Research Wells Overflow Rule

The key point of well control is to prevent overflow and blowout. Overflow would not be a terrible thing, as long as some right measures have been taken. The process from overflow to blowout is gradual, no matter reservoir, water layer or gas reservoir. So understanding the overflow law is helpful to adopt the right control measures to eliminate the potential dangers and ensure the safety of drilling.This paper established the seepage models about influx, conducting experiments in the laboratory. According to the migration process of fluid within the wellbore, multiphase flow equations were established, which are mainly composed of each phase continuity equation and momentum equation. With the numerical analysis method (the finite difference method was used in this paper), the established models were quantized and solved. The occurrence and development process about overflow were simulated by computer. The analysises shew that the overflow occurrence and development process was not only affected by the drilling parameters (penetration rate, displacement, etc.), but also closely related to the specific reservoir and the properties of the liquid in the reservoir.According to the basic theory of heat transfer and thermodynamics, temperature distribution model was established to forecast the wellbore temperature. And annulus pressure prediction model was established, which might predict the annulus pressure distribution in the wellbore. The supercritical fluid phase transformation after the overflow was forecasted, using the wellbore temperature and pressure prediction model. Additionally calculation model of gas solubility in mud was established to analyse the law of gas solubility in the mud.According to the theoretical model, the software analyzing the rule of oil and gas wells overflow was developed. With the help of the software, we could simulate the overflow dynamic process, calculate temperature and pressure distribution in the wellbore before and after gas cut, and analyze the gas solubility in the wellbore and the rule of phase transition of critical fluid.In this paper, the description in detail and comparative analysis about the occurrence and development process of the overflow, the main factors influencing the process and the properties of fluid after overflow were made, providing a guiding for understanding the overflow and well killing operating.