Experimental results on acoustic communication through drill strings using a strain sensor receiver

Efficient hole cleaning during drilling operations is critical to maintain a high rate of penetration and smooth drilling, leading to minimum drilling problems and economical drilling efficiency. This process involves several important factors, including pipe-sticking incidents, higher cuttings concentrations in the annulus, noisy vibration of the drill string, erratic equivalent circulating density, lost circulation incidents, well control incidents, geomechanical hole section instability, tight spots during tripping operations, and excessive usage of chemical additives for conditioning hole sections and mud. Various approaches, including correlations, methodologies, developments, algorithms, equipment, charts, field experience, chemicals, and studies involving experiments, can be used to enhance the efficiency of hole cleaning. The development of hole-cleaning models is important for use as hole-cleaning indicators to ensure optimized drilling efficiency. This paper presents a comprehensive overview of the complex field of hole cleaning in the oil and gas industry. It includes techniques, tools, models, and chemical additives. It also encompasses drilling engineering, operations, and chemistry. To facilitate the transit of drill cuttings, maintain hole section stability, cool and lubricate the drill bit, and transmit hydraulic horsepower, this article outlines the important roles of drilling fluids. The significance of chemical additives, including nanoparticles, natural and modified polymers, and synthetic polymers, in preserving wellbore stability, improving drilling efficiency, and lowering drill bit wear is also covered in the study. It concludes by making recommendations for further study to clarify hole cleaning for the reader to facilitate and boost drilling efficiency.

Many, perhaps most, who drill oil wells, know something about two-cone bits. These bits, for example, received the first cone bit patent nearly 100 years ago, yet, they have been popular in certain drilling environments within the last 20 years or less. Designers have always recognized great advantages in two-cone bits, but concerns with vibration, directional responsiveness, drilling straight holes, mechanical reliability, and hole cleaning lead to their displacement by three-cone bits. Unfortunately, two-cone bits have not, fully lived up to their potential. People have changed, and this has triggered changes in research philosophy. This together with technology advances in complex mathematical modeling, simulations and drilling processes has encouraged bit manufacturers to re-visit some older designs and learn to harness the potential inherent in those designs without their ill effects. This evolution has encouraged numerous step changes in drill bit technology. Could new people, new engineering and new manufacturing tools and tolerances, and a new sophistication at the rig finally unlock the potential of two-cone bits? To date, numerous runs with a modern two-cone bit design have taken place in Texas, Louisiana and internationally. Some of these runs are reported in this paper, detailing lessons learned and successes from the new two-cone bit that have been shared by the operators. Offset bits were one basis for performance evaluation and offset comparisons are also reported. In a direct offset well, a single modern two-cone bit drilled an interval, for which four offset bits were required (estimated savings: $342,000). Operator evaluations, performance outlines, information on reliability, bit vibration, directional responsiveness, deviation free performance, and hydraulic aspects of bottom hole cleaning, free of bit-balling, in several types of applications are included. The process and technology involved in designing the two-cone bits are identified in this paper. The lessons learned in planning between highly experienced drilling operators and bit company personnel toward overcoming paradigms and apprehensions in developing test plans for the improved technology are also discussed.

As development of deep oil reservoir, more and more deep and ultra-deep wells, of which the chief lifting method is sucker-rod pumping system, are drilled. There often exist problems for systems above such as high load and low pumping efficiency. Because of low density and high intensity of carbon fiber rod, polished rod load can be decreased by using carbon fiber rod to increase safety factor. Meanwhile, since elastic modulus of carbon fiber rod is low, stroke loss will be increased by unreasonable lifting parameters. Test of carbon fiber rod was conducted in Xinjiang oil field in order to verify the feasibility of carbon fiber rod in deep oil wells and evaluate load shedding and energy saving effect. To lighten field test workload, a 3D rod mechanical model was built to simulate conditions of different production parameters. From the results of field test and simulation, it is indicated that carbon fiber rod owns better load shedding capacity and higher strength intensity; under the condition of deep wells, more stroke loss may be caused by carbon fiber composite rod. For some conditions, pumping efficiency is low, even worse, rod lock problems like gaslock may appear; reasonable combination of rod string and production parameters can improve the feasibility of carbon fiber rod.

When drilling oil wells, drill-pipe strings are the main components that constrain reliability and efficiency of drilling rigs. The highest number of drill-string failures is caused by pipe parting. It is suggested that pipe-parting failures are preceded by the formation of a portion having a through-thickness radial lengthwise cut or a notched portion with a smaller cross-sectional area. Neither lengthwise cut nor crack in the rod can be determined using natural frequencies of longitudinal or flexural vibrations, because in the zone of the cut there is no reduction of the area and axial moments of inertia in the rod’s cross section. Therefore, this article deals with natural torsional vibrations of a drill string having damages as a through-thickness radial lengthwise cut and as a lateral notch. It has been found that in the case of the cut or the notch located within the vibration node, natural frequencies do not depend on the lengths of these damages. As the length of the cut or the notch increases, the lower frequencies of natural torsional vibrations will decrease. For the drill-string lengthwise through-thickness cut, changes in the natural torsional vibration frequencies are considerable as compared to similar frequencies for the drill string having a lateral notch. Using two natural torsional vibration frequencies, we can determine the initial coordinate and length of the through-thickness radial lengthwise cut on the drill string. Using three natural torsional vibration frequencies, we can determine the coordinate, length and parameter of the notch.

Corrosion problems of deep well tubings and their control measures are discussed. As one of the economical solutions, metal-lined tubings are proposed. It is shown that the metal liner can be tightly fitted by the newly developed thermo-hydraulic fit method. The selection of corrosion-resistant material for the liner is discussed. Some designs of the tubing joint and their manufacturing methods pre proposed. Introduction With the seriousness of an energy shortage, the drillings of oil and gas wells have become more active. In the last few years, the number of drilled wells has increased rapidly as shown in Fig. 1. It should be noted that eighty percent of these wells were drilled in the United States. Fig. 2 shows the depth distribution of oil and gas wells drilled in the United States in 1977. It can be seen that the numbers of oil and gas wells are about the same, but, in general, there are more gas wells at deeper depths than oil wells. As shown in Fig. 3, well depth increases each year, and recently an exploratory well deeper than 10,000 m has been drilled. As the well depth increases, the down hole pressure and temperature rise. For instance, in some severe wells at a depth of 6,000 m, the pressure and temperature are more than 1,000 bar and 200°C respec. tively. Therefore, the strength of the tubings used in such severe conditions is a very important factor for deep wells because they have to sustain their ownweight also. Figure 4 diagrammatically illustrates the transitions of design conditions with the increaseof well depth. Figure 5 shows the relationship between well depth and axial and hoop stresses of API standard tubings with various pipe 'dimensions. It isknown roughly that the strength of class P-I05 is required for the tubing of a 6,000 m well. Another substantial problem in deep oil and gas wells is corrosion. This is mainly due to H2S and C02 which are contained in crude oil and natural gas The density of these contaminants is increased with well depth, and, together with high pressure and high temperature, the corrosion reaction is accelerated. To solve all the above problems in deep wells, a new type of economical, high strength tUbing which has high corrosion resistance is expected. At present a super Ni alloy tubing, which is extremely expensive, tends to be used. As a solution, the authors propose the Tight Fit Tubing (hereinafter referred to as TFT) which is lined inside with corrosion-resistant alloy to meet the above three requirements for the tubing of deep wells. The thermo-hydraulic fit method used here for TFT has been developed to produce the corrosionresistant pipe, TFP, for corrosive flow lines as reported in Ref. 1.

Deep wells are commonly drilled while steering the drill bit. The steering process is completely controlled by the drilling-rig operator. A key element of this procedure is the measurement and communication of navigation information from the bottom of the well to the operator. Pressure pulses modulated onto the flow of the drill fluid are now employed in some cases to communicate this information. However, data rates are only a few binary bits per second with this method. This drastically limits the quantity of data available to the operator. As an alternative method, elastic waves generated within the steel drill string can be used as a carrier signal to transmit data. The drill string is commonly assembled from 10-m segments of threaded pipe and forms a periodic structure. The elastic wavelengths of interest are shorter than this periodic length. Consequently, these waves undergo significant dispersion. This paper presents new data for the propagation of elastic waves in a 2-km drill string. The influence of aperiodicity in the drill string, rotation of the drill string, and noise levels are studied in detail. The data verify a method for reducing the attenuation of a carrier signal by a factor of 2.

Real-time monitoring of mechanical specific energy and bit wear using control engineering systems

In the process of oil and gas drilling, the drill bit is the direct tool to break rock. The selection of drill bit needs to consider formation factors, drilling construction factors, field size requirements and other factors. At present, the optimization methods mainly include mechanical analysis, cost analysis, neural network method and other methods, but there are some limitations. In this paper, three categories and more than ten kinds of input parameters are selected, and the rate of penetration is predicted by BP neural network algorithm. Then, the bit library is established according to the actual bit used in the field, and the parameters of the bit are optimized by intelligent optimization process, and the actual demand is taken as the constraint to select the most suitable one. The error of the ROP prediction model was within 10%, and the ROP was increased by 11.67% on average with the optimized bit. In this paper, the rock breaking rule and complex mechanism of drill bit are stored in the model, and the drill bit optimization is carried out according to the actual requirements, which can provide a certain degree of support for the field drill bit optimization. INTRODUCTION With the development of oil and gas resources to deep and complex formations, the number of horizontal wells drilled continues to increase. At the same time, the horizontal well drilling area continues to expand, and complex geological conditions in some areas are revealed, and hard, highly abrasive formations are prevalent in most blocks. To a certain extent, the drilling operation progress is slow, the single drill bit is less advanced, and frequent drilling and replacement are required, which increases the non-drilling time and consumables consumption, thereby increasing the drilling cost. At the same time, as the length of the horizontal section continues to increase, the construction is becoming more and more difficult. This puts forward higher requirements for drilling construction, especially for the feed and life of a single PDC drill bit, the life of drilling tool combination, the adaptability of drill bit and drilling tool combination and formation. If the drill bit can be reasonably selected according to the formation characteristics, construction requirements, engineering parameters and other factors, so that the ROP and single drill bit advance greatly increase, and even achieve a single drill (only 1 drill bit per spud), it will greatly improve drilling efficiency and reduce drilling costs (Fear et al., 1994). However, as the use of PDC drill bits increases year by year, more new varieties and models of PDC continue to appear, and their scope of use continues to expand. Moreover, there are many parameters of PDC drill bits, which are more sensitive to formations, and slight changes in drill bit parameters may produce large effect differences. Therefore, how to establish the relationship between drill bit parameters, formation anti-drilling characteristics and construction parameters, and refine and optimize drill bit is a problem to be solved.

Bit feed principles and operations of slide drilling

This paper deals with the development of a novel mesoscopic model of polycrystalline diamond compact (PDC) drill bits that can be implemented in complex drill string models for simulations to analyse the influence of rock inhomogeneities or the impact of anti-whirl bits on drill string dynamics. In contrast to existing modelling approaches, the model is developed at a mesoscopic level, where the basic bit–rock interaction is taken from the macroscopic bit model and the cutting characteristics are summarised at a microscopic cutting level into a simplified configuration via cutting blades. This model can therefore effectively describe asymmetries and thus interactions between the torsional and lateral dynamics of the drill bit, and is particularly suitable for investigating the effects of drilling into rock inhomogeneities and fault zones on drilling dynamics. By integration into a complex drill string model, simulation studies of drilling through a sandwich formation were carried out. The simulation results allow detailed stability statements and show the influence of formation properties and bit design on torsional and lateral drill string dynamics.

The drilling of oil wells is one of the most expensive steps in oil exploration. It requires a high initial investment and it offers an uncertain economic viability. Thus, laboratory tests seek to optimize the process and reduce costs, accidents, and damage to the reservoir. Furthermore, computational calculations and simulations offer more precision and agility in data evaluation, reducing even more the costs and duration of the tests. In this study, a computational model was created to evaluate the drill fluid leak in a permeable rock formation. A fluid was inserted into the reservoir during the well drilling to load debris from the porous domain helping the drill bit. The porosity of the rock formation allows the entry of drill fluid, which can cause environmental damage, can lead to additional expenses, and can derail the well. The objective was to create a model with time-based parameters to conduct the evaluation of the influence of flow parameters. Thenceforth, the simulations allowed observing the high influence of permeability gradients to the profiles of invasion.

Effective control of shale swelling and lost circulation using drilling fluid is considered the dominant strategy for maintaining borehole stability, especially drilling operations in deep oil and gas wells. In this work, a hybrid silicate that contains lithium silicate and potassium methyl silicate (PMS) was employed as a film-forming additive to reduce shale hydration and filtration loss in the high-temperature drilling fluid. Scanning electron microscopy (SEM) results revealed that a dense quartz crystal film coating on the shale can be formed in a hybrid silicate solution when the temperature exceeds 150 °C. The in situ-formed film on the shale surface with a thickness of 60–130 μm was composed of fibrous crystalline silica. Furthermore, the aqueous hybrid silicate exhibited enhanced hydration inhibition ability by preventing water invasion of the formation. Aqueous hybrid silicate with a concentration of 0.5–3 wt % lithium silicate and 0.1–0.2 mol/L PMS was first chosen to obtain the optimum concentration according to the hydration inhibition ability and film formation characteristics. The hybrid silicate was added into a drilling fluid formulation applicable in high-pressure and high-temperature conditions, and the rheological characteristics and filtration properties were investigated. The results confirmed that drilling fluids with the addition of hybrid silicate can mitigate variation of viscosity and yield point before and after aging at 180 and 220 °C. Besides, the filtration behavior was also improved by adding hybrid silicate into the drilling fluid. A lower filtration loss was observed at the concentration of 1.0 wt % lithium silicate and 0.2 mol/L potassium methyl silicate, which showed 63 and 50% HPHT fluid loss reduction for unweighted and weighted formulations at 205 °C and 3.5 MPa, respectively. In addition, the drilling fluid featured stable rheological and filtration properties and excellent shale hydration inhibition characteristics when exposed to high temperatures, making it a promising candidate for drilling in deep oil and gas wells.

Electromagnetic (EM) telemetry is one of the key research subjects that has increased application in transmitting real-time data between the borehole and surface during drilling. There are several methods that can be used to model an EM telemetry system, including the method of moments (MoM) and the electric field integral equation method. We have developed a pulse basis function for the MoM, which assists in the analytical estimation of thin wire kernel integrations and avoids singular problems when simulating current distributions. The scattering field is solved using the current distribution. We examine the method using a simple example of vertical drilling. In the model, a vertically placed drill string is driven through a layered earth model. The drill string represents a long, thin wire antenna with a source located near the drill bit. The validity of the method is confirmed by comparing our results to the analytical solution in a half-space model as well as the current distributions along the drill string derived from the proposed method with those derived from a commercial finite-element solver, COMSOL-Multiphysics. Furthermore, the efficiency of this method is demonstrated by comparing its computational costs with those of COMSOL. The simulated EM telemetry in a known geologic setting is then compared with a field data example. These comparisons show that the proposed method is accurate and efficient. Moreover, we develop insights into how the parameters needed for calculations alter current distributions along the drill string and the signal received at the surface. The proposed method is therefore useful for obtaining the optimal design parameters for EM telemetry systems.

Part of the process of exploration and development of an oil field consists of the drilling operations for oil and gas wells. Particularly for deep water and ultra deep water wells, the operation requires the control of a very flexible structure which is subjected to complex boundary conditions such as the nonlinear interactions between drill bit and rock formation and between the drill string and borehole wall. Concerning this complexity, the stick-slip phenomenon is a major component related to the torsional vibration and it can excite both axial and lateral vibrations. With these intentions, this paper has the main goal of confronting the torsional vibration problem over a test rig numerical model using a real-time conventional controller. The system contains two discs in which dry friction torques are applied. Therefore, the dynamical behaviour were analysed with and without controlling strategies.

Effective communication in oil wells is challenging because of partially-conductive soil and rock, and inhomogeneities in the ground. An alternative approach to communicating with the drill head, or electronics associated with it, is to use the drilled hole itself as a path for communication. The typical well hole is cased with a steel lining and surrounded by air or cement. The electrically-conductive casing, along with a second conductor consisting of the earth itself, acts like a dielectric waveguide used in fiber optics to guide light. The earth is not very conductive, but as long as it has a different dielectric constant than air, it can act to guide waves axially through the gap between the steel and the ground.