ABSTRACT: Based on the theory of the limit equilibrium method of slope stability analysis, this article studied the infinite slicing calculate theory under the circumstance that the loess slope sliding-plane does not cross the slope foot. Through the formula derivation, the analytic formula of the sliding torque Mr, and resisting moment Mf were calculated, and then it was concluded that the safety factor K is function of the smooth arc radius R, the sliding body string angle a and angle of slope plane distance Δl. We simplified the process of searching the most dangerous sliding surface on genetic evolution method reasonably and effectively. On the basis of concept of replication, hybridization, variation, competition and selection in biological genetic evolution steps, in the process of the most dangerous sliding surface search, change the two-way variation for one-way and increase mutant genes of the slope angle of plane distance. While other factors remain unchanged and only one of the factors changes, the minimum safety factor was computed under the restrictive condition and its applicability was determined. After changing another factor and repeating the searching process, the minimum safety factor and the corresponding value of various factors were figured out finally. Realizing search on the most dangerous sliding-plane does not cross slope foot. Also, we used FORTRAN software program to complete the compilation of the search procedures. The engineering examples have confirmed that this method is feasible and safe. This paper has important value of reference to improve the loess slope stability analysis theory.
At present, the theory of the limit equilibrium method is the main approach to analyse slope stability. However, it simplifies the boundary conditions of the landslide.
Different assumptions lead to various theory of limit equilibrium method of slope stability analysis.
The common theories are Bishop, Janbu, Spencer, Morgenstern-Prince and so on.
For various limit equilibrium methods stand for different hypothesis, they make remarkable effect on results and precision.
At the same time, these methods have complete and meticulous theoretical derivation. Because the methods themselves make some simplifying assumptions. Thus some unavoidable limitations and the final results are often different from the engineering practice, which may leads to low precision of results because we can only rely on the experience of slopes. In view of that, particularly on loess areas, it's eager to make an intensive study of each past theory to draw more precise limit equilibrium methods of slope stability analysis to guide the project. Moreover, it could reduce disasters of engineering to secure the safety of people's life and wealth.
Peng, C. (University of Science and Technology Beijing) | Guo, Q. S. (University of Science and Technology Beijing) | Zhang, Z. C. (University of Science and Technology Beijing) | Zhao, L. (University of Science and Technology Beijing) | Yan, Z. X. (University of Science and Technology Beijing)
ABSTRACT: With the increase of the slope height in open-pit mines, the contradiction between the mining safety and stripping quantity becomes progressively serious. According to the analysis and calculation, the original slope angle in Gaocun Iron mine is conservative. After engineering geological investigation and rock mechanical tests, three optimization schemes were proposed. FLAC3D numerical simulation software was used to analyze the slope stability by several indexes such as displacement and plastic zone. In addition, the safety factors were obtained according to the limit equilibrium method by Geo-slope software. Eventually, the final slope angle of the mine was determined. It showed that the optimized slope angle is improved by 3° compared with that of the former design on the whole, and the slope stability well meets the requirement of production.
There are a growing number of metal mines carrying on deep mining in our country, and the design of open pit slopes faces a dilemma in that situation: When the slope angle is too big, the steep slope will cause instability and failure, which is not conducive to the normal production of the mine; In contrast, the small angle will increase the stripped amount and the production costs significantly. To solve this problem, slope angle must be optimized on the premise of mining safety (Heok & Bray 1981, Duncan & Christopher 2005).
Gaocun pit of Nanshan Mining Co., Ltd., is a large open pit mine, whose ore production has reached 7 million tons per year with the total mining and stripping of 18 million tons. After entering the second phase of open pit mining, the north-south length of the stope expands from 780 m to 1500 m, and the east-west width expends from 575 m to 820 m. The highest level of open pit mining is up to +90 m and the bottom elevation is down to-186m. Under the conditions of high and steep slope mining, with mining depth increases, the contradiction between security and economic production is gradually highlighted. Therefore, slope design must be optimized to ensure the production safety and increase economic efficiency.
Davila, Wilfredo (Baker Hughes Inc.) | Azizov, Azar A. (Baker Hughes) | Janwadkar, Sandeep Shashikant (Baker Hughes) | Jones, Anthony (Baker Hughes Inc.) | Fabian, John A. (Baker Hughes) | Rowan, Thomas (BJ Services Company)
Although drilling horizontal wells in US-land unconventional shale plays has increased exponentially in the last few years, maximizing well productivity and improving drilling efficiency remains a major challenge. Well placement in the sweet spot and extended laterals help maximize productivity. Drilling a curve with higher dogleg severity (DLS) reduces its verticalsection and maximizes the length of subsequent lateral section in the productive zone. Wells in US shale plays demand a DLS of 10 to 14 deg/100 ft, but achieving high DLS presents numerous drilling challenges: rotating a steerable motor with a high adjustable kick-off sub (AKO) angle could result in bottomhole assembly (BHA) fatigue failure and premature damage to bit; drilling in oriented mode limits the transfer of weight to the bit, reducing the rate-of-penetration (ROP).
These challenges led to the development and successful testing of a new steerable optimized design motor (ODM) with a short bit-to-bend (BTB) distance. In some cases, the ODM drilled all sections, including high-DLS curves, tangents and laterals with precise directional control and well placement with one BHA. Using the ODM helped the operator achieve higher build rates at lower AKO angle settings; rotate the BHA in well profiles where previously used motors could be operated only in slide mode, and maximize the length of curve interval drilled in rotary mode at higher rotations per minute (RPM). The new system significantly improved drilling performance with excellent directional control. Drilling high-DLS curves increased the length of laterals, enabling additional recovery of gas.
This paper discusses the design, modeling and results of horizontal type wells drilled using the steerable ODM in the Marcellus unconventional shale play.
Jones, Anthony (Baker Hughes Inc.) | Azizov, Azar A. (Baker Hughes) | Janwadkar, Sandeep Shashikant (Baker Hughes) | Davila, Wilfredo (Baker Hughes Inc.) | Fabian, John A. (Baker Hughes) | Nguyen, Minh Thanh (Range Resources Corp)
Although drilling horizontal wells in US-land unconventional shale plays has increased exponentially in the last few years, maximizing well productivity and improving drilling efficiency remains a major challenge. Well placement in the sweet spot and extended laterals help maximize productivity. Drilling a curve with higher dogleg severity (DLS) reduces its verticalsection and maximizes the length of subsequent lateral section in the productive zone. Wells in US shale plays demand a DLS of 10 to 14 deg/100 ft, but achieving high DLS presents numerous drilling challenges: rotating a steerable motor with a high adjustable kick-off sub (AKO) angle could result in bottomhole assembly (BHA) fatigue failure and premature damage to the bit; drilling in oriented mode limits the transfer of weight to the bit, reducing the rate-of-penetration.
These challenges led to the development and successful testing of a new steerable optimized design motor (ODM) with a short bit-to-bend (BTB) distance. In some cases, the ODM drilled all sections, including high-DLS curves, tangents and laterals with precise directional control and well placement with one BHA. Using the ODM helped the operator achieve higher build rates at lower AKO angle settings; rotate the BHA in well profiles where previously used motors could be
operated only in slide mode, and maximize the length of curve interval drilled in rotary mode at higher RPMs. The new system significantly improved drilling performance with excellent directional control. Drilling high-DLS curves increased the length of laterals, enabling additional recovery of gas.
This paper will discuss the design, modeling and results of horizontal type wells drilled using the steerable ODM in the Marcellus unconventional shale play.
Menand, Stephane (DrillScan US Inc) | Simon, Christophe (DrillScan) | Gerbaud, Laurent (Paris School Of Mines) | Ben Hamida, Malek (Schlumberger) | Denoix, Henri Jean (Varel UK) | Cuillier, Bruno (DrillScan) | Gaombalet, Jerome (Total S.A.) | Amghar, Youssef (VAREL) | Sinardet, Hubert
The footage drilled with rotary steerable systems (RSS) has increased significantly these last few years, due notably to the highly complex wells drilled today. Moreover, high requirements about borehole quality are needed to optimize drilling performances, running completion tools or increase the quality of formation evaluation.
Rotary steerable systems can be classified in two types according to the steering mechanism: point-the-bit and push-the-bit. Whatever the type of steering mechanism, both tilt and side force are applied on the bit. Although bit tilt is predominant in point-the-bit system, bit side force is the main factor that affects hole deviation in push-the-bit system. There have been many controversies in the scientific and industrial community regarding the deviation mechanisms involved in these two systems. To react to this controversy, a full-scale drilling bench has been developed to test drill bits in push-the-bit, point-the-bit or hybrid push-point mode. This new facility enables to apply any coupled tilt-side force on the bit to reproduce the RSS mechanisms.
This paper is intended to show results of this experimental campaign. First, the role of the side force and of the bit tilt in the deviation process have been fully differentiated and measured . Then, these results demonstrate that the bit steerability for a same given side force is strongly affected by the tilt applied on it. At last, one shows that borehole quality is not only affected by the bit design itself but also by the tilt-side force combination These experimental results presented in this paper have been validated with a software that enables to reproduce the hole deviation every inch drilled. The results of this paper should also contribute to improve bits selection for RSS in order to drill a smooth and uniform borehole.
The Luno discovery in the Norwegian sector of the Southern North Sea, with an estimated 180 million recoverable barrels of oil (Greater Luno area including Tellus) in a conglomerate and sandstone reservoir, has proven to create unique drilling challenges. The reservoir, planned with horizontal or 60° slanted producers and inclined water injectors, consists of both sandstones and conglomerates with granite clasts of varying sizes.
During the exploratory phase the conglomerate was mainly cored with diamond impregnated bits. The recorded rate of penetration (ROP) through the conglomerate spanned from 0.5- to 3.5-m/hr; for most of the time it stayed at between 1- and 2-m/hr. Reduced well cost was one of the early identified major potential field development savings if the conglomerate can be drilled with polycrystalline diamond compact (PDC) bits capable of an ROP of 10- to 15-m/hr, and which would last for 500- to 1000-meters reservoir sections.
To investigate the feasibility of using PDC bits, after reaching the target in appraisal well 16/1-13, the well was deepened utilizing two different types of PDC test bits. After the PDC field tests were conducted with the first bit ringed out after 70 meters and the second bit partially worn out after 34 meters of rough drilling, it was decided to initiate a PDC development project to develop a PDC bit with cutters that could withstand the challenging drilling of the conglomerate for the upcoming field development/production phase. A "conglomerate pie?? test block was manufactured and used in a vertical turret lathe to conduct single cutter PDC testing.
Utilizing the improved wear and impact resistance of the new enhanced cutters developed based on results from the testing, an experimental bit with different cutter types was used in another well with hard basement rock. From the cutter and bit performance observed during the field test, further laboratory- and field testing was conducted with these cutters showing preliminary performance results of 3- to 4-times initial durability potential for a constant ROP.
One of the key objectives within the drilling industry is optimizing rate of penetration (ROP) and a major contributor to obtaining this objective is the PDC bit design. Whilst previous papers have proven that the PDC cutting structure geometry, particularly back rake and side rake angles, affect PDC bit performance when tested at atmospheric conditions, no information in the SPE literature exists for similar tests at confining pressures. The effect of side rake angle on cutter aggresiveness and cutter interaction at depths of cut (DOC) in excess of 0.04?? are particularly unknown under confined pressure.
The results of more than 150 tests show that back rake and side rake angles have substantial effects on Mechanical Specific Energy (MSE) and the aggressiveness of PDC cutters. Experiments with three different rock types; Carthage marble, Mancos shale, and Torrey Buff sandstone, revealed that at both atmospheric and elevated confining pressures, PDC cutters with 10 deg back rake angles require half the energy to cut the same volume of rock and produce higher cutting efficiency compared with cutters having 40 deg back rake angles. Possible reasons for this behavior are explained through the analysis of the cutting process.
Results show that a cutter with low back rake requires less horizontal cutting force in order to cut the same volume of rock. This observation indicates that not only will a PDC bit with lower back rake angles, drill more efficiently, but it will also require less torque in order to drill at the same ROP. Other factors such as reduced durability of cutters at low back rake angles should also be considered while applying these results to PDC bit designs.
Test results at both atmospheric and confining pressures revealed that MSE decreases with increasing DOC up to 0.08?? on all three rock types. However, the tests also showed that MSE starts to increase slightly at DOCs above 0.08??, possibly suggesting an optimal minimum DOC.
Experimental results also show that, whilst Mancos shale and Carthage marble have about the same compressive strength, Mancos shale requires three times less energy to cut compared to Carthage marble. This indicates that, compressive strength of some rocks such as shales cannot be used alone as a reference rock property for accurately evaluating and comparing drilling efficiency.
A new 3D mechanistic PDC cutter-rock interaction model was also developed which incorporates the effects of both back rake and side rake angles, along with rock specific coefficient of friction. The results from this single-cutter model are encouraging as they are consistent with the experimental data.
Shinmoto, Yuichi (Japan Agency for Marine-Earth Science and Technology) | Miyazaki, Eigo (Japan Agency for Marine-Earth Science and Technology) | Wada, Kazuyasu (Japan Agency for Marine-Earth Science and Technology) | Yamao, Masaoki (Japan Agency for Marine-Earth Science and Technology)
Core sampling is one of most important methods for gaining knowledge on formation properties below the seafloor or for extracting such potential new energy resources as methane hydrates. The riser-equipped deep-sea drilling vessel Chikyu carries out scientific expeditions for such underwater formation core drilling to analyze the origin of hydrate generation near the coast of Japan. Among the various systems available, continuous coring using wireline is the most promising for obtaining a steady supply of core samples.
Although measuring-while-drilling/logging-while-drilling (MWD/LWD) methods are deployed, an advanced directional control system specifically for deep-sea coring is currently under technical development. Core barrels consisting of the inner and outer barrels have been designed with an inner barrel that is retrievable and resettable. The new method combines an adjustable bent-housing sub that is located between the outer barrel and just above the inner core tube.
Laboratory tests in which the inner barrel is passed through the bent housing section have been performed, with results showing bent housing angles of 0.25-2.0°. Land drilling tests with the bent housing were also performed in order to ensure drilling efficiency and core recovery. This paper presents the progress of our newly developed coring system with an integrated analysis of directional-drilling and coring capabilities.
Alekseenko, Olga Petrovna (Schlumberger Technology Corp.) | Potapenko, Dmitry Ivanovich (Schlumberger) | Cherny, Sergey G. (Institute of Computational Technologies, Siberian Branch of Russian Academy of Sciences) | Esipov, Denis (Institute of Computational Technologies, Siberian Branch of Russian Academy of Science) | Kuranakov, Dmitry (Institute of Computational Technologies, Siberian Branch of Russian Academy of Science) | Lapin, Vasily (Institute of Computational Technologies, Siberian Branch of Russian Academy of Sciences)
A 3D numerical model of fracture initiation from a perforated wellbore in linear elastic rock is developed, which allows one to determine the fracture initiation pressure (FIP) and the location and direction of an initial rupture. The model assumes that the fracture initiates at the point where the local maximum tensile stress exceeds the rock tensile strength. The 3D boundary element method is used for stress analysis.
The model is aiming at predicting the location of initial fractures and the difference in FIP between different perforation intervals in arbitrarily oriented non-cemented wellbores. There are many practical applications where this knowledge is required, but of particular interest for this research is the employment of differently oriented perforations for creating heterogeneity of FIP between wellbore intervals in multistage fracturing treatment. This can enable stimulation of these intervals in a sequential mode and significantly simplify current treatment diversion and completion practices.
Comprehensive analysis revealed that the main parameter that can be used for controlling FIP during multistage fracturing treatment is the angle between the direction of the perforation channel and the preferred fracture plane. The model allows obtaining the range of the angles that is the most suitable for designing and implementation of diversion between the perforated wellbore intervals. The influence of geometrical parameters of perforation (e.g. length, diameter and shape) on FIP is substantially less. Addtionally we found that against all expectations increase of perforation diameter can result in higher FIP. It was also discovered that the influence of the intermediate in-situ stress on FIP is comparable with the effect of perforation misalignment especially in the situation of horizontal wellbore and properly aligned perforations. Based on the model developed, an approximate approach to the evaluation of the impact of wellbore cementation on fracture initiation was suggested. It was discovered that taking into account the state of stress within the cement prior to well pressurization can result in both an increase
and reduction of FIP depending on the parameters of perforating as well as wellbore orientation.
The presented model is the necessary step toward predictable and controllable fracture initiation, which is vital for multistage fracturing treatment diversion.