Abstract

A major phenomenon altering well productivity is increasing water production. In addition to raising energy consumption, higher water production leads to phenomena such as mineral and organic scaling, which may temporarily or even permanently alter the whole flow assurance chain. The build-up of scale inside well bore can smother a productive well within 24 hours, causing millions of dollars in damage every year.

A project was carried out to review and to evaluate new techniques and tools developed for scale treatments in order to find an appropriate tool, at least deployed with wireline rather than with coiled tubing (CT) to overcome the adverse scale problems encountered in most of the fields. This paper presents results of this evaluation and shows the advantages and disadvantages of different tools for scale removal process. Solid blasters, deployed with CT, have proved to be efficient in removing most of the scales but it is costly as well as inapplicable to wellbore and near-wellbore. Tools using fluidic oscillator technology is not that expensive, however they are not strong enough to treat very hard scales like barium sulphate. In addition, these tools have great standoff distances and are deployed with CT. String shots, wireline-deployed, are good for short intervals, thin layers of scales. Recent techniques, which use acoustic waves to clean the near wellbore damage are not good tools to be applied for tubing and casing scale depositions since they have only proved to have the ability to remove fines and soft materials like mud cakes from near wellbore region.

Introduction

Declining oil production is of major concern in the oil industry. This decrease is often due to scale deposition. Unfortunately, this is an issue becoming more and more important as the oil reservoirs are depleted and the number of EOR projects including water and gas injection goes high. As the oil reserves decreases, the conditions of production get more severe, favoring the formation of scale. Scale is defined as the secondary deposit of mainly inorganic chemical compounds caused by the presence or flow of fluids in a system at least partially man-made1. In other words, it is an assemblage of deposits that cake perforations, casing, production tubing, valves, pumps and downhole completion equipment, thereby clogging the wellbore and preventing fluid flow. Scale can be deposited all along water paths from injectors through the reservoir to surface equipment. Most scale found in oil fields forms either by direct precipitation from the water that occurs naturally in reservoir rocks, or as a result of produced water becoming oversaturated with scale components when two incompatible waters meet downhole. For situations of injected sea water breakthrough the problem is especially great as the growth is often barium, or strontium sulphate, both of which are almost completely insoluble. The direct cost of removing scale from one well can be very high, and the cost of deferred production even higher.

Although many tools using different cleaning technologies have been developed, none of them has proved to be the perfect solution to be applied in any severe cases. Actually each tool has its own pros and cons thus having limited range of applicability.

Before recent developments in scale-removal technology, operators with hard scale problems in their production tubing were often forced to shut down production, move in workover rigs to pull the damaged tubing out of the well, and either treat for scale at the surface or replace the tubing. One of the earliest scale-removal methods was an outgrowth of the use of explosives to rattle pipe and break off brittle scale. Explosives provided high-energy impact loads that could remove scale, but often damaged tubular and cement[2].

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