PSI - Issue 16

Ihor Chudyk et al. / Procedia Structural Integrity 16 (2019) 260–264

261

Ihor Chudyk et al. / StructuralIntegrity Procedia 00 (2019) 000 – 000

2

capacitance characteristics of the bottomhole zone. There are various types of killing fluid depending on the main component. The most widely used are fluids based on inorganic salts. In order to increase production of hydrocarbons special attention is paid to the maximum removal of products from well, applying methods of intensifying the flow of hydrocarbons (Kondrat et al. (2014, 2017)). For this purpose acid treatment of wells are used, as a result of which aggressiveness of killing fluids increases and severe pitting corrosion takes place. Long-term exploitation of wells leads to degradation and wear of elements of the drill column, primarily drill pipes and their threaded joints, due to the interaction with formation water and drilling mud. The main causes of fracture of drill pipes and joints, revealed by failure analysis, are corrosion damages, corrosion fatigue failure and wash outs (Kryzhanivs’kyi e t al. (1991, 2014, 2015); Chernov et al. (2002); Lu et al. (2005); Fangpo et al. (2011); Zamani et al. (2016)). For hydrodynamic wells the process of gas hydrates formation, which intensifies internal corrosion (Obanijesu et al. (2011), Poberezhny et al. (2018)), can lead to increasing a failure risk and localization of corrosion processes (Maruschak et al. (2015); Yavorskyi et al. (2016); Poberezhny et al. (2017a)). This is also one of the main causes of erosion damaging in gathering pipelines (NACE Standard RP0775-2005). Therefore, corrosion damaging is one of the reasons of integrity violation of drill column (Poberezhny et al. (2017b). The article aim is to study the effect of the killing fluids on the corrosion rate and the lifetime of the drill pipe. 2. Materials and methods The objects of the study were the steel pipes of the G105 grade steel with a wall thickness of 9.19 mm, the chemical composition of which is given in Table 1. The physical and chemical analysis of two samples of killing fluids from the wells was carried out by the Laboratory of Corrosion-Mechanical Degradation of Materials and Structures of IFNTUOG with the equipment support of LLC Geosynthez Inzhenering (Table 2).

Table 1. Chemical composition of G105 drill pipe steel (wt ％ ). Component C Si Mn P S Cr

Mo

Ni

V

Ti

G105(1)

0.26 0.13 1.49 0.013 0.012

0.33

0.30

0.029 0.005

0.010

According to the results of chemical analysis it was determined that the main corrosive components in both studied fluids are chlorides, high concentrations of which can over time make the internal surfaces of pipelines and equipment to corrode. In addition, one of the studied fluids has a low pH, which further increases corrosivity of the medium.

Table 2. Physical and chemical parameters of killing fluids

Killing fluids KF1

Parameter

KF2 1190 3,57

Density, kg / m3

1090 7,22

рН

Са 2+ , mg / l Mg 2+ , mg / l

301

36230

–

–

Cl - , mg / l

60922

154425

- , mg / l 2- , mg / l 2- , mg / l

NO 3 SO 4 CO 3

–

1714

376

223

4

–

- , mg / l

HCO 3

1436

2520

Corrosion tests were performed in the killing fluids. Samples of 50  20  2 mm made of the G105 grade steel were tested. The studied samples were immersed in the test fluid in special cells and held in it for three days at a temperature of 150 °C. Corrosion rate of steel samples was evaluated using weight loss method (the decrease in