1、翻译部分In situ stress determination from inversion of hydraulic fracturing dataAbstractThe paper presents a new method, based on rigorous principles of mechanics, for determining the insitu rock stress state based on hydraulic fracturing data. A solution can be obtained from a single data set which inc
2、ludes breakdown pressure, fracture angular position and trace angle. The inversion methodology is demonstrated on a case history from the Kuparuk River eld, Alaska as reported by and is shown to give good agreement with observed eld data.Keywords:Hydraulic fractureIn situ stressInversionInclined wel
3、lbores1. IntroductionHydraulic fracturing is the best-known method of assessing the state of in situ stress at great depths. The technique originated in the 1940s as an oileld stimulation technique designed to intensify production by fracturing a segment of a wellbore through pressurization; the fra
4、cture was then extended by additional pumping and maintained open (or propped) by injecting solid particles such as sand grains or glass beads. Following the great success of hydraulic fracturing as a stimulation technique, attempts were made to understand the mechanisms behind it. The most importan
5、t effort in the interpretation of hydraulic fracturing mechanism was made by Hubbert and Willis who used the theory of elasticity to reach the conclusion that the direction of the induced hydraulic fracture and the pressures recorded during borehole pressurization are directly related to the princip
6、al in situ stresses. Fairhurst 3 was among the rst to advocate the use of hydraulic fracturing for in situ stress determination. Haimson and Fairhurst 4 extended Biots theory of poro-elasticity to include both non-penetrating and penetrating injection uid cases. Hydraulic fracturing has now become o
7、ne of the key methods for in-situ rock stress estimation as suggested by the International Society for Rock Mechanics (ISRM) A detailed history of the method and a thorough description of the equipment, setup, test data interpretation and in situ stress derivation are presented in Ref. 6.Although hy
8、draulic fracturing is commonly conducted in vertical holes, testing of inclined or deviated wellbores is often required. For example, in the petroleum industry inclined holes are increasingly used for added efciency in production. In geotechnical site investigations, exploratory inclined holes are o
9、ften drilled in order to intersect vertical joint sets which could be missed by vertical holes. Additionally, rock properties or drilling difculties may cause unintended deviated holes. A technique for inverting results from a minimum of two leakoff tests at different well inclinations and azimuths
10、was presented in Refs. 7,8. This method gives an estimate of both horizontal stress magnitudes and directions. However, the published technique suffers from the assumption that shear stresses are neglected. Gjnes et al. 9 present results based on a model thatalso includes the shear stresses. Djurhuu
11、s and Aadnoy 10 present a theory for determining the in situ stress state from multiple fracturing data and induced fractures from image logs. A solution can be obtained with a minimum of two data sets. However, using an inversion technique, a solution can be obtained with any number of data sets, a
12、s the solution is over determined. A fundamental understanding of fracture initiation in arbitrarily inclined wellbores under various in situ initial stress conditions is essential for the efcient and effective design of hydraulic fracture systems. The basic equations describing the stress distribut
13、ion around a horizontal, vertical and inclined wellbore may be derived from the solutions developed by Kirsch 11, Fairhurst 12 and Bradley 13, respectively. It is general believed that a fracture initiates when the maximum tensilestress induced at any point around the wellbore exceeds the tensile st
14、rength of the formation at that point. When this occurs, the resulting fracture on the wellbore wall will have an orientation that is perpendicular to the direction of the most tensile principal stress. The angle between the wellbore generatrix and the fracture orientation on the wellbore wall is ca
15、lled the trace angle (e.g., 1417), which can be observed by high-resolution electrical imaging technologies (e.g., 18). Someprevious attempts have been made to use the fracture trace angle to determine in situ stresses (e.g. 10,16). This paper presents a new method for determining the in situ stress
16、 state from hydraulic fracturing data. It is shown that an analytical solution can be obtained when fracture trace angle is available. Later in the paper, this new method is applied to data from the Kuparuk River eld in Alaska as reported in Ref. 1, and shown to predict in-situ stresses in good agreement with eld data. When fracture trace angles are not available, other incomplete inversion methods canbe used, such
