| This paper was prepared for Petrochemical of China LTD's pilot project: Investigation of Fracturing Technology in Complex Situation in Baolang Oil Field . Exploration and development history show low reservoir permeability, intense water sensitivity, coal layer growing in oil formation or above and below oil formation and high fracturing working pressure in Baolang oil field, it is different from other low permeability oil field and shows special technological difficult point and is very complex oil field. Based on extensively investigation and research of literature, Baolang oil field earth stress analysis, rock mechanics performance measurement. Baolang oil field reservoir's major feature and perforated well stress analysis, this paper analyzed the reason of abnormal fracture pressure in waterfrac operating and presented method of predicting fracture pressure and technological measurement of reducing fracture pressure and analyzed quantitatively all method's effect. This can direct not only efficient development of Baolang oil field but development of other region with high abnormal fracture pressure. This paper presented:(1) Based on the core differential strain analysis and interpretation of logs and fracture working pressure, earth stress in Baobei block and Baozhong block is analyzed and the friction drag of fracture fluid is explained. The results indicate that earth stress and friction drag of fracture fluid are high in Baolang oil field.(2) The elastic modulus and poisson's ratio of rocks in Baobei block and restraining barrier (mud shale, coal layer) in Baozhong block are measured under the condition of simulation of Baolang oil field's earth stress (confine pressure 50 Mpa) . In the main, low rock's elastic modulus indicates intense reservoir plastic feature in Baolang oil field. The results of rock-breaking experiments under condition of triaxial stress show that fracture pressure of core samples is very high and beyond 80Mpa, the breakdown of granule roundstone's core of well B2219 is not apparent and major fracture is not observed. These results are identical with pressure operating curve.(3) Based on the analysis of rock composition feature, deposition feature and structural feature in Baolang oil field, tectonic action and anomaly transportation and rapid accumulation of sedimentary derivation and intense rock heterogeneity are regarded as the reason that result in abnormal fracture pressure. In Baozhong block, earth stress and fracture pressure are higher because of more intense tectonic action and lower reservoir permeability and lower compositional maturity and more intense compaction degree . In addition, heavy reservoir damage and high friction drag of fracture fluid in Baozhong block are also important and external cause that result in abnormal fracture pressure in Baolang oil field.(4) The CAD/CAE/CAM software Pro/Engineer (Pro/E) finite element analysis program on workstation are used to calculated the effect of stress distribution near perforating tunnel, which are caused by perforating parameter and low stress, it shows that big aperture and deep penetrating parameter can reduce fracture pressure, do not affect casing strength.(5) The cause of abnormal fracture pressure is diverse in waterfrac of Baolang oil field .It is related to perforating parameter and damage of working fluid to reservoir and high fluidfriction drag caused by bad fracture fluid, but preliminary affecting factors are such geofactor as deposition feature, structural feature and rock structure. This paper presented technological measure to reduce breakdown pressure, it includes high energy gas fracture preliminary processing and acidizing preliminary processing and optimized perforating parameter at the basis of optimized fracture fluid performance.(6) According to kinetic process of high energy gas fracture , rock-breaking function was explained . The degree that high energy gas fracture reduce fracture pressure was determined quantitatively, according to the strength theory and failure mechanism of rock mechanics.(7) Ba...
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