Abstract

Non Productive Time (NPT) in cementing operations is attributed to one or more of the following causes;

  1. Hole conditions,

  2. Cementing operations,

  3. Surface equipment failure,

  4. Casing equipment failure.

The necessity to obtain good zonal isolation between limestone reservoirs has led offshore operating companies in Abu Dhabi to use mechanical devices over the previous years to achieve these objectives but with mixed results.

Over recent years, the introduction of multilateral technology and challenging well profiles have led to an increase of non-productive time in cementing operations mainly due to casing equipment failures. In 1996, a multidiscipline team was formed to review failure case histories and to draw up an action plan for reducing Non Productive Time (NPT) in cementing operations.

This paper describes a solution to a high Non Productive Time (NPT) in cementing operations where 45% of the failures were attributed to External Casing Packers (ECP) and Dual Valve Packers (DV).

The team recommendations were to eliminate DV packers in 9–5/8 inch casing strings and to adopt single stage cementing techniques. A parametric study was conducted using a cement simulator in static and dynamic conditions to assess the associated risks (losses, Fractures) whilst cementing 9-5/8 inch casing strings set at 9,000 ft with 4,000 ft of open hole, using single stage cementing techniques.

In late 1996, five successful single stage cementing trials were carried out on oil producers and water injectors. The main objectives to obtain zonal isolation between reservoirs and to bring cement to the surface or close to surface were achieved. NPT in cementing operations was reduced drastically and a plan to generalize single stage cementing techniques for all well types with the use of special cement slurry designs is being studied. Detailed statistics of the failure ratio before and after implementation of these methods are given and guidelines to successful job execution by a "team work" approach are provided.

Introduction

ADMA OPCO operates offshore fields situated in offshore Arabian Gulf between 80 km and 120 km North west of Abu Dhabi island hence drilling activities for others OPCO's whose leases are located offshore. Nearly one thousand wells have been drilled so far on these concessions whereas oil was first discovered in late fifties early sixties. Production is expected to be sustained at plateau rate for the next 25 years and to be extended beyond year 2050 with the introduction of new enhanced recovery techniques. The majority of the produced oil is coming from stacked reservoirs of Cretaceous limestones called in the area Thamama and Arab groups. Reservoir pressure is maintained by a water injection program (in fill and boundaries) which sustains pressure and enhance recovery.

A typical well design for offshore fields in Abu Dhabi, is to set the 9–5/8 inch casing at 9,000 feet (M.D.) in the dense zone of the Thamama reservoir, with a DV packer tool located 150 feet inside the 13–3/8 inch casing at approximately 5,000 feet as illustrated in the well schematic (Fig. 1). The cementation is then carried out in two stages with the aim to bring cement of the second stage, back to surface.

In 1996 a series of 9–5/8 inch casing DV packer tool failures led to the formation of a multidiscipline task force whose mandate was to review the extent of the problem, analyze different solutions and propose remedies to reduce Non Productive Time of cementing operations due to down hole equipment failures.

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