Mechanical Detection System for Injection Production String in Oil and Gas Wells With High Temperature and High Pressure

The research on the injection production string (IPS) system mechanics was limited to theoretical derivation and numerical simulation due to the lack of a mechanical detection system (MDS) for IPS. This made it difficult to further optimize string design and reduce accidents during injection and production operations. The three-dimensional (3-D) equivalent axial force model (3-D EAF model) of IPS was established using the 3-D vector method, and MDS based on the 3-D EAF model was designed. The calculation and detection of the DXX-162-X20 example of the Shengli Oilfield well showed that both the 3-D EAF model and MDS met the actual working conditions of IPS. The root-mean-square error between the calculated value of the 3-D EAF model and the downhole-measured data was less than 6.25 kN. MDS met the mechanical detection requirements under the injection production operation environment, such as a well-depth of 3000 m, well fluid pressure of 30 MPa, and downhole temperature of 80 °C. The MDS effectively detected the axial force of 0–300 kN using the strain gauge matrix detection method, and the standard deviation was less than 3.13 kN during each experimental point. The 3-D EAF model was used in more wells of the Bohai oilfield in China to predict the axial force in the process of IPS running down. The relative error was no more than 5%. The above results showed that the 3-D EAF model and MDS could effectively solve the mechanical detection problems of IPS in oil and gas wells having high temperature and high pressure and provided a theoretical basis and method support for the research of string mechanics.

I. Introduction

Injection production string (IPS) serves as an important link for transmitting energy and information between the ground and underground and plays an important role in layered water injection, layered gas injection, CO₂ injection, and production [1], [2], [3], [4], [5], [6]. The axial force of IPS changes greatly due to high pressure, high corrosion, and large fluctuation of parameters, such as temperature and pressure difference between the inside and outside of the string along the borehole direction. When the force exceeds the maximum static friction between the rubber barrel and casing or the tensile limit of IPS, accidents during injection production, such as packer sealing failure and tubing string fracture, will occur [7], [8].