Structural Improvement of Differential Motion Assembly in In Situ Pressure-Preserved Coring System Using CFD Simulation

Abstract

In situ pressure-preserved coring (IPP-Coring) is one of the most efficient methods for identifying the scale of the oil and gas content. However, the differential motion assembly of the IPP-Coring system often undergoes ball and ball seat seal failure and sticking due to surface erosion, and a greater pressure drop may unexpectedly trigger the assembly. This paper addresses these issues by improving the hydraulic structure of an assembly based on a deep understanding of the flow characteristics in the assembly, thus increasing the success rate of the IPP-Coring. Computational fluid dynamics (CFD) was employed to investigate flows in a differential motion assembly. The effects of the diameter and outlet structure of the ball seat on the fluid status, velocity, and pressure distribution were thoroughly analyzed. When the ball seat diameter increased from 30 to 40 mm, the maximum velocity and pressure drop decreased to 0.55 and 0.2 times their original values, respectively. There was a severe vortex area in the differential motion assembly due to the presence of the ball seat, but changing the outlet structure in the ball seat to an arc structure decreased the length of the vortex area and the fluid velocity near the wall to 0.7 and 0.4 times, respectively, compared with those with the original right-angled structure. In addition, the pressure drop decreased to 0.33 times the original value. Thus, the hydraulic structure of the assembly was improved, and a 40 mm diameter ball seat and an arc-shaped ball seat outlet were selected. Particle trajectory and erosion calculation results showed that the improved structure has a lower particle velocity and less impact on the wall, and the average erosion rate is only 0.42 times the value of the original structure. Due to the better erosion resistance and smaller pressure drop, the improved structure shows promise for field performance.

Structural Design and Numerical Analysis of an All-Metal Screw Motor for Drilling Applications in High-Temperature and High-Pressure Environments in Ultra-Deep Wells

“…The mineral resources in the shallow part of the Earth have been gradually depleted, and at present, resource development is continuously moving to deeper parts of the Earth [1,2].With continuous research on the development of unconventional oil and gas resources such as shale gas and shale oil in China [3,4], there has been unprecedented development of drilling projects deep underground, which are the most direct way to obtain information about the deep part of the Earth [5,6]. It is now generally accepted that scientific drilling in mainland China should target extraordinarily deep wells from 9000 to 15,000 m in depth [7].…”