During the past five years, it has been well documented that drilling in underbalanced wellbore conditions can increase well productivity. This finding has led to a resurgence of interest in applying this concept. In wells where relatively high rates of produced hydrocarbon are anticipated, however, the traditional drilling flow-back systems have not always been successful in providing the safety, operational efficiency, and data management capabilities needed.

This paper focuses on a new, built-for-purpose, underbalanced drilling, 4-phase, surface-separation and well-control system that couples the mechanical flow requirements of the underbalanced drilling environment with the safety and efficiency of a process facilities design.

The discussion will focus on the design intent, prototype testing, commissioning and first operations of the system.

The system incorporates:

  1. Progressive separation and solids-handling techniques to improve separation efficiency.

  2. Programmable Logic Controller (PLC) technology to improve operational safety in the event of emergency or process upset conditions.

  3. Strict adherence to codes and industry practices, ASME B&PV (pressure vessels), ASME B31.3 (piping systems), API RP 14C (surface safety systems), NACE MR0175 (H2S service metallurgy), API RP 500 (Electrical Installations), etc.

  4. State-of-the-art real time data acquisition, data transmission and reservoir modelling techniques to better control the drilling process.

The system can safely and efficiently control and measure all returns, both drilling and production, while wells are being drilled by underbalanced means.

The system was designed and built in 1999 and underwent pre-commissioning and testing in December of that year. Pre-job commissioning was carried out in two locations during the first and second quarters of 2000.

The system provides a fully integrated underbalanced surface system capable of meeting the requirements of today's prolific underbalanced drilling candidates. Since commissioning, the system has been used on several underbalanced wells, and the results of the first deployments demonstrate that underbalanced drilling programs exhibiting high rates of produced hydrocarbon on surface can be undertaken without compromising operational safety, flexibility and integrity. Elements of data such as reservoir pressure; flow rates; gas composition; and mechanical drilling data can be incorporated into a single job database that can facilitate on-site data access, data manipulation, data transmissibility and analytical capability. Thus, timely and more effective on-site decision making results.

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