The CAD/CAE system of a tricone rock bit

Transcription

1 Computer Aided Optimum Design in Engineering IX 453 The CAD/CAE system of a tricone rock bit Z. Wu 1, V. Thomson 2, H. Attia 2 & Y. Lin 1 1 Department of Mechanical Engineering, Southwest Petroleum Institute, P.R.China 2 Department of Mechanical Engineering, McGill University, Canada Abstract The purpose of this paper is to introduce the CAD/CAE system of a tricone rock bit especially to rock bit designers. The system is integrated with Pro/Engineer (one of best CAD/CAE/CAM commercial software in the world, also called Pro/E), and operated in the Drawing mode of Pro/E. The system is composed of three parts: 2D intermesh design (including parameterised insert section and slots modelling), simulation and optimal design, and the engineering database. One important characteristic of the system is its ability of arranging an insert on the intermesh design of a tricone rock bit with linkage function, which is very useful for engineers. In addition, the function of simulation and optimal design helps designers to greatly shorten the design cycle. A case study shows that the CAD/CAE system can improve the performance of the tricone rock bit and will bring magnificent social and economic efficiency. The system can also output contour data of three cones for 3D solid modelling of the tricone rock bit, which is a basis for the CAM of the tricone rock bit. Keywords: CAD/CAE, tricone rock bit, simulation, intermesh, optimal design. 1 Introduction Tricone rock bit is an important tool in oil and gas drilling, and accounts for a large number of shares in the rock bit market of the world. Therefore rock bit engineers have been looking for better ways to make rock bits faster, more efficient and more durable. The cutting structure of tricone rock bit interacts with rock directly, and its performance affects the rate of penetration (ROP) greatly. Thus it is the key object that we study. Before microcomputers are widely used, designing bits is usually based on repeated trial and individual experience of bit engineer, which

2 454 Computer Aided Optimum Design in Engineering IX takes designers much time. During this period, some papers about kinematics and dynamics of rock bit were published [1,2,3]. These theories and research results form the fundamental of the first generation CAD of tricone rock bit. After that, the CAD system improved continually. However the design speed is still slow because of the complexity of tricone rock bit structure [4]. Therefore it is very essential to develop more reasonable and efficient CAD system of rock bit, especially about intermesh design. With all sorts of challenge and competition from companies, the CAD technology, especially Computer Aided Optimal Design, becomes indispensable means for any enterprise to innovate its technology and exploit the product market. Pro/Engineer, one of the most excellent 3D CAD/CAM systems, is applied worldwide with its characteristics of parametric design. But it is rarely reported publicly that dedicated application software about 2D intermesh design of rock bit has been developed under Pro/E environment up to now. Therefore, this paper introduces the application software about 2D CAD of tricone rock bit developed with Pro/Toolkit (API tool provided by Parametric Technology Corporation). In addition to the CAD of rock bit, we also develop CAE of tricone rock bit. By the end of last century, Ma had done a great deal of research about simulation of interaction between rock bit and rock [5]. Now the simulation software is enriched greatly by the writer of this paper. It can simulate the kinematics of tricone rock bit and also conduct optimal design on the intermesh design, which can shorten the design cycle greatly. In accordance with the above CAD and CAE, an engineering database is also developed with SQL Server2000 and Delphi. 2 Overall design and main function modules The CAD/CAE system includes three parts as follows: 1) the 2D Intermesh Design, including insert section modeling and automatic insert positioning with linkage function; 2) the Simulation and Optimal Design, which can simulate the interaction between bit and rock and get loads on inserts and ROP; 3) the Engineering Database, which can deal with a great of data related to the bit structure, rock properties and other movement parameters. The operating system and the support software are Windows2000 and Pro/Engineer2001. The developing tools include Pro/Toolkit2001, VC++6.0 and Delphi6.0, and SQL Sever D Intermesh Design CAD/CAE of Tricone Rock Bit Simulation and Optimal Design Pro/E2001, Pro/Toolkit, VC++6.0,Delphi6.0 SQL Sever2000 Windows2000 Engineering Database Figure 1: Schematic of system structure.

3 Computer Aided Optimum Design in Engineering IX 455 From Fig 1, we know that the bottom level is operating system, then database server and other supported commercial software are as intermediate levels, and the top level is the CAD/CAE system interface for users D intermesh design of tricone rock bit The fundamental of drawing transform Assuming that ( x, y) and ( x ', y ' ) are the coordinates of a point before and after the transform respectively, T x and T y are the increment of the point along horizontal and vertical coordinate axis respectively, andθ is the rotation angle, so the formulas of the transform for transplantation are x ' =x+t x and y ' =y+t y, and for rotation are x ' =xcosθ -ysinθ and y ' =ysinθ +ycosθ. The whole transform matrix is as the following: cosθ sinθ 0 [ x ' y' 1]=[ x y 1] sinθ cosθ 0 (1) T x T y Parametric geometry models Insert section model We compute all key points of an insert section, and connect them to form lines and arcs, then make them a block, finally move and rotate the block to required place. Fig 2 is section draft of two types of inserts. There are some key nodes on each insert section and each point s coordinate expressions are listed in table1 and table2. D, h, H, SR, R, α denote diameter, cylindrical height, height of insert, spherical radius of the top of conical insert, radius of the top arc of chisel insert and half cone angle respectively. Figure 2: Insert models (Left: conical insert, Right: chisel insert) Slot section model Constructing a slot model is somewhat more complicated than creating insert models. Divide the slot into two parts: one is composed of two lines that are connected with two inserts, and the other is the

4 456 Computer Aided Optimum Design in Engineering IX middle section between the two lines (Fig 3). The slot model is rotated to angle Ag between the horizontal line and the centreline of cone. We also compute all key points of the slot model and create lines and arcs, then make a block, finally move and rotate to desired place. Dd1and dd2 are sunken depth of crown of insert 1 and insert 2 respectively. Jd1, jd2, jd3 and jd4 are angles. Ds1, ds2, ds3 and ds4 are wall thickness of two insert holes. R1 and R2 is arc radius. Dh is the height of the slot. Table 1: Key nodes for conical insert. Node No. X-coordinate Y-coordinate 1 X 1 Y 1 2 X 2 =X 1 +D Y 2 =Y 1 3 X 3 =X 2 Y 3 =Y 2 +h 4 X 4 =X 1 Y 4 =Y 1 5 X 5 =X 4 +tt*cos(m) Y 5 =Y 4 +tt*sin(m) 6 X 6 =X 3 -tt*cos(m) Y 6 =Y 5 Centre of Arc X c =X 1 +D/2 Y c =Y 1 +H-R Here tt= (D/2) + (H - h - R) - R m=tan -1 (R/tt)+tan -1 (2(H-h-R)/D) Table 2: Key nodes for chisel insert. Node No. X-coordinate Y-coordinate 1 X 1 Y 1 2 X 2 =X 1 +D Y 2 =Y 1 3 X 3 =X 2 Y 3 =Y 2 +h 4 X 4 =X 1 Y 4 =Y 1 5 X 5 =X 4 +Wtanα Y 5 =Y 4 + W 6 X 6 =X 5 +Rcosα Y 6 =Y 1 + H 8 X 8 =X 3 -Wtanα Y 8 =Y 5 7 X 7 =X 8 -Rcosα Y 7 =Y 6 Centre of Arc X c1 =X 6 Y c1 =Y 5 -Rsinα Where W=H-h-R(1+sinα ) Horizontal line Insert 1 Insert 2 Centreline of cone Figure 3: A sort of slot model.

5 Computer Aided Optimum Design in Engineering IX Intermesh design After having created the above two models, we can realize 2D intermesh design of tricone rock bit. The module has three functions. a) The envelope curve of all inserts breaking rock on well bottom can be obtained (Fig 4). b) The key technique during the 2D intermesh design of the tricone rock bit is solved. That is, if you move or rotate any insert with mouse, the other two inserts (in fact it is the same insert) in the same window change positions correspondingly (Fig 5). We often use three colours to represent inserts of three cones respectively: cyan is for cone one, yellow for cone two and green for cone three. Rotation and translation of an insert is easily done by means of mouse. The realization of this technique depends on correct translation and rotation transform matrix, which guarantees the same change of position of inserts. Finally 2D intermesh design of tricone rock bit can be obtained and the section geometry of three cones can be saved for 3D solid modelling (Fig 6). c) The intermesh clearance (or critical distance) between adjacent cones can be computed and output. Figure 4: Envelop curve of all inserts. Figure 5: Arrangement of inserts with linkage. 2.2 Simulation and optimal design Computer simulation is a new technology or method that can solve practical engineering problems with fast development of computer science technology. One of its main characteristics is "experimentation". It can solve some problems that are not solved with other methods or means [6]. We also call it last method.

6 458 Computer Aided Optimum Design in Engineering IX In the past ten years, we have developed a set of simulation software for designing and analysing rock bits (Fig. 7). They are used in some rock bit companies (for example, Smith International Inc. of USA). Now we have integrated the software with the above intermesh design module under Pro/Engineer environment into a CAD/CAE system. At the same time, we add optimal design to the CAD/CAE system. Our emphasis here is not put on studying design search methodologies and optimisation algorithms but application of known optimum methods (for example, Conjugate Gradient Method). The optimum design is applied on performance analysis of tricone rock bit. The objectives are to get the maximum ROP under the same drilling parameters. The design variables include position angles of inserts on each row, offset value and journal angle of the bit. The main constrains are: diameter of the bit is a standard value and the loads on inserts of each row are less than the specified values. However we can t consider all the rows, because that will take much time to simulate the drilling process. Therefore we must first find out main rows that play an important role in fracturing rock. After getting main rows of the bit, we can enter into optimum design module. After all parameters of main rows are input, the software can run automatically and save necessary results into the database. According to a lot of simulation experiments, we know that the objective function has multi-extremum phenomena. Therefore the software can output the former ten maximum values and corresponding optimal parameters so that we can make a trade-off from their combinations. The simulation and optimal design can shorten the design cycle of rock bit and also improve its performance in the mean time. Figure 6: 2D intermesh design. Figure 7: Simulation of tricone rock bit.

7 Computer Aided Optimum Design in Engineering IX Engineering database The database mainly includes fundamental parameters of rock bits, drilling parameters, rock properties, geometric parameters of 8 types of inserts and analysis results. The database is loaded in a server and different people have different authority to access it. A control interface can access the server by means of ODBC and have the function of inputting, saving and extracting all sorts of parameters and results, which is bridge between simulation system and Pro/Engineer The support software is SQL Server 2000, VC++6.0 and Delphi Case study We are going to improve the performance of an old tricone rock bit F. The objective is to increase the volume of rock broken by main rows on the bit. Table 3: Rock Volume Broken (cm 3 ) Comparison of breaking rock ability of old bit and new one. Cone 1 Cone2 Cone 3 Row 1 Row 2 Row 1 Row 2 Row 1+2 F GF Percentage added 156.0% 12.5% 86.2% 1.03% 13.8% Here we use the CAD/CAE system to finish the improvement design or optimal design and the results are shown in the table 3. From the table, the modified bit GF (or new bit) has a good increase in volume, which means will have a higher ROP than the old one. Generally speaking, the bigger the ROP, the better the bit s performance under the same drilling conditions. The system has been used in main bit companies and research institutes of China. There is no doubt that it will bring magnificent social and economic efficiency. 4 Conclusions It is the first time that 2D intermesh design of tricone rock bit is integrated with Pro/Engineer. The intermesh design module realizes an important function, that is, when you move or rotate any insert in intermesh drawing, the same inserts in the drawing of envelop curve change to corresponding positions. The integrated CAD/CAE system with optimal design can shorten the design cycle and improve performance of rock bit. Overall, The system is an advanced design and analysis tool for rock bit designers. References [1] D. Ma, J.J. Azar, A Study of Rock-Bit Interaction and Well bore Deviation, Transactions of the ASME, Vol. 108, September 1986, p

8 460 Computer Aided Optimum Design in Engineering IX [2] D. Ma, THE OPERATIONAL MECHANICS OF THE ROCK BIT, Petroleum Industry Press, Bei Jing, P. R. China, February 1994, p [3] D. Ma, D. Zhou, R. Deng, The Computer Simulation of the Interaction Between Roller Bit and Rock, 1995, SPE 29922, p [4] D. Ma, J. Hou, New Design Method of Rock Bit. Proceedings of International Conference on Petroleum Engineering 1992, SPE [5] D. Ma, Z. Wu, Computer Simulation of TriCone Rock Bit's Breaking Rock, Proceedings of Simulation Technology of Automation Association of China, 1997 p [6] Y. Feng, Systematic Simulation and its Application, Machinery Industry Press, May, 1992 p2-10.