| Downhole tubing is the main component of oil well and gas well,the cost is about 20%～30%of the whole cost of development and exploration of wells.The oil casing is a permanent part of the oil well and gas well,generally accounting for 73%～76%of the entire consumption of downhole tubing material.It can be said that the service life of oil well and gas well depends on the life of oil casing.During the process of the exploration of high sulfur oil(gas)field,sour gas of underground is fatal to the corrosion of oil casing.With the vigorous development of oil and gas industry in China,it is imperative for the exploration and development of high sulfur gas field,and the contradiction between the security and economy of downhole tubing is growing.At present,there’s a marine gas reservoir in a high sulfur gas field in Sichuan basin waiting for exploring.This reservoir possessed following characteristic:high content of hydrogen sulfide,medium content of carbon dioxide,ultra deeply buried,high temperature.In this reservoir,the content of H2S is 5.14%on average,the content C02 is 7.5%on average,the formation pressure is 66.33 69.23 MPa,the formation temperature is 149.5 to 157.414 ℃,the buried depth is deeper than 7000 m.As we can see,this reservoir is equipped with following problems:high pressure of gas reservoir,ultra deeply buried,severe corrosion and complex condition and so on.This has brought a huge challenge for economically and safely exploring the gas field.In order to solve the above problems,this paper based on the in-depth research of the selection status of well completion string material in high sour gas field at home and abroad,through the analysis of the corrosion environment,and connecting with the requirement and method of material selection surrounding by containing hydrogen sulfide environment,determines the environment and materials of the corrosion evaluation test of the material selection of the completion tubing of in Changxing group gas reservoir in Sichuan certain gas field.The experimental results under the simulation environment of corrosion show that:Under two indoor simulated conditions,the uniform corrosion rate of domestic nickel-base alloy is below 0.025 mm/a,accordingly,domestic nickel base alloy can completely meet the requirement of the uniform corrosion of marine gas reservoir in Sichuan high sulfur gas fields.All domestic nickel base alloy material sample sulfide stress resistance are good,neither sulfide stress corrosion cracking.Through domestic nickel base alloy material with high sulfate-resistant casing of galvanic corrosion study shows that the nickel base alloy after connected to 718,110 ss,in a certain environment,four kinds of galvanic corrosion rate of nickel base alloy compared with single bolt corrosion rate is reduced,but the 110 ss material galvanic corrosion rate with single coupon corrosion rate increased a lot,while in nickel base alloy and the combination of material 718 cases,when the load stress level is bigger,the corrosion rate of nickel base alloy specimen is far less than the corrosion rate of stress level is lesser.A Marine gas reservoir of high sulfur gas field in sichuan corrosion condition,the experiment used the 4 c,4 d nickel-based alloy material oil casing and downhole tool can meet the requirements of corrosion resistant material 718.Finally,combining with the completion of similar gas reservoir material selection,and to consider economy,selected for a high sour gas fields in sichuan changxing group gas reservoir selection plan:1)Oil layer casing:well depth above 4000 m tubing chosen 4 c or less nickel base alloy,well depth 4000 m tubing or choose domestic 4 d class nickel base alloy;2)All tubing choose 4 c nickel-based alloy tubing;3)Tool to select 718 material. |
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