Your fellow subsea engineer finally returns from honeymoon dive trip, all tan an

Question

Your fellow subsea engineer finally returns from honeymoon dive trip, all tan and rested, talking incessantly about how great it was, etc. etc. While everyone is getting back up to speed on the subsea equipment delivery status, drilling results and recent developments, you spent all week and the weekend churning through subsea development options and issues for these new oil reservoirs discovered in your project’s development well pre-drilling. And your company reservoir engineers and geologists are all saying its looking more and more like they will have the best well trajectory and reservoir penetration by drilling these new reservoirs from a surface location about 3 miles to the southwest of where your wells are located (just confirming – these are directionally drilled from 3 miles away?).

Fluid sample data is not yet available (sent from rig to the lab), but unofficially you were told they looked like they were contaminated with drilling mud. No water samples were taken, no cores either. One of the oil zones looked very clean, but it was unclear how big the reservoir was at the location where it would be penetrated. Given the preliminary geologic mapping, there was some debate as the whether there was an oil water contact seen on the log.

Question 1: What are the important system level flow assurance issues that need to be assessed, if these new reservoirs are going to be drilled 3 miles away from the tie-in point to the existing gas system?

Question 2: In the architecture, will the oil be tied-in to the existing gas system? If so, what flow assurance issues can arise due to the fluids mixing?

Explanation / Answer

Ans:

Question 1 answer:

Maintenance and production stop is a critical issue due to loss of cash flow and expensiveoperations. When flowing reservoir fluids over a distance, several flow assurance issues musttherefore be addressed to ensure efficient and continuous flow. Since no fluid samples areavailable, all issues must be thought of and a contingency plan must be in place.

Thermodynamics:  To avoid precipitation of unwanted substances, a solid plan to keep the flow with high enoughtemperature is important. This can be addressed through isolation of pipelines, electrical heating,etc.

Pressures:  Excessive pressure drops over chokes, bends and rough pipes will increase the chance of flowassurance issues. To address these issue, the flow should be efficient.

Fluid Flw patterns:  

A steady flow can be uniform or non-uniform and similarly an unsteady flow can also be uniform or non-uniform. For a steady flow discharge is constant with time and for a uniform flow the area of cross section of the fluid flow is constant through the flow path.

Examples of Different Flow Types

Steady and Uniform Flow: Flow through a pipeline of constant diameter with a discharge constant with time.

Steady and Non-Uniform Flow: Fixed discharge flow through a tapering pipe. Water flow through a river with a constant discharge is also a good example of such flow as the span of river generally varies with distance and amount of water flow in river is constant.

Unsteady and Uniform Flow: A flow through pipeline of constant cross section with sudden changes in fluid discharge or pressure.

Unsteady and Non-Uniform Flow: Pressure surges in a flow through a pipe of variable cross section. A practical example can be the water flow in the network of canals during water release.

Question 2 answer :

In the architecture, Yes the oil will be tied-in to the existing gas system because fluid composition can be modified to meet these challenges. One option is to separate oil and water from gas by subsea processing at low pressure in which case fluid can circulate at a temperature below that of hydrate formation.

The separator can be located at the riser base or the wellhead, depending on the pressures available, the tieback length, and slope. The goal is to mitigate the hydrate risk after the separation, to remove gas so as to reduce heat losses, and to achieve efficient liquid boosting.

Flow assurance focuses on three main aspects:

1. Avoid flow restrictions (excessive pressure drop, blockage or intermittent production).

2. Safeguard the structural integrity of parts of the production system from damages caused by internal flow.

3. Maintain the functionality and operability of components in the production system.

There are multiple issues that are typically addressed in flow assurance:

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.