Structural Simulation for Oil and Gas Products

The design of oil and gas products presents many unique challenges. The first step for designers and engineers is to understand how an oil well works and how it is composed. In the figure below is a regular oil well. The casing is in contact with the soil, and as a result, it is generally under external pressure. The tubing is in charge of conducting the fluid, so it can be under different type of loads such as internal and external pressure, tension and compression.

Inside the tubing we have the sucker rod, which is used to activate the pump in the bottom of the oil well. A regular oil well is between 1500 m to 5000 m, depending upon the exploration region. There are many connections in one single string, therefore, if only one of these connections fail, the whole oil well stops producing.

Oil Wells

There are many types of oil and gas products, in this article I will focus on a couple of them: sucker rod and threaded tubing-casing connections. These components present different failures in the oil well that causes production problems and can lead to higher costs. In the figure below we have a sucker rod connection (left) and tubing-casing connection (right).

Sucker Rod and Threaded Connections

Regarding the simulation of these components, it is very important to know the failure process of each of them. In the case of sucker rods there are alternating loads that transmit a variable stress field. Also stress concentrations are seen in the thread roots. These stress effects tend to produce fatigue failure after a certain number of cycles.

The figure below shows a sucker rod connection that failed in the last engaged root thread. The picture on the left shows the failure point, while the picture on the right shows the failure process starting with a ductile failure until the whole section collapses showing a fragile fracture. The picture at the bottom shows a complete connection and an initiated fracture on the pin component.

Fatigue Failure in Sucker Rods

Threaded tubing-casing connections show a different failure mode. Because they are under different types of static loads (tension, compression, internal pressure and external pressure), a permanent deformation appears due to material plasticity. Finally, the problem in the connection is the leakage presented in the seal area.

Permanent Deformation Failure

SOLIDWORKS Simulation Solution

These failure modes on sucker rods and tubing-casing connections lead to higher cost and longer development time. To avoid these problems, it is necessary to use software that enables you to test different design options; evaluate product performance; is intuitive and easy to use; and offers ongoing support.

SOLIDWORKS Platform Key Characteristics

The solution for fatigue failure in Sucker Rods was to redesign the connection using stress concentration factors to achieve the optimal design. The figure below on the left shows the result for the regular API design (Option 1) and a new modified API design (Option 2). The modified design only has a shoulder angle modification that distributes the stress field in a better way compared with the regular design. On the right we have a stress coefficient comparison. The regular design shows the worst values (lower red curve) and the new design definitely show better stress coefficient (upper green curve).

Sucker Rod Results

Regarding threaded connection, the Connection Seal Performance was evaluated, allowing the designer to define the critical loads. In the picture below I show the seal area (left) and the seal performance evaluation (right). I usually use three types of factors: 1) SF – seal force; 2) SP – seal peak; and 3) SL – seal length. These factors allowed me to evaluate the seal performance.

Threaded Connection Results

As a summary of the study of these two cases, we can arrive to the following conclusions:

Flexible Simulation Tools for choosing the best design shortens the development time
Evaluation of component performance (Casing, Tubing) results in higher-quality products

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