The mechanical responses in monopole acoustic LWD and their relation with the output voltage waveform

Acoustic logging while drilling (LWD), characterised by simultaneous drilling and logging, is widely used to obtain the elastic parameters of the formation around the borehole. Most published monopole acoustic LWD simulation waveforms are routinely presented as pressure. However, these pressure waveforms disagree with the voltage waveforms recorded in the experiments. Here, to find out the reason of the inconsistent of these two waveforms, both the piezoelectric effect of the transducer and the propagation of the acoustic wave are integrally calculated with the finite-element method, obtaining the voltage waveform as well as the mechanical waveforms. The quantitative comparisons between the mechanical waveforms and the voltage waveform show that the output voltage cannot represent the pressure signal, but a combination of multiple mechanical signals. Based on the piezoelectric equation and the structure of the piezoelectric transducer used in this paper, we formulate the output voltage in terms of the four mechanical quantities, i.e. the radial strain and axial stress of the transducer as well as the acoustic pressure and the radial displacement of the borehole fluid. Furthermore, the contributions of these four mechanical quantities to different wave groups are explored. Finally, the waveforms comparisons after drill collar grooving reveal that the displacement waveform before and after grooving should also be displayed when evaluating the grooving effect instead of only the pressure waveform as in previous studies.

Failure Modes and Root-Cause Analyses of Advanced Drill-Collar Connections

Summary Advanced drill-collar connections have been developed with 10 times extended fatigue life compared with the corresponding replaced connections. More than 4,000 advanced connections have been run in North America. Although these connections have demonstrated substantial fatigue-strength improvement in operation, some failures have occurred. Multiple failed connection samples have been retrieved and analyzed for their failure modes and the root causes. In the failure analyses, manufacturing data were reviewed to identify any possible discrepancies between design specifications and manufactured components. The field run data were analyzed for the loading histories of the connections. The downhole fluid properties were also reviewed to identify their possible effects on the connection performances. The bottomhole assemblies (BHAs) were numerically analyzed to determine the loading distributions. The failed connection samples were physically processed and inspected in a metallurgical laboratory. Based on the combined numerical and testing analyses, the conclusions on the failure modes and the root causes were drawn. It was found that the primary failure mode for these connections was fatigue. The root causes for the fatigue failures can be divided into two categories: manufacturing causes and operational causes. Among the manufacturing failure causes, incorrect cold rolling is the primary one. The operation-related failures were mainly caused by overloading. Through failure mode and root-cause analyses, the manufacturing and operational related risks for the advanced drill-collar connections were mitigated accordingly. It therefore greatly improved the quality assurance of the advanced connections.

Failure Modes and Root Cause Analyses of Advanced Drill Collar Connections

Advanced drill collar connections have been developed with 10 times extended fatigue life compared with the corresponding replaced connections. More than 4,000 advanced connections have been run in North America. Although these connections have demonstrated substantial fatigue strength improvement in operation, some failures have occurred. Multiple failed connection samples have been retrieved and analyzed for their failure modes and the root causes. In the failure analyses, manufacturing data were reviewed to identify any possible discrepancies between design specifications and manufactured components. The field run data were analyzed for the loading histories of the connections. The downhole fluid properties were also reviewed to identify their possible effects on the connection performances. The bottom hole assemblies were numerically analyzed to determine the loading distributions. The failed connection samples were physically processed and inspected in the metallurgical laboratory. Based on the combined numerical and testing analyses, the conclusions on the failure modes and the root causes were drawn. It was found that the primary failure mode for these connections was fatigue. The root causes for the fatigue failures can be divided into two categories: manufacturing causes and operational causes. Among the manufacturing failure causes, incorrect cold rolling is the primary one. The operation related failures were mainly caused by overloading. Through failure mode and root cause analyses, the manufacturing and operational related risks for the advanced drill collar connections were mitigated accordingly. It therefore greatly improved the quality assurance of the advanced connections.

Influence of flex-sub on mechanical properties of rotary steerable drilling system

In this paper we analysis of the dynamic model of the Rotary Steerable System (RSS) with a single stabilizer and flex-sub. The drill collar and joint are simplified to obtain suitable bottom-hole assembly (BHA) model of mechanical analysis and finite element analysis. Using the BHA uniform stiffness assumption (ignoring the influence of variable section and variable stiffness of drill collar in BHA), the paper takes a method of the longitudinal and transverse bending continuous beam method to analyse the stress of BHA with RSS with the flex-sub under different inclination angles and curvature conditions. In addition, a dynamic analysis model is proposed, and the dynamic stress of drilling tools with RSS is analysed. Through the software of ANSYS, the finite element analysis of the RSS with the flex-sub is carried out to verify the theoretical results. The influence of flex-sub on the steering drilling performance of RSS is studied, and the optimized parameters of flex-sub design are obtained, which provides useful suggestions for the design of RSS.

Minimum gas injection of gas drilling while temperature and pressure coupling

Gas drilling technology not only has the advantages of avoiding well leakage, shale hydration expansion,reservoir pollution and other issues, but also can greatly improve the drilling speed 4 to 8 times, it is helpful to timely discover and effectively protect reservoir and improve recovery efficiency and single well production of oil and gas reservoir, especially has important significance for hard strata and dense reservoir exploration. However, there are some problems hindered the promotion of this technology, such as gas is hard to carries cuttings and gas hole blocking. One of the key technologies to solve these problems is the determination of gas volume. Most of today’s literature use formation temperature instead of annulus temperature to calculate minimum gas volume. Owing to gas’ PVT effect, temperature is dramatically influenced by pressure flow velocity, there will be big error if we use formation temperature instead of annulus temperature. Meanwhile, most of traditional minimum gas volume methods use top of the drill collar as key point. In this study, we found that on the top of the drill collar, the carrying kinetic energy of gas is not is not necessarily the minimum, and change of the key position is strongly influenced by wellbore structure and make-up of drill tool. Minimum gas volume determined by applying temperature - pressure coupling calculation is more close to site construction, under the given conditions, error of the minimum gas volume is about 0.4%.

Studying of speed on the process drill string flattening vertical wells

The issue of vertical wells curvature is important, especially when conducting wells in complex geological conditions of drilling, due to the increasing depth of the wells and the corresponding rise in the cost of drilling. The cause of this circumstance lies in the large time and financial costs while flattening of the bent wells. Moreover, it should be noted that during the subsequent drilling of a curved well the risk of key-seating and the corresponding complications increases. That is why large oil field service companies and drilling enterprises are paying more and more attention to solving the problem of vertical wells curvature. This article is devoted to investigation the effect of rotation of the drill string on the deflecting force on the bit while drilling a vertical well in a rotary way. We suggest using of eccentric drill collars for drilling vertical wells in difficult geological conditions. Also, we create an expression for the dynamic milling force on the bit, taking into account the usage of an eccentric drill collar in the composition of bottom-hole assembly.

EVALUASI NILAI CUTTING CARRYING INDEX PADA LUMPUR DIESEL OIL

<em>Evaluation of Cutting Carrying Index when using Diesel Oil base mud in well T is carried out on section 12-1 / 4 ", 8-1 / 2", and 5-3/4 ". This is because the use of mud on the previous section did not use Diesel Oil base mud, but only used native mud and KCL Polymer base mud. In the CCI evaluation of the Diesel Oil mud, several parameters included, Equivalent Circulating Density and rheology of diesel oil base mud. Based on the primary data on well T the ECD calculation can be done by calculating the average annulus velocity, velocity critical around annulus hole, and the pressure loss in it. The value of ECD obtained on section 12-1 / 4 "ranges from 14 ppg to 15 ppg, section 8-1/2” has 16,08 ppg to 16,4 ppg, and section 5-3 / 4" reaching 14,72 ppg as the biggest value. Based on the ECD, CCI value is obtained, this is because the ECD value describes the mud weight around the annulus hole. A good CCI value must be greater than or equal to 1, then evaluated with the results of CCI on route 12-1 / 4 "obtaining the greatest CCI value 1.6 in the jar and drill collar I. On route 8-1 / 2", CCI value evaluated in the heavyweight drill pipe section with a change in the value of 0,76 to 1,08. The CCI value on section 5-3 / 4“ changes in value from 0,65 to 1,19 in heavyweight drill pipe section.</em>

Research on a rotational speed control strategy of the mandrel in a rotary steering system

Rotary steering systems are cutting-edge, intelligent oil drilling and steering equipment developed at the end of the twentieth century. The core function of the bit pointing rotary steering system is to control the eccentric shaft with bit pointing function to track the outer drill collar for reverse rotation [1]. When the relative speed thereof is offset, the mandrel tool face remains stationary, and the directive function of the drill bit is realized [2]. Therefore, it is important to precisely control mandrel rotational speed and make it follow the outer drill collar to conduct face-to-face rotation at all times. A double closed loop control method for realizing rotational speed loop and position loop through controlling mandrel rotational speed is proposed in this paper. Relative rotational speed of drill bit shaft (or mandrel) and drill collar of zero can be realized within the shortest time, thereby realizing rapid and precise rotational speed tracking. Relative positions of mandrel and drill collar at several angles on 360° circumferences, thereby proving the feasibility of the method. The method can provide a technical reference and basis for prototype production of directional rotary steering system [3].