Abstract

HSE training, implementation & production results for a long term underbalanced coil tubing multi-lateral drilling project.

The methods used to safely implement the bp Sajaa CT UBD project from start up issues through implementation will be discussed. To date, 14 wells have been drilled successfully with no accidents, the decline in the gas production for the Sajaa field has been mitigated and additional reserves have been accessed. This has been achieved through a programme of training, teamwork and service company integration leading to new heights of HSE performance for the industry. In addition, the key learning's have been carried forward from well to well to optimise the economics of the project and open up new opportunities previously thought to be unfeasible. Through a series of innovative engineering applications, the future of the project has been secured.

Introduction

Located in the Emirate of Sharjah, United Arab Emirates, the Sajaa onshore gas field is a Thamama limestone reservoir ranging from 11,000 to 13,000 feet true vertical depth. The bottom hole temperature is in the range 260 to 310 degrees Fahrenheit with bottom hole pressures of 1,100 to 1,900 psia. This paper will discuss the HSE (Health Safety & Environmental) training that took place in preparation for implementation including both bp corporate initiatives and more site and job specific training, and the way this was carried forward to the wellsite to aid a successful start-up. In addition the practical implementation will be discussed including ‘maintenance’ of the training programme and finally go on to present the results achieved to date in both HSE and well achievements.

Background

In April of 2002 a Production Technical Limit (PTL) meeting reviewed the wells and reservoir in the Sajaa field and identified the prize of unlocking additional permeability and height to gain additional rate and reserves. The PTL also identified the work required for sub surface evaluation of the reservoir with the basic questions of how much gas is left and where the gas is located. Ideas were then put forward on various options of snub drilling, conventional underbalanced drilling as in the 2000 campaign, and coiled tubing drilling. All the options had one thing in common and that was the use of multi lateral wellbores to connect gas zones not fully connected with the vertical well mother bores. Coiled tubing drilling was evaluated as the best choice because of the need for real time directional steering where mud pulse is not possible due to the two phase fluids being pumped down the coil.

In June of 2002 a peer assist was held in Sharjah with invited bp guests as well as distinguished underbalanced, CTD & snubbing experts from other bp locations worldwide, service companies and underbalanced consulting firms. The result of the three-day meeting was a risk assessment of Underbalanced Coiled Tubing Drilling in the Sajaa field. Key areas of risk were identified as:

  • Personnel (right people, right skill sets, doing the right thing)

  • High temperature equipment (300 degrees F assurance testing)

  • Staffing levels (supervisory and operators)

  • Two phase milling of nipples and windows

  • Equipment availability

  • Nitrogen (liquid versus membrane)

  • Coil purchase, owner and lead-time

  • Formation deliverability

  • Loss of mother bore

A basis of design (reference 1) allowed bp to model various possibilities before a contracting tender strategy was prepared. This strategy leaned heavily on a pre-qualification of companies to screen those with acceptable HSE and Management Systems prior to the technical and financial bidding process. A high emphasis was placed on front end loading for the project and significant time was spent in planning and engineering work before any equipment was mobilised to the wellsite.

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