Borehole Trajectory Research Articles

Development of an adjustable stabilizer for controlling the borehole trajectory

Development of an adjustable stabilizer for controlling the borehole trajectory

Temperature field analysis on the highly-deviated wellbore in backwashing condition

Based on the measured borehole trajectory, a prediction model of temperature field of highly-deviated wells in backwashing condition is established. To verify the model, a test instrument to measure the temperature variations in the wellbore is developed and used to measure the temperature of two typical highly-deviated wells in backwashing condition. The comparative analysis shows that the wellbore temperature predicted by the model is close to that measured in field with the relative error less than 8%. The model was further used to analyze the influence of liquid-injection speed and injection time on the temperature distributions of oil pipe, annulus space and radial direction under the backwashing operation with original-temperature and hot washing liquid. It is found that for the backwashing operation with original-temperature washing liquid, the temperature at the lower part of the shaft is most affected by the displacement rate and backwashing time, whereas the curve section and the lower part of the shaft are most affected by the displacement rate and backwashing time in hot washing operation. Along the depth of the borehole, there is a constant temperature section which is almost unaffected by displacement rate and backwashing time. The radial heat transfer analysis shows that the heat exchange range is not large and near the wellbore.

Directional deflection equations for steerable drilling tools and the control mechanism of wellbore trajectory

To meet the wellbore trajectory control requirements for all kinds of steering drilling modes, the directional deflection equations for steerable drilling tools and the process control method for wellbore trajectory were proposed and an application example was given. By proving that the orientation direction of steerable drilling tool was consistent with the principal normal direction of borehole trajectory, directional deflection equations for steerable drilling tools were established. By establishing the relation curves between the build-up rate and tool face angle, and the relationship between built-up rate and orientation azimuth angle of steerable drilling tool, a process control technique for wellbore trajectory was presented. The research shows that the build-up rate of steerable drilling tool determines the curvature of wellbore trajectory, the orientation direction of steerable drilling tool determines the principal normal direction of wellbore trajectory; the orientation azimuth angle and the tool face angle both have the orientation function, and they can calculate and complement each other. These research results reveal the interaction mechanism and control mechanism between steerable drilling tools and wellbore trajectory, so the control scheme of wellbore trajectory can be formed based on the planned wellbore trajectory, and operating characteristics of steerable drilling tool can be controlled and monitored while drilling.

Lithology mapping by a hybridization of the firefly and affinity propagation algorithms

The lithological identification of layers crossed by the borehole trajectory or the direct extraction of geological information from the well logs is a classic challenge in formation evaluation and has expressive impact over realistic values calculations for porosity and oil saturation. In this work we present a computer-aided interpretation of the M-N plot based on a new hybrid algorithm, which refines the affinity propagation clustering technique. For the optimization of clusters' searching, it is used a preference vector that flags affinity propagation with M-N points that are the possible best candidates to be the lithological classes representatives. These possible best candidates are obtained by a firefly metaheuristic optimization of a Kernel function, built over the M-N space. Finally, a minimum distance criterion, with respect to M-N mineral points is applied to the set of exemplary points acquired from this approach, in order to associate the lithologies. This methodology was applied in synthetic and real M-N data and in our tests, proves its effectiveness in producing a realistic lithological identification even for highly-spread M-N data.

Computer simulation of resistance force mitigation through curvature bridging in extended bore-holes

As is shown in scientific literature, the curvature discontinuity of a bore-hole trajectory can be one of the most influential factors in generation of friction forces resisting to motion of drill strings. To avoid the curvature discontinuities between the bore-hole sections, curvature-bridge curves in the shape of clothoid spirals were proposed for their smoothing. In this paper, it is shown that if the transient clothoid curve is short, the cubic parabola bridge can be substituted for it. As demonstrated below with the use of the elaborated stiff string drag and torque model, this curve has simpler geometry and is suitable for use of spline approximations. The impact of the curvature break smoothing on the resistance forces reduction is investigated for tripping in and out operations and different regimes, simulating drilling procedure. The cases of pure sliding, pure rotation and their combinations are considered for the 2D and 3D models of the bore-hole trajectories.

A true three-dimensional wellbore positioning method based on the earth ellipsoid

Abstract In view of the problems existing in the current wellbore positioning method, a true three-dimensional wellbore positioning method was presented, and an example for analysis was given. The current positioning method uses the grid north as the reference datum to the north, positions in the horizontal plane based on the map projection coordinates, and positions in the vertical direction based on the elevation coordinates. It has inherent defects and errors, as the two positioning methods above are independent of each other, and only use the constant meridian convergence and constant magnetic declination at the wellhead to calculate the borehole trajectory for the whole well. Based on the earth ellipsoid and its calculating principle, the transformation relationship between the wellhead coordinate system, geodetic coordinate system and elevation coordinate system was revealed, and the true three-dimensional wellbore positioning method using the true north as the reference datum to the north was presented. Analysis results of an example show that the current positioning method yields a smaller vertical depth and a larger horizontal displacement for the target, and produces larger errors compared with the true three-dimensional positioning method. The true three-dimensional positioning method has fundamentally solved the problems existing in the current positioning method, accurately positioning the relative location between the target and the wellhead, and significantly improves the accuracy and reliability of borehole trajectory design.

Elastic Bending Deformation of the Drill Strings in Channels of Curve Wells

The problem about identification of elastic bending deformation of a drill string in a curve wells based on the theory of flexible curved rods and the direct inverse problems of drill string bending in the channels of curvilinear bore-holes is stated. The problem is solved which determines the resistance forces and moments during performing ascending-descending operations in curvilinear bore-holes with trajectories of the second order curve shapes. The sensitivity of the resistance forces relative to geometric parameters of the bore-hole axial line trajectories is analyzed.

Treatment practice of sloughing and sticking in offshore deep wells with complex trajectories

A majority of adjustment wells drilled in eastern parts of South China Sea are characterized by big depth and complex borehole trajectory. In case of sticking incidents, forces for stuck releasing may not be transferred effectively, consequently, stuck releasing operations in these wells may involve huge difficulties. By analyzing root causes of sticking incidents in Well A in the offshore Lufeng 13-1 Oilfield in the paleogene enping formation, techniques such as stuck releasing through circulation and gradual lifting with minor discharging volumes have been developed to release stuck drilling tools effectively. These newly developed technologies may serve as fast and highly effective ways to remove problems related to sloughing and sticking in the area. In addition, these techniques may provide necessary guidance for dealing with sloughing and sticking problems in wells with similar conditions.

Borehole Stability in Mudstone Shale and Coal Seams in the Daniudi Gas Field

In order to study the reasons for borehole instability, we calculated the mud density window for horizontal wells in complex formations based on logging data. From the results of the mud density window calculation, we found that for mudstone shales it decreases as the inclination angle and the azimuth increase, while for coal it took on negative values. We found that collapse and expansion are conducive to maintaining borehole stability, while in coal seams a positive mud density window can be achieved only by collapse (a decrease in the borehole diameter). It was determined that we need to increase the mud density from 1.2 to 1.4 g/cm3 and use drill pipes that are as small as possible for the longest possible period of time. In this case, the borehole trajectory should be determined according to the seam location and the mud density.

Wellbore stability analysis for horizontal wells in shale formations

As a serious problem in drilling operation, wellbore instability restricts efficient development of shale gas, especially in formations with weak bedding planes which have strong strength anisotropies. The occurrence of bedding planes has significant influence on wellbore instability. Triaxial compressive tests have been carried out to study the effects of the orientation angle between the major principal stress direction and the weak bedding plane on the strengths of weak bedding shales. According to the laboratory test data, the strength of rock matrix and the strength of weak bedding planes were acquired, and failure criterion of rock matrix and weak bedding planes were established based on Mohr-Coulomb strength criteria. Based on the poroelasticity theory and rock strength theory, this paper proposed a wellbore instability analysis model for horizontal wells to reveal the combined effects of borehole trajectory, occurrence of stratification, strength of weak plane on wellbore instability. The results show that the shape of curve between peak compressive strength and orientation angle is ‘U-shaped’, and the bedding planes of weakness causing the strong strength anisotropies. When the bedding dip angle is greater than about 45°, the reasonable well azimuth angle would make wellbore stable. In addition, the directions of bedding planes and in-situ stresses pose the significant influences on wellbore instability. This paper provides a method for wellbore stability analysis of weak bedding formations which can help design mud density and well trajectory by elaborating all the effects of various parameters on wellbore stability.

A Review of the Evaluation, Control, and Application Technologies for Drill String Vibrations and Shocks in Oil and Gas Well

Drill string vibrations and shocks (V&S) can limit the optimization of drilling performance, which is a key problem for trajectory optimizing, wellbore design, increasing drill tools life, rate of penetration, and intelligent drilling. The directional wells and other special trajectory drilling technologies are often used in deep water, deep well, hard rock, and brittle shale formations. In drilling these complex wells, the cost caused by V&S increases. According to past theories, indoor experiments, and field studies, the relations among ten kinds of V&S, which contain basic forms, response frequency, and amplitude, are summarized and discussed. Two evaluation methods are compared systematically, such as theoretical and measurement methods. Typical vibration measurement tools are investigated and discussed. The control technologies for drill string V&S are divided into passive control, active control, and semiactive control. Key methods for and critical equipment of three control types are compared. Based on the past development, a controlling program of drill string V&S is devised. Application technologies of the drill string V&S are discussed, such as improving the rate of penetration, controlling borehole trajectory, finding source of seismic while drilling, and reducing the friction of drill string. Related discussions and recommendations for evaluating, controlling, and applying the drill string V&S are made.

Fracture analysis in borehole acoustic images using mathematical morphology

Fracture analysis is a geological task that treats so-called fracture attributes (location, direction (strike), slope (dip), and aperture) of the fractures that cross the borehole. It can be performed by direct measures on drill cores or interpreted on acoustic or electromagnetic images of the borehole wall. This activity has gained more importance in Brazil with the recent exploration of carbonate reservoirs of the Brazilian pre-salt. The acoustic imaging logging tool creates two images, the amplitude and the travel time. Only the amplitude image, which reflects the acoustic impedance of the borehole wall, is used to perform the fracture analysis. However, some misinterpretations may occur due to the qualitative nature of this interpretation being very dependent on the geologist’s expertise. Thus, we present a method of performing automation of the fracture analysis using acoustic amplitude images. This article is divided into two parts. In the first part, we present a mathematical model for the acoustic amplitude images along the borehole trajectory crossed by fractures. This model involves all fracture attributes in the generation of the images and is used to validate the results of fracture analysis. The second part presents the method for automatic fracture analysis. This method is composed of two stages. The first one performs fracture identification using an algorithm based on the mathematical morphology, which acts as an edge-detection tool that delimits the fracture region in the acoustic amplitude images. In the second stage, we apply an interpolating polynomial over the image region previously identified as fracture to extract the fracture attributes. The evaluation of this methodology is performed with synthetic images generated by the presented model that supports the results of the automatic fracture analysis performed using real acoustic amplitude images.

Advancement and economic benefit of geosteering and well-placement technology

In the development of many of today's reservoirs, the oil and gas industry is challenged to drill more efficiently and is asked constantly to maximize recovery and production. However, drilling through these reservoirs is challenging because geologic models often are limited to the resolution of seismic data, and offset wells often have significant variations. Geosteering is the process of adjusting the borehole trajectory in real time to correct for unanticipated variations in geology and structure to avoid exiting the target zone. It is a technique currently used on many horizontal and deviated wells for better well placement and for efficiently draining a reservoir. Recent improvements in well-placement and formation-evaluation technologies have helped in gaining access to bypassed reserves that originally were not thought to be practical targets. Examples highlight the economic benefit of geosteering and well-placement technology. Maximum reservoir contact in the sweet spot leads to increased production, and early warning of approaching faults and bed boundaries results in reduction of sidetracks. Furthermore, keeping the well trajectory away from the oil-water contact optimizes production by producing less water. Finally, maximizing production by placing the wellbore entirely within the best reservoir zone boosts productivity so that wells that previously appeared difficult or uneconomic are now becoming viable.

How do permeable fractures in the Triassic sediments of Northern Alsace characterize the top of hydrothermal convective cells? Evidence from Soultz geothermal boreholes (France)

The thermal regime of the Upper Rhine Graben (URG) is characterized by a series of anomalies near Soultz-sous-Forêts (France), Rittershoffen (France), and Landau (Germany). These temperature anomalies are associated with groundwater circulation in fractures and faults distributed in the Cenozoic and Mesozoic sedimentary cover associated with and connected to fractures originating deep within the Paleozoic basement. The present study helps to understand the convective cell structure in order to optimize geothermal borehole trajectories. The work concentrated on a detailed interpretation of the geophysical and geological logs from Soultz geothermal wells mainly from the topographic surface to the Triassic formations, at between 800- and 1,400-m depth above the deep granitic basement. The analysis of drilling mud logging data and geophysical well logging data from the deep Soultz geothermal wells (GPK-2, GPK-3, GPK-4) reveals the occurrence of nine fracture zones situated at depths greater than 900 m in the limestones of the Muschelkalk (Middle Trias) and the sandstones of the Buntsandstein (Lower Trias). Based on indications of total or partial mud losses, these fracture zones have been classified as permeable or impermeable. Permeable fractures between circa 900-m depth and 1,400-m depth are connected to a large-scale fault and control the top of the convective cells. There is no indication of permeability in the formations above the Keuper layer, and the uppermost part of the sedimentary cover acts as a cap rock, insulating the convective regime in the Triassic sediments and the granitic basement.

Constructive optimization of electrode locations for target-focused resistivity monitoring

Crosshole resistivity tomography has received consideration as a tool for quantitative imaging of carbon dioxide stored in deep saline aquifers. With regard to the monitoring responsibility of site operators and the substantial expenses associated with permanent downhole installations, optimized experimental design gains particular importance. Based on an iterative appraisal of the formal model resolution matrix, we developed a method to estimate optimum electrode locations along the borehole trajectories with the objective to maximize the imaging capability within a prescribed target horizon. For the presented crosshole case, these layouts were found to be symmetric, exhibiting refined electrode spacings within the target horizon. Our results revealed that a sparse but well conceived set of electrodes can provide a large part of the information content offered by comparably dense electrode distributions. In addition, the optimized layout outperformed equidistant setups with the same number of electrodes because its resolution was focused on the monitoring target. The optimized electrode layouts presented provided a powerful and cost-efficient opportunity to complement permanent installations, particularly at, but not limited to, future [Formula: see text] storage sites. Although preliminarily developed to support the design of crosshole resistivity layouts, our approach is directly applicable to other survey geometries including surface and surface-to-hole acquisitions.

Application of Moments in Qualitative Analysis on Borehole Trajectory Curving

There are many calculation methods of horizontal borehole trajectory, such as cubic spline interpolation function which is based on three-moment equation. By calculating the moments of deviation and azimuth from cubic spline interpolation function respectively, it is easy obtain functions of deviation and azimuth change rate and average borehole curvature to analysis on curving of borehole trajectory. So it is one of the most common methods. However, the moments are always be neglected. Moments of deviation and azimuth, which could be used to qualitatively estimate borehole trajectory curving, are first proposed tentatively in this paper. Synthetically employing other useful parameters of estimation borehole trajectory curving, tens of high-angle directional and horizontal wells’ drilling data is computed and analyzed. Contrast to the variation characteristics of deviation and azimuth change rate, the deviation and azimuth moments have the similar change tendency respectively. The results of this study signify that the proposed parameters could provide some reference for assessment on borehole trajectory curving.

The Analysis of Fluid Pressure Impact on String Force and Deformation in Oil and Gas Wells

Fluid pressure is a crucial factor to tubular string strength and deformation in oil and gas wells, and it is the most difficult factor to deal with. When the string constrained by downhole tools, such as packers, action pattern of fluid on string is changed. Calculation methods of string stress and deformation given by engineering handbooks doesn’t distinguish these issues in detail. So mistakes are often made when these methods are used. Tangled concepts lead to large calculation error. In this paper, the influence of fluid pressure on string axial force and deformation, buoyancy treatment in packed condition, are discussed roundly both in vertical wells and directional wells. Practical calculating method of string axial force through the hook load is presented, and element buoyancy in different borehole trajectory is given. It is found that the traditional simplified buoyancy coefficient method, which is used to calculate string axial force and axial extension, can only be used in vertical wells with tubular string suspended freely, because in this condition buoyancy acts on the bottom of string. If the string is constrained by downhole tools, such as packer or anchor, buoyancy could not be treated as usual. In directional well the buoyancy not only changes string axial force but induces shear stress in string cross section. When calculating the influence of fluid on string, operation sequence and constraints from borehole and downhole tools should be considered comprehensively.

New Analysis Theory and Method for Drag and Torque Based on Full-Hole System Dynamics in Highly Deviated Well

The research on calculation of torque and drag in highly deviated wells has demonstrated a significant gap against oil exploration and development; with the increasingly rigorous situation, the drill string dynamics and the contact or friction of drill pipe with borehole wall under the drill string action of dynamic need more attention and urgent research work. Based on full-hole system dynamics, three-dimensional nonlinear dynamic model and dynamic torque and drag model were established in highly deviated well by using the finite element method. An application of analyzing typical torque and drag problems presented here provides a means to more accurate description of the contact relation between drill string and wellbore. The results show that those models established in this paper have complete adaptability for a complex three-dimensional borehole trajectory. For the actual well application, it will help to evaluate security performance of drill string in complex working conditions.

Analysis of borehole collapse and fracture initiation positions and drilling trajectory optimization

Abstract For borehole stability analysis, it is of vital importance to correctly determine the borehole and fracture initiation postions; currently studying their variation rule, most of them are based on borehole stress solutions for plane stress condition, or neglects the influence of shear stresses. This research analyses the failure directions of deviated boreholes in different faulting stress regimes for plane strain condition with the polyaxial strength failure criterion Mogi-Coulomb and develops a new analytical equation of determining the optimum drilling trajectory. The analytical results show that Poisson׳s ratio generally exerts more influence on the angular positions of borehole collapse than fracture initiation positions with the exception of some cases where Poisson׳s ratio has no influence on the angular positions of borehole collapse and the borehole collapse and fracture initiation positions. It is not always correct to neglect the effect of shear stresses on the borehole collapse and fracture initiation positions with respect to particular cases; when drilling orientates along the direction of minimum horizontal in-situ stress in normal faulting stress regime, there is a range of inclinations where the borehole collapse and fracture positions are identical; moreover, the same circumstances will also take place in a direction parallel to the maximum horizontal in-situ stress in the reverse faulting stress regime or the borehole is horizontal with particular drilling orientation in the strike-slip faulting stress regime. The optimum drilling trajectory lies in the critical turning point, which corresponds to the aforementioned three situations, respectively, of angular positions of borehole collapse. Therefore, this study’s result can provide a theoretical basis for the optimization design of borehole trajectory and a safe drilling fluid density window.

Well-to-seismic tie of Amangihydrocarbon field of the Niger Delta of Nigeria

In this paper we performed seismic-to-well tie and wavelet extraction that would subsequently be used for inversion. We took cognizance of the key factors that make for accurate well-to-seismic tie and ensured that the borehole seismic and the surface seismic at the borehole trajectory look as similar as possible. This was possible through quality control of the well log and seismic data, timing and log calibration, well tie location, seismic bandwidth and signal-to-noise ratio and the use of well tie diagnostics that underlie a successful close well tie. The data were processed to zero phase and the dominant loop in the resulting seismic wavelet was delayed and corresponds to an increase in P-impedance. The delay on the seismic data was removed and the wavelet converted to zero phase. The ties are generally good and accurate. With this success we were able to relate directly the horizons picked on the 3D anisotropic seismic data to the well logs. We estimated the wavelets needed to invert the seismic data to impedance and rock property indicators.This was achieved by careful simultaneous analysis of the results at the wells to derive one average wavelet each for the near, mid and far angle stacks.