Study On Safety Pressure Control Of Natural Gas Overflow

In dealing with overflow in well, the casing pressure in the condition of shut in well is an important safety decision criteria:When casing pressure exceeds the criterion, it will damage the well control equipment, brake through the casing in well, press and leak the weak formation, and cause variety of accident; Only the value of casing pressure is less than criteria of safety pressure, killing wells and processing the overflow can be ensure safely.According to the national and industry standards and provisions of oil field company, in the implementation of the method of determination of reasonable shut-in casing pressure, there are the following questions:The regulation of determine the biggest shut-in casing pressure which is restricted by the collapse pressure of weak formation near the casing drive shoe, it does not relate to the difference between the overflow condition and leak off test conditions; According to the regulation of determine the shut-in casing pressure by 80% value of internal pressure resistance strength of casing, it does not relate to the wear of casing; It is need to choose appropriate shut-in well method, on account of the water hammer effect by shut-in well.The purpose of this paper is to study how to determine the safety shut-in pressure which is credible and consistent with the field practice, to determine the supplementary measure for casing pressures exceeding criteria in killing well, to provide a good foundation for processing natural gas overflow.By establishment the mathematical model, comparison and analysis, research on water hammer pressure effects of wellhead, research on the reasonable shut-in casing pressure in consideration of the difference between the overflow condition and leak off test conditions. Using the ANSYS software, the residual internal pressure strength of casing can be determined by finite element analysis. The following conclusions eventually can be get:The wellhead device is required to reach the required pressure level, installed and tested according to industry standards requiring; Water hammer pressure generally does not exceed the bearing resistance of wellhead device, hard shut-in is safe for control overflow when gas invasion and overflow.The internal pressure strength of casing will decreases after it worn, it may be pressed broken while killing well. Application the forecasting and detection method of internal pressure strength of casing wear, it is easy to forecast the wearing condition of casing and revise the actual wearing condition of casing. It is not only useful to determine the safe shut-in pressure,but also provide the reliable basis for application higher strength of the casing advance.Killing well while gas invasion, gas expansion results in high casing pressure. According to the casing pressure of certain well which is killing well, judge whether the formation near the casing shoe will leak by high pressure, when the casing pressure of certain well exceed the biggest value which is determined by detection of formation breakdown pressure. When casing pressure exceed the safe value, blowing off the mud to make wellhead device decompress, casing withdrawal to enhance the internal resistance strength of wellhead or efficient killing well method which can decrease choke casing pressure, etc. shall be used to provide security for the follow-up operations, according to different conditions.