Introduction

The Sajaa Gas field, producing from the Thamama carbonate formation, is a prolific and important gas producing field for BP-Sharjah and its partners in Sharjah, United Arab Emirates.1

In December 2002, BP-Sharjah decided to embark on a through tubing coiled tubing UBD campaign to drill underbalanced, horizontal multilateral sidetracks to increase wellbore deliverability in this low pressure environment.2

Due to the probability of cross-flow between multilateral legs due to variations in reservoir pressure and the existence of high intensity fractures, maintaining dynamic pressure control presented a significant technical challenge. Safely detecting and responding to rapid changes in a complex well geometry with a very small volume well annulus was of paramount importance. Adequate crew training and effective communication between rigsite decision-makers was considered to be essential success pre-requisites for conducting safe operations.

An intense two day training program using an advanced dynamic well control computer simulation was developed to prepare key rigsite personnel prior to operational startup. Eleven problem exercises were simulated during this team based training exercise.

The goals of the training program were to:

  1. Initiate team building between personnel supplied by various service companies who had not previously worked together

  2. Increase awareness of expected well control dynamics when drilling multilaterals and penetrating fractures

  3. Heighten crew alertness to potential problems and appropriate mitigation response

  4. Assess technical competency and compatibility between team members

The purpose of this paper is to discuss the unique features of the training program format, well problem scenarios, and simulation exercise results so that key lessons can be applied to improve the safety of future projects containing similar operational challenges.

Well Geometry

Coil tubing drilling operations were planned to occur inside the previously run well completions. Figure 1 depicts the well geometry for the first well, Sajaa #3. The primary completion consisted of 5" tubing hanging freely inside of 7" casing. Coiled tubing geometry consisted of 2–3/8" coil, 3.00" BHA and 4.10" bit.

It was planned to run a through-tubing inflatable whipstock above the existing perforations, cut a window, and then sidetrack drill three, 3500' horizontal multilateral sections oriented in a "crow's foot" configuration. Reservoir pressure was anticipated to be 1300 PSI at the top of the reservoir (11,000 ft TVD).

Simulator Description

Material for the training course was developed using a PC based advanced software simulation product called UbitTS - Under-Balanced Interactive Transient Training Simulator. UbitTS combines an industry proven mechanistic two phase transient hydraulics flow model (OLGA) with a highly interactive and graphical user interface. This combination enables users to learn by trial-error methods to improve their understanding of the cause-effect relationship of varying injection rates and return surface pressures.

Figure 2 shows an annotated view of the main simulator interface and graphical user controls for:

  1. Gas injection rates

  2. Liquid injection rates

  3. Return choke opening

  4. Separator setpoint pressure

  5. Surface tank management actions (add, transfer, and dump liquid volume)

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