Concept Select and Preliminary Front End Engineering and Design (Pre-FEED) were carried out on a long-term development plan (LTDP) for a brown oil field with nearly 200 existing Wellhead Towers (WHTs) and four existing artificial islands in the middle east area. The development objective is ramping up the production to certain rate and sustain it as long as economically feasible.

This paper will describe:

  1. Critical stuff that needs to be performed or taken into account from drilling perspective during Concept Select/Design and Pre-FEED

  2. How the drilling discipline should be proactively engaged through Concept Select and Pre-FEED for development project of offshore brown oil field

During the Concept Select, necessary data related to drilling was firstly collected such as well target locations, available slots on existing WHTs etc. In addition to that, several assumptions were set, associated with drilling rig specifications, constraints on drilling feasibility and number of well slots on new WHT. Based on the data and assumptions, multiple concepts were developed with respect to different drill centers including new WHTs, new artificial islands and existing WHTs/islands in coordination with other disciplines. Techno-economical evaluation was conducted on each concept.

Subsequently, Pre-FEED was conducted based on the selected concept. During the Pre-FEED, more detailed study on WHT locations, WHT orientations, WHT design, island location, island design, HSE assessment etc. was conducted by Pre-FEED contractor, incorporating basis and requirements from all the concerned disciplines.

Through the Concept Select and Pre-FEED for Long Term Development Plan (LTDP), following things were found important:

  • Generic drilling limits like maximum horizontal departure to targets should be defined clearly at early timing of Concept Select for optimization of well allocation to drill centers

  • Rig specifications and its limits like air gap, skidding envelope and allowable drilling load should be identified at early stage for optimization of WHT design/locations and island design

  • Slot-to-slot distance and row-to-row distance are quite important especially for island in terms of rig operability on island and anti-collision between wells

  • Requirements for area and its arrangement on island should be well defined item-by-item to avoid shortage in the area dedicated for drilling during subsequent stage of project

  • Anything that needs to be studied or considered by Front End Engineering and Design (FEED) contractor should be captured in FEED Scope of Work (SoW) with detailed requirements, which will be utilized for tender process. Anything that is not captured in the FEED SoW could result in variation order or be difficult to be added to the scope after contract award.

This paper will present not only the experience in this specific project but also a fundamental approach that will be applicable in any other offshore brown oil fields worldwide.

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