Abstract

Creating a gas gathering system model that is capable of accurately reproducing current rates and backpressures, as well as being able to predict future operating conditions after adding new wells, installation of a loop or booster compression can be a challenge. It does not need to be difficult though, as long as the modeler takes a comprehensive, logical approach. The approach required begins with three overriding rules:

  1. break the problem into manageable pieces,

  2. select an appropriate pressure loss correlation and trust it without utilizing any adjustment factors, and

  3. always conduct a field trip to resolve differences between measured and calculated pipeline pressure losses.

The objective of this paper is to present the modeling approach developed and utilized by our pipeline modeling group called the "Five Step Modeling Method"1. This is the first of several papers that will describe in detail, with cases studies, each of the modeling steps;

  1. Pipeline Pressure Loss Match,

  2. Well Deliverability Match,

  3. Compressor Capacity Match,

  4. Base Case, and

  5. Production History to Forecast Match.

This paper presents the Pipeline Pressure Loss Match.

Introduction

This paper is based on a gas gathering system operated by a Canadian company in Central Alberta. Currently, natural gas from a total of 16 wells is produced to a compressor station and then sent to sales. The purpose of the model is to simulate the effect of the tie-in of a number of low-pressure wells. Since the construction of the pipeline links portion of model is largely a mechanical operation, discussion will focus on the process of gathering, interpreting and utilizing field performance data to match measured pressure losses to modeled pressure losses.

Application of the pipeline pressure loss match begins with the gathering of performance data and selection of a match point. Most gas gathering systems are run in a constant state of flux; wells are produced intermittently, facilities temporarily go offline for a variety of reasons, gas is diverted to another system or compressor, and new wells or facilities are added. Consequently, it is very difficult to match systems over extended periods of time and so most models are matched at a point in time. Once the match point has been selected, the performance data is compared to the model calculated data. The key from this point onward is to highlight the differences between the measured and calculated data and gather additional data to resolve those differences. Experience has taught us that the differences are usually not deficiencies in the model but rather unknown factors in the field. As a result, field trips have become an integral part of the modeling matching process.

Performance Data

The performance data required to match a model to current operating conditions are (1) the wellhead and line pressures plus the current flowrate (gas and liquid) for each well, (2) suction and discharge pressures plus throughput at each compressor. This information is typically gathered on at least a daily basis and is generally readily available.

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