Investigation on Axial-Lateral-Torsion Nonlinear Coupling Vibration Model of Drilling String in Ultra-HPHT Curved Wells

In view of the vibration failure of drilling string system in ultra-high temperature and high pressure (ultra-HPHT) curved wells, an axial-lateral-torsion coupling (ALTC) nonlinear vibration model of drilling string system was established using energy method and Hamiltonian principle, in which, the influence of wellbore trajectory change, wellbore constraint, interaction between bit and rock and ultra-HPHT of wellbore on elastic modulus and viscosity of drilling fluid were taken into account. The finite element method (FEM) is used to realize the numerical solution of the nonlinear vibration model. The correctness and validity of the ALTC nonlinear vibration model was verified by comparing the measured data of four ultra-HPHT wells with the theoretical calculation results of the proposed model. The research results provide a theoretically sound guidance for designing and practically sound approach for effectively improving rate of penetration (ROP) and the service life of drilling string in ultra-HPHT curved wells.

Analysis of initiation of instability zones of drilling string and intensification of drilling process at well boring by rotating an d rotating-bit methods

Instable operation of a drilling string can be caused by design flaws, unreasonably selected drilling modes, as well as specific features of the drilling by bit, fixed on a long flexible rod with initial irregularities. It was established that a drilling string under the influence of constant torque and longitudinal feed load is deformed along a screw line. It was shown that the source of the dynamic state initiation of a rotating drilling string is an alternative friction between rock and the instrument, as well as variation of potential energy of the drilling string at its twisting and untwisting. At the string twisting the potential anergy is accumulating, at the untwisting it is released. In this case the drilling sting length begins to increase and the work of feed force is imposed to this shifting resulting in the instrument beat over the rock. The torsion oscillating process causes longitudinal periodic shifting of the string end, which lead to joint longitudinal and bending oscillations of the whole drilling column. Systems of differential equations obtained describing the joint bending-longitudinal oscillations of a drilling string, caused by torsion vibrations, initiating at the contact of a drilling instrument with rock. Approximate solutions of the systems presented, which take place with the basic natural frequency of the torsion oscillations of a two-mass system instrument - string - rotator drive. In this case the amplitudes of the drilling string bending oscillations are associated with characteristics variation of the friction between the instrument and the rock as well as with the angular frequency of the drilling string rotation. Zones of dynamic instability at rotation of the deformed drilling string due to acting force factors, as well as initial irregularities and centrifugal forces revealed. It was shown that they are initiated at critical speeds of the drilling string rotation, which coincides with any natural frequency of the bending oscillations of the stave. To intensify the drilling process, recommendation elaborated for equipping the rotary drilling rig with an additional pneumatic hammer. A calculated diagram of a drilling string, equipped by an additional pneumatic hammer considered. Parameters of the hammer in terms of frequency and amplitude are matched with the translational speed of well drilling. The total longitudinal and transverse shifts can be obtained by superposition of self-exciting and induces shifts.

Efficiency of releasing stuck drilling string

While drilling oil and gas wells, 10–15 % of open part of wellbore consists of permeable fractured reservoirs and horizons. Despite of it, 70–80 % of failures occurring in wellbore fall on the permeable suites. After sticking electrical measurement only upper interval is specified. Then an oil patch is practically installed in abnormally complicated reservoirs in the upper permeable stuck and bottomhole intervals to prevent the complications and blowout. The drilling string often remains stuck beneath the upper suite in three-four suites to the bottomhole. It is necessary to install stepped oil bath to prevent it.

Evaluation of the conditions of drill pipes failure during tripping operations

The experimental evaluation of the power criterion for the metal fracture of the reserve and the long operated drill pipes was carried out. The conditions under which, during tripping operations, the failure of explored drill pipes, containing external or internal transverse annular cracks are possible. An interrelation between the depth of critical external or internal transverse annular cracks in drill pipes with the weight of the drilling string is considered, taking into account the influence of dynamic loads during tripping operations. It is shown that internal transverse annular cracks in lowering operating drilling strings at depths of more than 1400 m are more dangerous than external ones, while at depths up to 1400 m, external cross-sectional circular cracks are more dangerous.

Modeling research on the extreme hydraulic extension length of horizontal well: impact of formation properties, drilling bit and cutting parameters

Horizontal well can increase well productivity and improve the economic benefit, which significantly promotes the development of shale gas, tight oil and heavy oil. Moreover, it plays an important role in the development of natural gas hydrate. Horizontal extension ability is one of the key indexes of horizontal well, but it is always impacted by formation properties and well structure. Therefore, a model is established to analyze the impact of formation properties and well structure as comprehensive as possible, which considers not only traditional influencing factors, like formation pressure and drilling bit parameters, but also other key factors, including cutting particle size, wellbore diameter and cross section. Based on the analysis, some advises are proposed for field application. The analysis indicates that horizontal well has stronger extension ability in the formation with low formation pressure and high fracture pressure, but it is still limited by pump pressure. Under-balanced drilling can strength the extension ability in high formation pressure by reducing drilling mud density. The natural fractures in formation should be noted when drilling long horizontal well. The extension length increases and then decreases with the cutting particle size, so cutting particle has optimal size for the horizontal extension length, which can be adjusted by the rate of penetration and rotation speed. The extension length increases first and then decreases with the gap between drilling string and hole. Considering the demand of rock breaking and cutting sweeping around drilling bit, it is not recommended to adjust the drilling bit parameters. Both the cutting bed height and drilling string eccentricity have impact on horizontal extension length by changing minimum cutting-carry pump rate and annular pressure drop. Under different combinations of above two parameters, minimum cutting-carry pump rate and horizontal extension length are determined by different factors and can be divided into three parts, including acceptable cutting bed height, cutting lifting efficiency, pump pressure and total circulation pressure loss and well bottom pressure and formation fracture pressure. The findings of this study can help for better understanding of horizontal well hydraulic extension length and optimization method.

Environmentally-efficient approaches to oil and gas producing sites

We have offered the investigations aimed at the design of eco-efficient technologies during oil and gas producing sites life cycle. The authors have conducted the analysis of conditions causing environmentally hazardous situations at oil and gas producing sites. We have established the necessity of quick maintenance of operation during emergencies that makes it possible to reduce material costs and environmental pollution. The increase of environmental safety in the process of winding up oil and gas wells emergencies that took place as a result of catching drilling string or some other pipe is crucial. We have analyzed different ways and various structural designs of the devices for pipe unscrewing from caught strings. We have established the ways of negative environmental impact reduction in the winding up emergencies at operating as well at stack oil and gas rigs. The recommendations regarding the structural design of the device are given. The device design is patented and the prototype model of the device is designed and manufactured. The device functions as the transformer of clockwise drilling string rotation into anticlockwise rotation of fishing tools. We have highlighted the positive effects after the implementation of the given device. We have noted the importance of innovative technologies design as well as the importance of forming adequate response skills during emergencies when wellsites are being constructed. The technical solutions and recommendations we have introduced make it possible to prevent negative environmental impact and reduce resource flows at different stages of wellsite life cycle.

Methodology for determining the parameters of drilling mode for directional straight sections of well using screw downhole motors

Article presents results of study on possibility of increasing the efficiency of drilling directional straight sections of wells using screw downhole motors (SDM) with a combined method of drilling with rotation of drilling string (DS). Goal is to ensure steady-state operation of SDM with simultaneous rotation of DS by reducing the amplitude of oscillations with adjusting the parameters of drilling mode on the basis of mathematical modeling for SDM – DS system.Results of experimental study on determination of extrema distribution of lateral and axial oscillations of SDM frame depending on geometrical parameters of gerotor mechanism and modes ensuring stable operation are presented.Approaches to development of a mathematical model and methodology are conceptually outlined that allow determining the range of self-oscillations for SDM – DS system and boundaries of rotational and translational wave perturbations for a heterogeneous rod with an installed SDM at drilling directional straight sections of well. This mathematical model of SDM – DS system's dynamics makes it possible to predict optimal parameters of directional drilling mode that ensure stable operation of borehole assembly.