Full Scale Kick Experiments in Horizontal Wells
Authors: Rommetveit R. , Bjorkevoll K.S. , Bach G.F. , Aas B. , Hy-Billiot J. , Maglione R. , Gie P. 
Published: December 2007

Full scale gas kick experiments have been performed. The objectives of the experiments were to gain more knowledge during the circulation out of gas kicks in a horizontal well through the study of the behaviour of the two-phase flow at high pressures.

The horizontal wellbore was simulated on the surface by a 200 m long flow loop (casing) with an inside diameter of 9 1/4". The inside of the well had a drillstring with a 50 m long drill collar section. The drillstring assembly could be rotated. Also, the last 50 m of the well near the bit was inclined upward with 4 from horizontal for part of the experiments. The wellbore was designed for pressures up to 170 bars.

The gas used during tests was air. Two different liquids; water and CMC polymer solution, were tested. During the experiments the main parameters varied were mud circulation rates, gas injection rates, system pressure and drillstring rotation.

Three test categories were performed. During DISPERSION tests, single bubbles of gas were injected and circulated out in order to study the gas dispersion along the horizontal well.

During FLOW TESTS, a continuos injection of gas was performed to study gas velocity, flow regime and pressure loss.

During CLEAN-OUT TESTS, methods for circulating out stationary gas positioned in traps in the well were studied.

New correlations for gas transport velocities and frictional pressure losses have been developed based on these data as well as data from two low pressure flow loop tests.

Results from the full scale tests as well as the new correlations are presented in this paper.

Introduction

Gas kicks may develop into major well control incidents. A gas kick situation in a horizontal well may for the future occur more frequently than today. The industry is moving towards fewer appraisal wells and early production. This may lead to pressure surprises. Also horizontal well drilling in reservoirs with water or gas injection or in depleted reservoirs may lead to surprises related to pressure.

Studies related to kick development and control have been performed. These include full scale experiments, development of kick simulators and the related gas rise velocity models. Studies on kick control in horizontal wells have been few. These include computer simulations, well control evaluations and experimental studies. The results from the experimental studies have been implemented into a horizontal kick simulator. These experiments were performed at low pressures. and in a 12 m long model loop.

It is important to study gas kick development and control in horizontal wells, for two reasons mainly. First, development of general procedures and guidelines for well control of horizontal wells are needed, procedures like minimum mud velocities for gas clean out in a given mud/well; or procedures to clean out gas when minimum clean out velocity is unobtainable etc.

Secondly, further development of models related to gas kick development and control in horizontal wells are needed. Such models will be important parts of and inputs to the development of advanced kick simulators for horizontal wells. Horizontal wells vary tremendously related to angle, build-up, length, detailed profile and existence of gas traps in the well. In order to develop well specific well control plans and procedures. simulations with an advanced kick simulator for horizontal wells is necessary.

The most important models are those for gas transport velocities, frictional pressure losses and removal rate by gas dissolution. Gas transport velocities are significantly higher for annuli than for pipe flow.

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