigates the compressive, tensile, and torsional response of concrete with various ratios of POC-aggregates. Five batches of concrete were casted with POC-aggregate replacing granite at ratios of 0, 20, 40, 60, and 100%. The selection for the mixture proportions for the various batches was based on the design of experiments (DOE) methodology. The hard density, compressive strength, splitting tensile strength, and flexural strength of concrete with a 100% replacement of granite with POC-aggregates reduced by 8.80, 37.25, 30.94, and 14.31%, respectively. Furthermore, a reduction in initial and ultimate torque was observed. While cracks increased with the increase in POC-aggregates. Finally, the cracking of concrete subjected to torsional loads was monitored and characterized by acoustic emissions (AE). The results illustrate a sudden rise in AE activities during the initiation of cracks and as the ultimate cracks were developed. This was accompanied by a sudden drop in the torque/twist curve.

A New Generation of Steerable Drilling Motor is Born - Understand the Unique Geometry, Drilling Benefits and Performance Gains

Steerable drilling motors still dominate US shale drilling applications. Shale well construction is commonly planned with monobore vertical, high dogleg-severity (DLS) curve and lateral sections. Limitations arise in each portion of the wellbore because one single bottomhole assembly (BHA) does not provide optimal results; hence, trips are required to optimize the BHA. The main disadvantage with existing steerable drilling motors is the requirement for high bend-angle settings to drill the high DLS curve portion of the wellbore. The geometry of a high bend-angle motor is only optimal for slide drilling the curve, it is not optimal for drilling the vertical and lateral portions of the wellbore. While drilling the vertical and lateral portions of the well, surface RPM (revolutions per minute) must be limited to reduce the cyclic bending fatigue on the large external bend. Not to mention poor wellbore quality while rotary drilling with a large external bend. To overcome this issue, a new geometry design was required. The new-generation motor uses a tilted internal drive mandrel aligned with a small external bend. This combination delivers the best of both worlds, providing high DLS capability while slide drilling and high surface-RPM capability while rotary drilling (because of the small external bend). Compact embedded drilling dynamics data recorders were used to validate the dynamic improvement of the new steerable-drilling-motor geometry versus older-style geometry with large external bend. The embedded sensors recorded at-point dynamics of shock and torsional response providing detailed comparative data sets during the development phase. The new-generation steerable-drilling-motor technology utilizes point-the-bit rotary-steerable-system (RSS) methods (for example, a tilted mandrel) with conventional steerable-motor methods (for example, an external bend). The combination of the internal tilt and external bend (aligned together) provides a completely new geometry for a steerable motor. This new geometry is beneficial for high DLS sliding capability, high surface-RPM rotary drilling and improved borehole quality (slide/rotate transition and rotary mode). This new steerable drilling motor with enhanced geometry was utilized to prove delivery of vertical/curve/lateral in one run, consistent DLS through the curve and improved tracking in the lateral. The results from development testing (comparing to older-geometry motors) will be described in this paper.

Evaluating the response of a modified Gent-Thomas strain energy function having limiting chain extensibility condition in torsion and azimuthal shear

The purpose of this paper is to investigate the torsion and azimuthal shear of an incompressible hyperelastic cylinder having a modified Gent-Thomas strain energy with limiting chain extensibility condition. First, the torsional response of the modified Gent-Thomas model is obtained analytically and compared with those of Gent-Gent, Gent-Thomas, and Carroll strain energy models where the former model incorporates the limiting chain extensibility condition while the latter two are phenomenological models. The results show the modified Gent-Thomas model to be in better agreement with the experimental data of Rivlin and Saunders on torsion than the other three models. To further evaluate the response of the modified Gent-Thomas model, azimuthal shear deformation of an incompressible hyperelastic cylinder with the modified Gent-Thomas, Gent-Thomas, Gent-Gent, and Carroll strain energies is considered, where the angular displacement in azimuthal shear is determined analytically for the first three models and numerically for the fourth model. It is shown that the strain hardening effect, predicted either by the limiting chain extensibility condition for the modified Gent-Thomas and Gent-Gent models or phenomenologically by the Carroll model, is quite significant in the azimuthal shear response of the incompressible cylinder.

Evaluation of Smeared Constitutive Laws for Tensile Concrete to Predict the Cracking of RC Beams under Torsion with Smeared Truss Model

In this study, the generalized softened variable angle truss-model (GSVATM) is used to predict the response of reinforced concrete (RC) beams under torsion at the early loading stages, namely the transition from the uncracked to the cracked stage. Being a 3-dimensional smeared truss model, the GSVATM must incorporate smeared constitutive laws for the materials, namely for the tensile concrete. Different smeared constitutive laws for tensile concrete can be found in the literature, which could lead to different predictions for the torsional response of RC beams at the earlier stages. Hence, the GSVATM is used to check several smeared constitutive laws for tensile concrete proposed in previous studies. The studied parameters are the cracking torque and the corresponding twist. The predictions of these parameters from the GSVATM are compared with the experimental results from several reported tests on RC beams under torsion. From the obtained results and the performed comparative analyses, one of the checked smeared constitutive laws for tensile concrete was found to lead to good predictions for the cracking torque of the RC beams regardless of the cross-section type (plain or hollow). Such a result could be useful to help with choosing the best constitutive laws to be incorporated into the smeared truss models to predict the response of RC beams under torsion.

DNA supercoiling-mediated collective behavior of co-transcribing RNA polymerases

Multiple RNA polymerases (RNAPs) transcribing a gene have been known to exhibit collective group behavior, causing the transcription elongation rate to increase with the rate of transcription initiation. Such behavior has long been believed to be driven by a physical interaction or "push" between closely spaced RNAPs. However, recent studies have posited that RNAPs separated by longer distances may cooperate via the DNA segment under transcription. Here, we present a theoretical model incorporating the mechanical coupling between RNAP translocation and the torsional response of supercoiled DNA. Using stochastic simulations, we demonstrate long-range cooperation between co-transcribing RNAPs mediated by DNA supercoiling. We find that inhibiting transcription initiation can slow down the already recruited RNAPs, in agreement with recent experimental observations, and predict that the average transcription elongation rate varies non-monotonically with the rate of transcription initiation. We further show that while RNAPs transcribing neighboring genes oriented in tandem can cooperate, those transcribing genes in divergent or convergent orientations can act antagonistically, and that such behavior holds over a large range of intergenic separations. Our model makes testable predictions, revealing how the mechanical interplay between RNAPs and the DNA they transcribe can govern a key cellular process.