The Study On The In-situ Stress Regime And Its Influencing Factors In The Low-permeability Block 5 Of Bonan Oilfield

The Block 5 of Bonan Oilfield, the study area of this research, resides at the southeast side of the oilfield. Through years of development, the reservoir shows increasingly serious areal and cross-layer flooding problems, which heavily affects future recovery efficiency. In order to future tap the reservoir potential, the oil-bearing formations need to be fractured and the well pattern to be adjusted. This study on in-situ stresses distribution and influencing factors bears significance on guiding the fracturing operations and adjustment of well pattern. The results of this study are listed below.The poroelasticity theory is used, which was first founded by Maurice A. Biot, as the theoretical framework of the numerical simulation experiment. The mathematical simulation model was established and geological models were built using FLAC3 D. Several FISH programs were written to assist the analysis and plotting.The in-situ stresses distribution of both the well-group area is modeled. Within Y5-22 well group area, the influence the dynamic production had on the stress regime mitigates as the injection-production activity becomes less intensified. When Y5-21 turned to be an injection well after years of production, its effect on the surrounding formations reversed. However, the influencing radius is within the well distance. The value of hσ relates to sandstone-mudstone boundary closely and varies little within the mudstone area. In Y65-1 well group, as well production and injection intensifies, the hσ value and direction variation increases. When the only injection was shut down; the absolute value of hσ within this well group decreases compared the initial value. Through the whole production history, the hσ variation of Group Y65-1 is less severe compared to that of Group Y5-22.Static factors affecting the in-situ stresses were investigated. Young’s modulus has little effect on the direction change of hσ, which is also true for Passion’s ratio. However, the Biot coefficient has a huge influence both on the value and direction variation of hσ.Dynamic factors were also studied. For one single production well, the hσ values of same locations of different models decrease and their direction variation rises as the models’ flowing bottomhole pressure decreases(or the production rate increase). Similarly, as the injection pressure or injection daily rate rises, the change of hσ intensifies. However, more wells in the model will cause larger direction change in certain areas within the model.Well pattern’s influence on the stress regime has also been investigated. For the five-spot injection pattern, the variation of the stress regime is related to the production-injection intensity of this well group. Under same production circumstances, the direction change of hσ detected is less severe than that of the well pattern with one injection well and two production wells, which indicates that the direction change of hσ is not a simple add-up of influence from injection and production wells.