1999 Vol. 5, No. 1

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WELLBORE STABILITY ANALYSIS OF EXTENDED REACH WELLS
JIN Yan, CHEN Mian, LIU Gonghui, CHEN Zhixi
1999, 5(1): 6-13.
Abstract (371) PDF (157KB)(24)
Abstract:
Stability of extended reach wells is an important subject. Instability problems like lost circulation and borehole collapse during drilling operation lead to poor hole conditions causing a lot of problems like poor cement displacement and others. As a result, excessive nonproductive time and expensive wells are experienced.
This paper is based on a linear elastic and isotropic mechanics models for stress distribution around extended wells, with the aim of improve understanding the general behavior of extended wells. According to the established stability mechanics models, a wellbore stability simulator is developed, which runs under Microsoft Windows with friendly interface, high efficiency of field problem analysis. By using the software, the influence of certain factors on wellbore stability is analyzed. These factors include in-situ stress state, deviation, azimuth, strength rock, mechanical property and mud performance. Finally, the guide to determination of the azimuth and the safe mud density range for extended reach wells is presented.
LIQUID-SOLID COUPLED PROBLEM OF RADIAL FLOW THROUGH POROUS MEDIA UNDER GENERAL PLAIN STRESSCODITION
XU Zenghe, XU Xiaohe
1999, 5(1): 14-18.
Abstract (183) PDF (139KB)(23)
Abstract:
Taking into account the behavior that the permeability of deformable porous media varies with their porosity, the liquid-solid problem of liquid flowing through porous media under general plain stress condition is discussed.First the goveming equations are published, then a decoupled method is proposed, and the fields of pore pressure, the stresses, strains and displacement of media are derived analytically.The computation of cases indicates that there are obviously difference between the coupled analysis and non-coupled analysis.
THE PROBLEMS OF FLUID-SOLID COUPLING AND ITS ADVANCE IN RESEARCH
DONG Pingchuan, XU Xiaohe, HE Shunli
1999, 5(1): 19-28.
Abstract (321) PDF (158KB)(15)
Abstract:
In traditional seepage theory it is assumed in general that the medium or the solid skeleton through which the fluids flow is perfectly rigid, that is, the solid frame containing the fluids does not deform either elastically or plastically due to the pressure of the incumbent fluid. The coupling between fluid flowing and porous media deforming is generally neglected in past and fluids flowing through porous media was studied as non-coupled problems. Although this simplified assumption gives results to a first approximation this does not conform to the field practice and there are problems, for example, in oil production from oil reservoirs can lead to decreases in the pore pressure. This depletion results in changes of the effective stresses acting in the reservoir and in the deformation of the reservoir. Recently, the important significance of the fluid-solid coupling in porous media is generally recognized. Due to the importance of the coupled problems, considerable effort has been devoted in many engineering applications such as geothermal energy production, underground waste disposal, and oil production. These applications in engineering, especially in oil reservoirs are first introduced systematically. To counter the oil and gas exploitation, the fundamental method and the advance in research of the fluid-solid coupling in oil reservoirs are reviewed, and the future applications of the theory of fluid-solid coupling are also proposed.
FUNDAMENTAL EQUATION AND FINITE ELEMENT MODELING FOR OIL AND GAS MIGRATION DRIVED BY CRUSTAL STRESS
WANG Lianjie, WANG Wei, ZHANG Lirong, YUAN Jiayin
1999, 5(1): 29-34.
Abstract (303) PDF (115KB)(14)
Abstract:
In this paper are described first the differential equation and finite element formula for fluid migration under the action of crust stress in a porous rock. Then the oil migration potential field in Liaohe oil field are calculated by using finite element method based on crustal stress measurement. The result shows that most prospective oil fields are in low migration potential areas and transition areas from low to high migration potential. The study combining oil migration with tectonic analysis may provide the basis for exploration and development of oil and gas field.
CALCULATION OF ELASTOPLASTIC DEFORMATION OF WELLBORE IN SOFT MUDSTONE USING LAGRANGIAN METHOD
DENG Jingen, LIU Shujie, SHI Deqin, ZHANG Li
1999, 5(1): 35-39.
Abstract (213) PDF (106KB)(7)
Abstract:
In this paper we presented a review on the current situation of mechanical stability of wellbore in mud-shale bed and for the first time introduced large deformation theory into the calculation of elastoplastic deformation of wellbore and adjacent rock.Using Lagrangian method, we analyzed the problem of borehole shrinkage in mud-shale bed. Lagrangian method could solve the problem of material nonlinearity and geometry nonlinearity.In this paper we analyzed the calculation model using Lagrangian method with commonly adapted Mohr-Coulomb strength criterion, and solved the problem of wellbore shrinkage, the displacement field and the plastic region distribution of the wellbore and its adjacent rock.
NUMERICAL SIMULATION OF STRESS AROUND BORE HOLE
Liu Jie, Song Huizhen, Wang Yujie, Zhang Yiyuan
1999, 5(1): 40-46.
Abstract (248) PDF (139KB)(19)
Abstract:
In this paper, the distribution of in-situ stress and the changed stress field after boring are studied. By use of three-dimensioal FEM and a adaptive boundary load, an outlying oil field of Daqing is modeled as an example. The results, including stress direction, the relationslip between stress and depth, are coincident with measured in-situ stress of East China. Then we get a rule that with the same ratio of radius and the distance from hole center, the calculated stresses are same. Based upon these, we enlarged hole radius and use 3-D FEM to calculate the stress around borehole. The changed stress field is coincident with the observed collapse of bore hole.
A STUDY ON 3-D FINITE ELEMENT INVERSE MODEL
ZENG Hairong, SONG Huizhen
1999, 5(1): 47-51.
Abstract (230) PDF (178KB)(9)
Abstract:
Based on 3-D joint-element, the theory and methodology are discussed about inversion of geodetic data. The important FEM and inversion formula are given in detail; also a related code is developed. By use of this program, a FEM model is tested, which verifies the validity of the method here presented.
NUMERICAL SIMULATION OF STRESS FIELD IN RESERVOIR
YIN Youquan, CHEN Hu, JIANG Tian, SHAN Wenw en
1999, 5(1): 52-61.
Abstract (224) PDF (378KB)(16)
Abstract:
This paper gives two methods to simulate a stress field in the reservoir. The first method is that some measured stress data and the model of a three-dimensional membrane element are used to detemine the far field stress boundary condition with a back analysis and thereby to evaluate the stress field in the reservoir. The second method is a direct interpolation to evaluate the stress field with a moving least square method. A feasibility of these methods are discussed in the paper. To use the methods we simulate the stress field of Sanjianfang reservoir in Shanshan oil field and obtain a lot of good results.
NEW NUMERICAL SIMULATION METHOD OF ROCK FAILURE PROCESS UNDER ROCKBURST AND EXCAVATING
QIAO He, TANG Chun'an, LI Xiao, CHEN Rongde
1999, 5(1): 62-66.
Abstract (209) PDF (177KB)(9)
Abstract:
The nonlinear deformation of rock is caused by heterogeneity and anisotropy.A newly developed numerical code, RFPA (2D) (Rock Failure Process Analysis), is applied to study of failure process of rock under excavating, and macroscopic non-linear behavior of rock may be caused by continually fracturing of micro-element with elastic-brittle character. The reason which causes micro-element continually fracturing (fracturing not at the same time)is the non-homogenous character of micro-element material, such as microelement's strength, elastic modulus and Poisson's ratio, etc.RFPA (2D) is a relative simple compater method on math, but the complication of rock material is considered enough.
Laboratory Study on Effect of Hydration to Shale Mechanics
LU Baoping, LIN Yongxue, ZHANG Chuanjin
1999, 5(1): 67-72.
Abstract (259) PDF (128KB)(11)
Abstract:
On the basis of analyses of wellbore unstability mechanism, the changing law of shale mechanics parameters was established after shale hydration by the experimentation. The results from contrasts of collapsing pressures between unhydrated shale and hydrated one indicate that collapsing pressure for shale which behaves poor water sensitivity can be increased on a large scale, and verify the phenomenon exists that shale is stable in early contact with drillng fluid and turns out to be unstable later.
LABORATORY TEST METHOD STUDY OF DEEP ROCK PHYSICAL MECHANICS
ZENG Lixin
1999, 5(1): 73-77.
Abstract (223) PDF (91KB)(14)
Abstract:
Using the triaxial rock mechanics testing unit manufactured by American MTS Co, rock strength and deformation behavior are studied. The test results of core specimens show that rocks with the same lithologic properties indicate different deforming behavior while rocks with different lithologic properties similar curves of stress vs. strain due to the influence of weakness planes and filling on the rock, considering the influence of rock nonlinearity, reservoir condition and rock structure behavior, it is necessary to treat the test results based on the study range.
A ATTEMPT OF QUANTITIVE PREDICTION OF NATURAL CRACK ON BRITTLE ROCK RESERVOIR
SONG Huizhen
1999, 5(1): 78-86.
Abstract (166) PDF (193KB)(12)
Abstract:
This paper consists of four parts:(1)According to the Griffith theory of brittle strength the formulae of a criterion of failure were derived by author under the stress field (convention is that the tensile stress is positive) and applied them to analysis of the natural crack for reservoir; (2)Three numerical models and computative method of the quantitative analysis for paleo-stress as well as a method of the quantitative prediction for paleo-naturil crack were given in the reservoir of the carbonate rock; (3)A concept of effect tensile stress was presented a description of the natural tensile crack was provide for reservoir; (4)To provide a predicted tensile crack distribution map for reservoir of the carbonate rock and test it through drilling holes.
INSITU STRESS MEASUREMENT BY A METHOD USING ORIENTED CORE
LI Hong, CHEN Jingsong, JIANG Nansheng, WANG Fujiang, ZHANG Bochong
1999, 5(1): 87-91.
Abstract (240) PDF (117KB)(36)
Abstract:
A borehole was drilled in granodiorite rockmass at Fangshan, Beijing, China. The depth of the borehole is 301m with diameter of 110mm. From about 30m to 301m, all cores were oriented by cement end cap method. AE Kaiser effect tests on oriented core at depth of 294m were carried out. The rock specimens are the cylinders with 30mm diameter and 75mm height. In vertical direction, the vertical stress estimated by AE Kaiser effect tests is 7.7 MPa. The lithostatic pressure at the depth of 294m in granodiorite rockmass is 7.9 MPa. Both of them are almost same. In horizontal plane, for four directions rock specimen, AE Kaiser effect tests were carried out and their corresponding normal stresses were gotten. The horizontal maximum and minimum principal stresses are 21.2 MPa and 12.1 MPa respectively. The orientation of horizontal maximum principal stress is about the NStrending. Comparing the result of AE Kaiser effect tests with hydrofracturing shows that they are consistent fundamentally.
PALAEOMAGNETIC ORIENTATION OF CORES AND ITS APPLICATIONS FOR INSITU STRESS MEASUREMENTS
HOU Shouxin, TIAN Guorong
1999, 5(1): 92-98.
Abstract (207) PDF (243KB)(19)
Abstract:
A core from a certain depth is marked with a master orientation line (MOL), and is made into standard samples, which are used in palaeomagnetic tests and differential strain analysis (DSA) in the laboratory. The original orientation of the core in the formation can be obtained by magnetic cleaning test, magnetic parameter measurement and data processing. Differential strain analysis (DSA) method, which is used to determine the direction of the maximum principle stress with respect to the master orientation line, is combined with the results of magnetic tests to define the direct of the maximum principle stress in the area.

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