Abstract
For the “three-high” gas wells in Sichuan Basin which are often regulated for production rate and shut-in for maintenance, annular pressure by temperature effect is a kind of wellbore safety threat that cannot be ignored. In this work, the wellbore temperature and pressure calculation model of gas–liquid two-phase flow with non-hydrocarbon correction and the prediction model of annular pressure by temperature effect is developed. Moreover, the judgment chart of annular pressure type is established through a large number of simulation calculations with different gas production rates and water production rates. Example calculation shows that whether water production and non-hydrocarbon components are considered in the prediction model has a non-negligible influence on calculation results. The predicted annular pressure is compared with that obtained from the actual measurement showing a good agreement. Meanwhile, the judgment chart realizes the valid determination of annular pressure type for three “three-high” gas wells in Sichuan Basin. Influential factors analysis indicates that reducing the thermal expansion coefficient of annulus fluid, adding the hollow glass spheres or injecting highly compressible protective liquid into the annulus and installing compressible foam material on the inner wall of casing are effective methods to control the annular pressure by temperature effect. To reserve partial annulus space can effectively reduce the annular pressure by temperature effect. For most of “three-high” gas wells in Sichuan Basin, the optimum height of annulus air cavity is 100 m.
Highlights
There are some marine carbonate gas fields in Sichuan Basin, including Puguang gas field, Yuanba gas field, Moxi gas field and so on. These gas fields are characterized by high pressure (HP), high temperature (HT), high hydrogen sulfide (HHS) content, complex geological condition, water production and densely populated area
According to the cause of production casing annular pressure, it can be divided into annular pressure caused by temperature effect and annular pressure caused by leakage effect
Abnormal annular buildup pressure is the biggest threat to production safety, but for these “three-high” gas wells in Sichuan Basin which are often regulated for production rate and shut-in for maintenance, annular pressure by temperature effect is a kind of wellbore safety threat that cannot be ignored (Singh et al 2012; Julian et al 2007)
Summary
D Diameter of wellbore,m Rem Reynolds number, dimensionless Tf Fluid temperature in tubing, °C q Radial heat loss of fluid, J/s cpm Specific heat at constant pressure of fluid, J/(kg·°C) H Joule–Thomson coefficient, °C/Pa rto Tubing outer diameter, m Uto Total heat transfer coefficient, W·(m·oC)−1 ke Heat transfer coefficient of formation, W·(m·oC)−1 Gt Mass flow rate of gas–liquid mixture, kg/s f (tD) Dimensionless time function, dimensionless Te Formation temperature, oC Uta Annulus heat transfer coefficient, W·(m·oC)−1 rh Wellbore radius, m rco Casing outer diameter, m hr Radiative coefficient of annulus fluid, W·(m2·oC)−1 hc Convective heat transfer coefficient of annulus fluid, W·(m2·oC)−1 Kcem Heat transfer coefficient of cement ring, W·(m·oC)−1 Th Temperature at the outer edge of cement ring, oC Ta Temperature in production casing annulus, oC Δpa Annulus pressure change value, MPa l Thermal expansion coefficient of annulus fluid, oC−1. ΔTa Annulus temperature change value, oC ΔVa Annulus volume change value, m3 Va Annulus volume, m3 Ctot Deformation coefficient of tubing and casing, 10−6 MPa−1 s Thermal expansion coefficient of tubing and casing, 10−6oC−1 p1, p2 Pressure before and after annular pressure change, MPa z1, z2 Gas deviation coefficient before and after annular pressure change, MPa Ta1, Ta2 Annulus temperature before and after annular pressure change, oC Vg1, Vg2 Upper air cavity volume before and after annular pressure change, m3
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