Monte Carlo Simulation Of Offshore Terminal Operations
Authors: Orkin Gary L. , Folck Richard L. , Startzman Richard A. 
Published: December 2007

This paper discusses the use of Monte Carlo Simulation in the study of offshore terminal operations. It describes the assumptions, types of input data required, and results of a computer program that mathematically reproduces the step-by-step, day-by-day operations of tanker loading in environmentally hostile offshore areas.

The data and results of a sample study are presented to show how such a program can be used in presented to show how such a program can be used in offshore terminal design.

Introduction

Offshore loading systems are attractive alternatives to pipelines for producing oil from fields in environmentally hostile areas. Their use is increasing throughout the world for many reasons. Same of these are:Early ProductionShipments can start by tanker while a pipeline is being built. A good example of this is Phillips' North Sea Ekofisk field.Pipeline Too CostlyThis occurs where the distances are great, the water is very deep, and/or the pipe laying costs are high due to severe weather. An example is Mobil's Beryl field in the North Sea.Small FieldsThese fields may not be able to justify the investment in a pipeline. Tanker loading, with its lower initial costs will make some fields economic. Hamilton Brothers' Argyll field in the North Sea is a prime example. This third use of offshore tanker loading has a very promising future.

But there are problems when tankers are loaded on the high seas. The main one is that during bad weather the tankers will not be able to berth at the terminal and must wait until the weather improves. This means that a field may be shut-in during poor weather, lowering the throughput efficiency (amount of crude loaded as a percent of field production potential). For high potential fields the cost of lowering the throughput potential fields the cost of lowering the throughput efficiency by only 1% could be very great. The sample problem described in this paper has a field producing problem described in this paper has a field producing 100,000 B/D. A 1% loss at $12.00/bbl. will cost $12,000/day or $4,380,000/year. This creates sizable incentives to increase throughput.

There, are three main ways to increase the throughput efficiency of the terminal. The first is to provide enough storage so that the field doesn't have to provide enough storage so that the field doesn't have to be shut-in during at least part of a bad weather period or when a tanker is not available for loading. But offshore storage is very expensive. Its cost must be offset with increased field production.

The second method is to provide more sophisticated loading system to allow berthing and continued loading in very bad sea conditions. Systems are now in operation that allow loading in up to 30-foot seas. This would substantially reduce weather downtime. However, the cost of this 30-foot capability is in the $30,000,000 range as opposed to $10,000,000 for a system to load in calmer (15-foot seas) conditions. Again, a balance would have to be achieved between costs and benefits.

The third method is to provide the proper number of correctly sized ships in a dedicated tanker fleet. In general, some excess tanker capacity is needed to avoid shutting in the field during bad weather conditions either at the field or between the field and the delivery port. Also, these tankers will have to be modified in most cases for bow loading and automatic connection and disconnection of loading and mooring lines. Also, the ships would require slow astern capability and may be bow thrusters.