Abstract
During deep-water gas wells testing period, predicting the generating zone of hydrate precisely in the whole flow range (bore holes and surface flow lines) is the key prerequisite of guarantee for testing flow. The unusual deep-water environment and low gas density make it easy to meet the conditions of hydrate generation during deep-water gas wells testing period, such as low temperature and high pressure, especially under the testing conditions, for instance, near mud line, surface chock line, low gas generating rate and surface shut-in. Wherefore, in view of all the operational modes during testing period (clean-out, variable rate flow, downhole and surface shut-in), based on temperature field of the whole flow range and phase equilibrium condition of hydrate, predicting method of hydrate generation zone is published; by taking enthalpy as the object of study, temperature calculation model increases the accuracy of temperature prediction; by integration of bore holes and surface lines, predicting plate of hydrate generation in the whole flow range is published. During flow period, the generating condition of hydrate is affected by rate of flow, and the lower the rate of flow is, the wider the hydrate generation zone is; during the stage of shut-in and initial flow, if pressure of strings is higher and temperature is lower, risk of hydrate generation will be greater and hydrate generation zone will be larger, so relevant actions should be taken to restrain hydrate generation.
Highlights
The unusual deep-water environment and low gas density make it easy to meet the conditions of hydrate generation during deepwater gas wells testing period, such as low temperature and high pressure, especially under the testing conditions, for instance, near mud line, surface chock line, low gas generating rate and surface shut-in
In view of all the operational modes during testing period, based on temperature field of the whole flow range and phase equilibrium condition of hydrate, predicting method of hydrate generation zone is published; by taking enthalpy as the object of study, temperature calculation model increases the accuracy of temperature prediction; by integration of bore holes and surface lines, predicting plate of hydrate generation in the whole flow range is published
During deep-water testing period, prediction of hydrate generation zone is the prerequisite of prevention for hydrate and flow guarantee for the whole flow range [1]-[3], and three aspects are needed: 1) prediction of temperature and pressure—we start study
Summary
During deep-water testing period, prediction of hydrate generation zone is the prerequisite of prevention for hydrate and flow guarantee for the whole flow range [1]-[3], and three aspects are needed: 1) prediction of temperature and pressure—we start study. Based on the theoretical analysis, combined with specific conditions of deep-water gas wells test during different period, computing method for pressure and temperature of strings has been proposed and used to analyze the potential zone of hydrate generation under the circumstances, flow test, downhole and surface shut-in, and initial well startup by combining conditions of phase equilibrium. Taking factors which affect temperature distribution in bore holes into comprehensive consideration, including environmental temperature, wellbore structure, structure of testing strings, job condition and formation fluid property, traditional method only based on heat transmission is changed, considering choking effect and work by volume change during flow behavior of high speed gas, and taking enthalpy of compactible gas during flow behavior as subject in the study, temperature field equation of bore holes for deep-water wells during testing progress is established. In the formula: V—specific volume, m3/kg; T0 —temperature of triple point, K; p0 —pressure of triple point, MPa; Cp —heat absorption capacity, J/(kg∙ ̊C); β—coefficient of thermal expansion, 1/ ̊C
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