ABSTRACT

Two phase air/water and three phase air/oil/water experimental runs were performed on 0.0259m internal diameter pipe to investigate wrne patterns and characteristics of pressure toss and hold-up for each system. [n combination with a database of results a flow regime map was formulated independent of pipe diameter and taking into account fluid properties detailing the spectrum of two add three phase wave patterns and classifications. The latter being tested for gas/oil flows and diameters rangingfiom 1"to 3.5".

The subject areas of pressure Ioss and hold-up, in two and three phase flows are also investigated with semi empirical relationships being made for two phase air/water flows using the momentum balance between the respective phases to predict interracial shear stress. The range of separated ppe flows was attained with reasonable success however difficulties are encountered with intermittent flows. Suggestedmodifications to the momentum balance for the prediction of three phase pressure gradient and phase slippage are alsooutlined.

The prospect of predicting multiphase flow characteristics may enable direct onshore conveying with minimum separation facilities or to a central processing platform. .4s a consequence, this will sense to stimulate enhanced oil recoveryin high water cut reserves and promote the operation of marginal fields at optimum processing conditions.

INTRODUCTION

The prospect of diminishing reserves and greater environmental awareness within the industry in contrast to the previous large-scale developments of the 70's and 80's, now in decline, has focused attention on the advancement of near, high GOR, offshore and ageing gas fields. Set against this background, together with rising platform costs and safety considerations, the concept of conveying the full well stream, after primary separation, to a main processing platform or directly onshore, is being continuously reviewed. If the transportation characteristics of such mixture can be determined then an opportunity exists to exploit such marginal fields more economically, However the dictating factor of the oil price will again play a major role in any future ventures. Generation of three phase mixtures may originate from any one of the following.

  • Mature Provinces - High water-cut

  • Artificial production techniques

  • Enhanced oil recovery methods

Successful field development, reservoir management and optimum operational control requires detailed knowledge of the flow characteristics for both two and three phase flow networks to include pressure loss and hold-up parameters and their variation with oil-in-water percentage.

The addition of another phase presents as many obstacles as solutions. Some of the problems with the installation of a three phase pipeline network are detailed below :

  • Oil/Water theology (Phase Inversion)

  • Hydrate formation

  • Mass transfer between phases

  • Emulsification / Post separation

  • Significant head requirements

  • Excessive oil/water corrosion

  • Water disposal (40 ppm)

Thus to fully appreciate two phase / multiphase flow in the context of exploiting marginal fields, it is necessary to commence from a base with which comparisons may bedrawn.

While two phase flow strings have been adequately covered by various workers a degree of variation exists for thecategorisation of wave patterns

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