Abstract

With today's oil and gas prices, the loss of well production creates a negative financial impact on operating companies, especially in an offshore environment.

One of the most common reasons for production loss is the development of scales inside the production strings, blocking the flow of the reservoir fluid to the surface facilities. Barium Sulfate (BaSO4) scale is among the toughest scales to remove, whether mechanically or chemically. Alternatives to remediate this problem are often quite costly.

Therefore, under this scenario, a cost-effective intervention mechanism to restore production to previous levels is imperative. One of these mechanisms is the deployment of coiled tubing intervention as it can be done while the well is still live, minimizing further loss of production.

The Namorado field in Campos Basin, offshore Brazil, has approximately 60 wells, with most of them presenting deposition of BaSO4 scale throughout their production history. Historically, in this field, the deployment of a down hole motor with coiled tubing has been effective, but limited to restoring the production path's diameter only to the outer diameter of the bit. Results with deploying a down hole motor have been satisfactory. On the other hand, chemical treatments have been extremely ineffective and are, therefore, seldom deployed.

This paper presents two case histories of successful Barium Sulfate scale removal from the production tubing by coiled tubing, utilizing a combination of mechanical and hydraulic tools. This process is different from the conventional method (downhole motor) as it provides faster cleanout rates and quicker production restoration. This combination is engineered through software that optimizes the velocity at which the coiled tubing string is run through the scale, as well as the configuration of the hydraulic tool with respect to the pump rate and selection of the jet angle.

Introduction

One of the most common reasons for production decay in oil and gas wells is scale formation inside the production tubing. In Namorado Field, Campos Basin, Brazil, the management of Barium Sulfate (BaSO4) scales is one of the most challenging objectives for the production maintenance at the field.

The Namorado Field suffers, as many oilfields do, from serious scale deposition issues. In particular, the field faces a plague of hard, stubborn Barium Sulfate scale (Figure 1).

Despite periodic scale inhibition treatments, many wells still suffer flow restrictions as scale deposits diminish the internal diameter of production tubing. A typical solution has been to remove and replace the production tubing, an expensive proposition because of environmental regulations treating barium sulfate-contaminated tubing as radioactive waste.

Since the advent of water injection at the Namorado field, by the middle of the 1980s, laboratory tests indicated the high potential of Barium and Strontium Sulfate precipitation to occur at wells using this technique.

During this time, several procedures were analyzed and implemented in order to prevent the occurrence of BaSO4 scale formation and to remove scales already in the tubing as well.

In general, scales can have different sources and compositions and can be formed by different factors, such as:

  • Increase or decrease in temperature

  • Increase or decrease in pressure

  • Increase or decrease in salinity

  • Increase or decrease in pH

  • Mixing of two or more different waters

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