Abstract

Offshore well intervention with coiled tubing (CT) in the Niger Delta has traditionally been rig-based. Experience has shown this type of activity to have high cost implication both cash wise as well as in time. With the current focus on development of offshore marginal fields, it has become imperative to perform well intervention operations at a more reduced cost to the operator.

Non-rig based interventions can provide an economic advantage. However, inadequate facilities on existing offshore platforms and jackets present additional challenges. Furthermore, performing well intervention from a supply vessel is definitely not a mean task. Despite the complexity of this type of activity, the cost savings for not mobilizing a rig usually makes small intervention work that would increase oil production attractive to operators from the standpoint of ROI, vis-à-vis comparing the cost of the total intervention to the projected production gains. To the smaller operators and marginal field developers, this opens up a world of opportunities.

This paper explores these opportunities and discusses how they are being exploited to yield optimum benefit for the marginal producer. The success of carrying out various types of well intervention work on four wells (two dual completions and two single completions) is showcased as case histories.

Introduction

Drilling activities offshore Nigeria dates back over forty years, with quite a lot of offshore platforms erected in that period.

In recent times the focus has shifted to Deep water, with increased investment by major producing companies, some of them have formed new offshore divisions to handle these deep water leases. These companies have prospected; some have made large oil and gas discoveries, and are currently in the process of developing these offshore fields in the Niger delta. Due to the shift of focus of the Majors to these new large offshore fields that require obviously a lot more investment, and also due to Nigerian Government regulations that require that on the expiration of an Oil Prospecting Licence (OPL) the fields must revert back to Nigerian National Petroleum Corporation (NNPC) for another bidding round, these older fields (the ones considered less viable by the majors) have been returned to NNPC and subsequently reallocated after a bidding round to indigenous oil companies and the Government-owned subsidiaries.

These companies find themselves inheriting wells that are marginal producers with old facilities that not of modern design. Generally these offshore platforms are in water depths ranging from 30 ft to 250 ft. Most of the facilities are four legged platforms with limited deck space, while others are caissons i.e. a single circular beam piled into the sea bed sealed at the top and filled with compressed air to keep water and mud out at depth. Typical configurations for some of these platforms which have 3 decks are: a boat landing deck at 6 ft above the sea level, wellhead deck at 24 ft above sea level, and the helicopter deck at 60 ft etc (Fig. 1).

The common challenges for intervention in such installations include:

  • Inadequate deck space.

  • Inadequate crane capacity - In the reviewed case histories the platforms involved did not have cranes.

The producing wells are draining mature reservoirs. Combined with the difficutly of access, they are can be candidates for an extensive amount of intervention work such as matrix acidizing, water control, scale removal, and sand consolidation to maintain an economic production rate.

Due to the scarcity and high cost of jack up rigs to carry out the various remedial interventions, there are obvious advantages of utilizing barge mounted CT as the means of providing solutions.

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