Dynamic analysis of wellbore stress field and wellbore stability in carbonate reservoir production process
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Carbonate rocks usually need to be acidified to achieve transformation and increase production. However, the deep carbonate formation is complex, and the change law of mechanical parameters is not easy to grasp. After acidification, accidents such as borehole instability and sand production occur occasionally in the production process, thus damaging the reservoir and reducing the production. In this article, the downhole core of carbonate reservoir of Qixia formation in Sichuan province is taken as the research object, and rock samples with different time of acid soaking were tested by field acid solution. Based on the experimental data, software simulation is used to analyze the dynamic variation law of wellbore stress field and wellbore stability in the process of reservoir production after acidification. It also provides a theoretical basis for selecting a reasonable completion method. The experimental data show that the effect of acid erosion on porosity and permeability of carbonate rocks is more obvious than that of original rock samples, and the overall trend is increasing. Acidification has a significant impact on the rocks’ mechanical strength and elastic modulus which was reduced to the maximum extent after 4 h of acid immersion. Subsequently, the reduction of compressive strength and elastic modulus became smaller, and the overall change law of Poisson’s ratio was not obvious. The simulation analysis shows that during acidizing production, the pore pressure of wellbore is relieved, which is beneficial to the stability of wellbore, and the overall stability of the sidewall after acidizing corrosion showed an improving trend; it is considered that the borehole stability of Qixia formation meets the open-hole completion conditions of acidizing fracturing. However, after acidification of fractured rock samples in Qixia formation, the acidification further reduces rock mechanical properties and wellbore stability, which may lead to wellbore instability and sand production. The experimental data and numerical simulation obtained in this paper provide a certain theoretical basis for the design, simulation, and optimization of acid fracturing of Qixia formation reservoir.
KeywordsCarbonate rock Acidification Poroperm parameters Mechanical parameters Drawdown pressure Wellbore stress field Wellbore stability
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Conflict of interest
The authors declare that they have no competing interests.
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