Abstract

The typical gas field aging signs are the production pressure decline and the increased reservoir water production. In these conditions, water accumulation may occur both in wells and in pipelines resulting in:

  • further reduction of gas production (in addition to depletion) due to static head increase;

  • possible flow instabilities due to the onset of slug flow;

  • pipeline integrity failure due to corrosion caused by stagnant water.

The standard procedure for pipeline liquid removal is the mechanical pigging operation, which might be, in specific cases, extremely risky or even impossible (lack of available pressure or too large liquid accumulation along the pipe). In addition, pigging is not always feasible due to the presence of trunk junctions, formation of organic and inorganic deposits or any other restriction making pigging operation unsuitable due to the risk of pig blockage. Under these conditions, the do-nothing-option seems to be the most applied one, with consequent reduction of the pipeline lifetime.

The new approach here presented is based on a batch injection of innovative foam (a blend of fit-for-purpose tension-actives plus other components), which is acting as an additional phase, displacing some or all the liquid accumulated along the pipeline just like a rigid pig, but avoiding the risks connected to the possible pig blockage (the foam, at increasing pressure, would dissolve and mix with the fluid already present in the pipeline).

To better optimize injected foam quantity and quality, a proper displacing operation simulation is required to:

  • Identify the amount and characteristics of the injected foam.

  • simulate the trend of discharged liquid to the separator in terms of surge liquid volume and evaluate the length of the procedure;

  • evaluate the reduction of the pressure drop and the possible increment in terms of gas and liquid production that can be achieved after pipeline foam operation;

  • predict the operation frequency due to liquid accumulation rate evaluated by the code;

To accomplish this task, a foam module has been implemented in MAST, with following capabilities:

  • a separate fluid phase (foam) is considered in the numerical solver, characterised by foam main parameters (density, viscosity, surface tension, quality)

  • gas/oil/water interaction with foam is simulated, to predict foam transport capabilities and foam collapse due to pressure/friction/liquid loading;

Preliminary results of the model have been retained satisfactory when compared with a field application of the foam pig in unloading a gas pipeline

Introduction

The deployment of foam agents for liquid displacements is relatively new in the oil and gas sector. Typically, a mechanical pig is used for displacing the accumulated liquid in order to increase the production. Nonetheless the present paper focuses on this novel operational procedure and in particular it will describe the envisaged foamer module which has been implemented in MAST [1], [2], a transient one-dimensional multi-phase flow simulator. For an industrial prospective, it is of paramount importance the feasibility of performing numerical simulations with tools providing accurate results, addressing solutions of the specific problems. To the authors present knowledge, no available industrial one-dimensional code permits to conduct the simulation of a foam agent added into a multi-phase flow line; this is the main motivation behind the present work. In what follows, a brief introduction to the MAST code will be given; then the foamer module will be thoroughly described and an application test case with real data will be illustrated for the sake of the code validation.

This content is only available via PDF.
You can access this article if you purchase or spend a download.