The Study Of Formation Stress And Its Application In The Zhenjing Oil Field

The reservoir of Zhenjing oil field are mainly Yanchang group of Mesozoic, which is blong to structural-lithological reservoir. The pore structure of the reservoir is very complex and with strong heterogeneity. It is a typical reservoir with low porosity, low permeability and low pressure. The anomaly of formation stress and pressure can bring great disadvantage to drilling, cementation, fracturing and other projects.Stress magnitude, stress direction, stress distribution and the evolutionary history of stress field are the main content of formation stress research in oil and gas exploration and development. Stress field evolution not only to control the formation and distribution of oil and gas basins in the basin structure, but also effect the development of oil source, reservoir and caprock strata, and hydrocarbon generation, migration, accumulation process.In the evolution of stress, stress changes and internal geological force changes can lead eventually to the formation of geological faults and fractures, which provides a channel for the oil and gas migration.In recent years, in order to achieve a breakthrough in Zhenjing oil field, North China Petroleum Bureau of China Petrochemical Group have laid a large number of horizontal wells. Horizontal wells stability and productivity can be affected considerably by geostress. while perforating and fracturing also need the information of geostress and formation pressure. There is an urgent need to carry out research work in terms of stress and formation pressure, providing an important reference for drilling, perforating, fracturing and other projects.Therefore, the calculation of rock mechanics parameters, establishement of stress calculation model, establishement of stress profiles, wellbore stability evaluation, determination of the direction of stress, study of stress distribution law, fracture identification and research of fracture distribution law, etc. have important guiding significance for drilling, completion and development of oil and gas field.This paper is mainly for low pressure, low porosity and low permeability tight sandstone reservoirs of Yanchang group in Zhenjing oilfield, study of the conversion model of static and dynamic mechanical parameters, stablishment of mechanical parameter profiles, analysis of the mechanical parameters features of different stratigraphic,calculation of earth stress, definitely stress direction, calculation of collapse pressure and burst pressure, wellbore stability evaluation, and providing important reference for drilling, perforating, fracturing and other projects.The main research contents are as follows:1.The conversion model of static and dynamic mechanical parameters have been established by measuring core mechanical parameters.The mechanical parameters of20cores in Zhenjing oil field were measured by triaxial rock mechanics experimental system. The rock mechanics parameters of cores compared with the parameters calculated by using acoustic wave (P-wave, S-wave) and density logging data. The conversion models of static and dynamic mechanical parameters have been established.2. Establishment of stress computing model for suitable to Zhenjing oilfield; The stress computing model for suitable to Zhenjing oilfield have been established by using hydraulic fracturing,logging data and other information (horizontal maximum and minimum principal stresses and vertical stress).3. Study situ stress field direction in Zhenjing oilfield;The situ stress directions in Yanchang group of Zhenjing oilfield have been determined by using core analysis testing and logging data (sound, electric dipole shear wave imaging logging). The stress profiles of each segment in Yanchang group have been established.4. Establishment of the computing model of formation fracture pressure and formation collapse pressure for suitable to Zhenjing oil field and calculation of the drilling fluid density window for maintaining wellbore stability.5. Calculation and application analysis of core mechanical parameters;6. Identification of tight sandstone fractures, study of the relationship between stress distribution and fracture distribution.The main innovations of the study are as follows:1. The conversion models of dynamic and static mechanical parameters in Zhenjing oil field have been established by using triaxial rock mechanics experiments, the mechanical parameters characteristics of different formations of Zhenjing oilfield have been statistical analysis.2. The situ stress model in Zhenjing oilfield have been established by combining hydraulic fracturing,logging data and other information (horizontal maximum and minimum stress, vertical stress, fracture pressure, formation collapse pressure, etc.), the drilling fluid density window of maintaining wellbore stability have been calculated.3. The geological understandings have been gotten through stress and cracks analyzes, these understandings have significances for exploration and development of Zhenjing oilfield, stress study.