Abstract

The key theme which this paper will emphasise is minimising operating costs in wells prone to fluid losses by the development of new, innovative technology.

Fluid losses occur when the hydrostatic pressure in the well exceeds that which the reservoir can support. If the formation has a high productivity (injectivity) index, then losses can be severe. Fluid losses are highly undesirable for a number of reasons:

  1. extended well kill operations are expensive in terms of both rig time, consumable costs and deferred production;

  2. lost fluid must be back produced, further deferring production;

  3. pump life can be reduced by reverse rotation of the impellers; and often most importantly,

  4. permanent impairment of well productivity can arise through formation damage.

The tendency for fluid loss problems is increasing generally due to:

  1. the large number of mature, pressure-depleted reservoirs under artificial lift;

  2. the growing number of high productivity, long reservoir section wells being drilled.

A number of Operators stated a requirement for a device to prevent fluid losses in producing wells, with particular emphasis on compatibility with ESP completions. As well as discussing the need for fluid loss control, this paper presents the development and operational history of a fluid loss control mechanism, designed to meet the following requirements:

  1. prevents fluid loss to the reservoir when activated, both during production and workover operations;

  2. allows reservoir access when desired (for logging surveys, chemical treatments, etc.);

  3. offers long term >5 year) life expectancy;

  4. ensures easy installation and recovery in high step-out, deviated wells;

  5. can be repeatedly opened and closed;

  6. can be used with or without an ESP bypass facility;

  7. has maximised through bore, for both reservoir access and minimum restriction to flow;

The solution to these requirements draws upon pipeline valve technology to produce a remote system, featuring an unusual, normally open check valve. The paper reviews the operational performance of the current installations of this system, including specific well applications.

Background

The number of wells being produced using electrical submersible pumps (ESP's) is increasing. This is due to the growing number of fields undergoing artificial lift, combined with the improving reliability of ESP's.

Such wells often exhibit a tendency for losing fluid to the formation, especially during workover operations and when producing high water cut fluids. In these situations the hydrostatic pressure of the fluid column may exceed the reservoir pressure, giving an overbalance driving force. The severity of the fluid losses then depends upon the injectivity index of the formation. High permeability formations and long, horizontal wells are especially prone to severe fluid losses.

Implications of Fluid Loss. There are a number of major implications of fluid loss, both during workover and production operations.

Workover Operations. Fluid losses can lead to expensive workover operations, due to the costs associated with rig time and consumables. Additionally, production is deferred by ESP down-time and subsequent back-production of lost fluids. Finally, and often most importantly, kill fluid incompatibility with the formation can lead to formation damage. Repeated workover activities can lead to a permanent reduction in well productivity.

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