In-Situ Stress Orientation Determination Using Differential Strain Analysis And Palaeomagnetic Orientation

In the exploration and development for oil and gas reservoirs, in-situ stress orientation is becoming more and more important. The surface of natural fracture (crack) is parallel to the orientation of maximum principal stress. The principle orientation of anisotropic permeability reservoirs agrees with the orientation of the maximum principle stress. Many engineering problems (e.g.bore-hole stability, casing deformation failure during drilling, reasonable arrangement of wells, the optimum design of hydraulic fracture and so on) are influenced by the in-situ stress orientation. Therefore, the study of in-situ stress is very important in the exploration and development.A convenient and reliable technique being used for studying the in-situ stress orientation is a key problem concerned by petroleum engineers. So far, many methods have been used for studying the in-situ direction of oilfields and every method has its advantages and disadvantages. This thesis focuses on the method that predicts in-situ stress orientation for wells using differential strain analysis (DSA) and palaeomagnetic orientation.Differential strain analysis (DSA) method being used for determining the direction of the maximum principal stress with respect to the master orientation line (MOL). The original orientation (i.e. the MOL with respect to the geographical north) of the core in the formation can be obtained by palaeomagnetic orientation tests. The two results are combined to define the direction of the maximum principle stress of the well or field.On the basis of the research of home and abroad and the actual situation of our company and the demand of oil fields, the theory, tests and application in fields of the technique were studied. Some conclusions are drawn.1. The theory and method of the technique are correct and ripe.2. Before the DSA tests, sample preparation is the key for a successful test. To get reliable data, core processing and strain pages selection are operated strictly.3. During sample preparation for palaeomagnetic reorientation, the proplem of magnetic pollution which is produced by other magnetic field should be cautions .4. The examples in abroad and home indicate that the viscous remanent magnetization is a convenient tool for orientation determination of drilled cores. It can be used on samples for which the geological age is not known. The only information required is well position, the direction and magnitude of well deviation and the 'right way up' for the core sample.5. During the research on the method of development and fracture in low permeability reservoir, the results from the DSA and palaeomagnetic tests were analyzed and compared with the results of other methods. Then the syntheticalresults were used for the well-web design in the low-permeability experimental area. The good developing results and economic benefit are produced when the well-web design was operated. It's indirectly proved that the oriented method is a reliable and practical. Moreover, the natural fracture direction tested by the underground microseismic monitoring system also proved that the orientation technique is correct and comparable.6. The technique which predicting in-situ stress direction for wells using DSAand palaeomagnetic orientation has been applied in wide-range---Daqing, Jilin,Shengli, Anhui, Henan, Erlian, Changqing,Talimu and Qinghai oil fields and so on. The results of application are very good.In short, the method is convenient, economic and reliable and the result applied in the oil fields seems reasonable. It can provide reliable basis for the predication of the fracture orientation and the design of development.It should be pointed out emphatically that further research should be done, such as the problem on the anisotropic core. We still emphasized that several different methods used for stress orientation determination in the field to get a reasonable data and provide a reliable basis for the design and application.