Stability Analysis of Pressure and Penetration Rate in Rotary Drilling System

The purpose of this paper is to stabilize the annular pressure profile throughout the wellbore continuously while drilling. A new nonlinear dynamical system is developed and a controller is designed to stabilize the annular pressure and achieve asymptotic tracking by applying feedback control of the main pumps. Hence, the paper studies the control design for the well known Managed Pressure Drilling system (MPD). MPD provides a closedloop drilling process in which pore pressure, formation fracture pressure, and bottomhole pressure are balanced and managed at the surface. Although, responses must provide a solution for critical downhole pressures to preserve drilling efficiency and safety. Our MPD scheme is elaborated in reference to a nontrivial backstepping control procedure and the effectiveness of the proposed control laws are shown by simulations.

Numerical Modeling of the Effects of Pore Characteristics on the Electric Breakdown of Rock for Plasma Pulse Geo Drilling

Drilling costs can be 80% of geothermal project investment, so decreasing these deep drilling costs substantially reduces overall project costs, contributing to less expensive geothermal electricity or heat generation. Plasma Pulse Geo Drilling (PPGD) is a contactless drilling technique that uses high-voltage pulses to fracture the rock without mechanical abrasion, which may reduce drilling costs by up to 90% of conventional mechanical rotary drilling costs. However, further development of PPGD requires a better understanding of the underlying fundamental physics, specifically the dielectric breakdown of rocks with pore fluids subjected to high-voltage pulses. This paper presents a numerical model to investigate the effects of the pore characteristics (i.e., pore fluid, shape, size, and pressure) on the occurrence of the local electric breakdown (i.e., plasma formation in the pore fluid) inside the granite pores and thus on PPGD efficiency. Investigated are: (i) two pore fluids, consisting of air (gas) or liquid water; (ii) three pore shapes, i.e., ellipses, circles, and squares; (iii) pore sizes ranging from 10 to 150 μm; (iv) pore pressures ranging from 0.1 to 2.5 MPa. The study shows how the investigated pore characteristics affect the local electric breakdown and, consequently, the PPGD process.

Drilling Automation: The Step Forward for Improving Safety, Consistency, and Performance in Onshore Gas Drilling

In the current oil and gas drilling industry, the modernization of rig fleets has been shifting toward high mobility, artificial intelligence, and computerized systems. Part of this shift includes a move toward automation. This paper summarizes the successful application of a fully automated workflow to drill a stand, from slips out to slips back in, in a complex drilling environment in onshore gas. Repeatable processes with adherence to plans and operating practices are a key requirement in the implementation of drilling procedures and vital for optimizing operations in a systematic way. A drilling automation solution has been deployed in two rigs enabling the automation of both pre-connection and post-connection activities as well as rotary drilling of an interval equivalent to a typical drillpipe stand (approximately 90 ft) while optimizing the rate of penetration (ROP) and managing drilling dysfunctionalities, such as stick-slip and drillstring vibrations in a consistent manner. So far, a total of nine wells have been drilled using this solution. The automation system is configured with the outputs of the drilling program, including the drilling parameters roadmap, bottomhole assembly tools, and subsurface constraints. Before drilling every stand, the driller is presented with the planned configuration and can adjust settings whenever necessary. Once a goal is specified, the system directs the rig control system to command the surface equipment (draw works, auto-driller, top drive, and pumps). Everything is undertaken in the context of a workflow that reflects standard operating procedures. This solution runs with minimal intervention from the driller and each workflow contextual information is continuously displayed to the driller thereby giving him the best capacity to monitor and supervise the operational sequence. If drilling conditions change, the system will respond by automatically changing the sequence of activities to execute mitigation procedures and achieve the desired goal. At all times, the driller has the option to override the automation system and assume control by a simple touch on the rig controls. Prior to deployment, key performance indicators (KPI), including automated rig state-based measures, were selected. These KPIs are then monitored while drilling each well with the automation system to compare performance with a pre-deployment baseline. The solution was used to drill almost 60,000 ft of hole section with the system in control, and the results showed a 20% improvement in ROP with increased adherence to pre-connection and post-connection operations. Additionally, many lessons were learned from the use and observation of the automation workflow that was used to drive continuous improvement in efficiency and performance over the course of the project. This deployment was the first in the region and the system is part of a comprehensive digital well construction solution that is continuously enriched with new capabilities. This adaptive automated drilling solution delivered a step change in performance, safety, and consistency in the drilling operations.

Novel Motor Adjusts Bend Setting Downhole, Addressing Today's Directional Drilling Challenges

Previously, few options existed for the complex directional challenges. Drillers either needed to rely on multiple Bottom Hole Assemblies (BHAs) or use expensive drive systems, which resulted in increased operational cost and limited drilling flexibility. This novel Downhole Adjustable Motor (hereafter referred to as downhole adjustable motor or the motor) described in the paper addresses these limitations by enabling the driller to change the motor bend in real-time downhole. In addition, the motor can deliver up to 1,000 horsepower (HP) at the bit during rotary drilling—the highest power in its size range. This paper will review how, even in harsh drilling applications, the downhole adjustable motor has proven to save trips, increase bit life, reduce lateral vibrations and stick-slip, and allow for drilling optimization to increase Rate of Penetration (ROP) and decrease overall drill time. Whether for drilling contracts or lump-sum turnkey projects, the directional drilling industry benefits from this new technology's ability to improve drilling economics while increasing safety by reducing drillpipe tripping and additional BHA handling.

Is Titanium Drillpipe Applicable to Offshore Drilling? A Question from a Corrosion Fatigue Perspective

Summary In offshore horizontal well drilling, one of the major challenges is the large dogleg severity in the buildup section due to the shallow depth of reservoirs. In such a case, the drillstring has to bend itself to fit the borehole trajectory and suffers greatly from the high alternating stress while rotary drilling. This could lead to fatigue fracture of the drillpipe within a short period. The corrosion from drilling mud may exacerbate the failure risk. Titanium alloy, as a new drillpipe material, has the characteristics of excellent corrosion resistance and low elastic modulus, which can theoretically extend the fatigue life. To study the performance of titanium alloy drillpipe quantitatively, titanium alloy material, and G105 steel of the same grade are compared to obtain the microscopic characteristics and macroscopic properties through experimental tests. Moreover, the mechanism of passive film formation of the two materials is analyzed in the corrosion fatigue (CF) environment. Then, the experimental results are extended to modeling the actual drillstring assembly and simulating its service life in the field practice of offshore drilling. Our numerical results indicated that the titanium alloy drillpipe has much better corrosion resistance but only half the stress level of G105 steel under the same dogleg severity and axial force, which makes its fatigue life over 23 times longer. Eventually an economic appraisal is given by considering the full-service life of the drillpipe. The research results of this paper can provide a detailed theoretical basis and reference for field application and can popularize the use of titanium alloy drillpipe.